Stereoselective Olefination with Sterically Demanding Julia-Kocienski Reagents: Total Synthesis of Oxo-prothracarcin, Oxo-tomaymycin, and Boseongazepine B.

Total syntheses of three pyrrolo[1,4]benzodiazepine anticancer antibiotic family members oxo-prothracarcin, oxo-tomaymycin, and boseongazepine B are described. The total syntheses feature late-stage stereoselective olefination employing modified Julia-Kocienski reagents that can be conveniently prepared in only two steps and allows for a significant reduction in the number of linear steps. Detailed density functional theory (DFT) studies explain the stereochemical outcome of the key step.

Introduction

Pyrrolo[1,4]benzodiazepines (PBD) are a class of naturally occurring anticancer antibiotics.[1,2] A characteristic structural feature of PBDs is the right-hand twisted three-ring system possessing electrophilic imine functionality at N10-C11 (Figure ) known to bind covalently to the minor groove of DNA via an exocyclic amino group of the guanine base.[3−5] As a consequence, interference with DNA repair, replication, transcription, and thus cell division is observed. Also, the N10-C11 amide group-possessing PBDs exhibit considerable cytotoxicity in various cancer cell lines acting as noncovalent binders.[6] A number of naturally occurring and synthetic PBDs have been studied in clinical trials, and nowadays, the PBDs are considered a privileged warhead scaffold in the development of antibody–drug conjugates (ADCs).[7−9] Structurally, several naturally occurring PBDs possess an exocyclic alkylidene group at the C2 position. Studies in synthetic PBD series also reveal that this alkylidene substituent is crucial for the superior cytotoxicity of these compounds.[10]

Figure 1

Representative examples of the C2 ethylidene group-possessing PBD natural products.

Results and Discussion

Recently, a scalable route toward ethylidene group-containing oxo-tomaymycin has been reported by Sanofi, revealing an important role of alkylidene PBDs in the ADC development process.[11] Although several total syntheses of alkylidene PBDs have been reported, a stereoselective introduction of the C2 exocyclic double bond remains a considerable challenge. For example, direct carbonyl olefination methods (Wittig and Julia–Kocienski) on PBDs or closely related proline scaffolds mainly give the undesired Z-isomer predominantly or lack E/Z selectivity at all.[11−15] As an alternative, strategies based on Ireland–Claisen rearrangement[16−18] or asymmetric enolate α-alkylation[19] for the stereoselective introduction of an alkylidene substituent have been developed. However, the desired 3-ethylideneproline building block is typically obtained in a 9–12 step linear sequence and a low overall yield. In 2018, our group reported a formal total synthesis of limazepine E (3) based on late-stage Julia–Kocienski olefination with sterically demanding phenyltetrazole sulfones.[20] Herein, we report a further extension of this methodology, resulting in the total synthesis of oxo-prothracarcin (4), oxo-tomaymycin (5), and boseongazepine B (6).

Our retrosynthetic analysis (Scheme ) was based on late-stage Julia–Kocienski olefination of trione 8. The tricyclic PBD scaffold can in turn be constructed from readily available anthranilic acids and trans-4-hydroxy-l-proline ester (H-Hyp-OMe) via a one-pot coupling-cyclization sequence[21] followed by oxidation of the C2 hydroxy group.

Scheme 1

Retrosynthetic Analysis of Ethylidene PBD Natural Products

We started our synthetic studies on simple A-ring unsubstituted PBD trione 10a and studied the key Julia–Kocienski olefination step (Table ). During our previous studies on olefination in the PBD series, the phenyltetrazole-based sulfones turned out to give the best results in terms of E/Z selectivity and yield;[14,20] therefore, further studies in this direction were conducted. After the initial assessment of reaction conditions (see the Supporting Information, Table S1), a series of new and known phenyltetrazole sulfones were examined in Julia–Kocienski olefination of A-ring unsubstituted PBD trione 10a (Table ).

Table 1

Phenyltetrazole-Based Julia–Kocienski Reagent Screening for the Olefination of Trione 10abc

0.150 mmol 10, 0.450 mmol 11, 0.450 mmol KHMDS, tetrahydrofuran (THF) (4.2 mL), −78 °C to room temperature (rt).

Determined by QNMR; brsm, based on recovered starting material.

Determined by high-performance liquid chromatography (HPLC).

First, the electronic effects of substituents in the phenyl ring of phenyltetrazole sulfones 11 were studied (Table , entries 1–5). In general, good selectivity (up to 88:12) toward the desired E double-bond isomer of 12a was observed in all cases. The electron-donating methoxy group in the phenyl ring (entry 2) gave a comparable E/Z ratio compared to simple phenyl (entry 1) but a slightly lower yield (72 vs 86%). In contrast, the electron-withdrawing cyano group (entry 3) completely shut down reactivity and most of trione 10a was recovered. Similarly, for 2,5-dimethoxy substitution (entry 5), the formation of 12a was not observed. Interestingly, the electron-withdrawing fluorine substituent in the phenyl ring (entry 4) gave an even higher E/Z ratio compared to simple phenyl (entry 1) but a slightly lower yield (66 vs 86%). Next, the steric effects of substituents in the phenyl ring of phenyltetrazole sulfones 11 were studied. As known from our previous studies,[20] the introduction of ortho-substituents in the phenyl ring of the Julia–Kocienski reagent increases the E/Z selectivity of the olefination. The introduction of two ortho-methyl groups (entry 6) only slightly increased the olefination stereoselectivity; however, sterically demanding isopropyl (entry 7) or cyclohexyl (entry 8) groups allowed for an increase in the E/Z ratio up to 88:12 compared to 72:28 measured in the case of the classical Julia–Kocienski reagent 11a (entry 1). Due to the concise synthesis (vide infra), the comparably high E/Z selectivity and higher olefination yield of 2,6-di-isopropylphenyl-substituted phenyltetrazole sulfone 11g (entry 7) was selected for further studies. With the optimal sulfone substitution pattern in hand, olefination solvent screening was performed; however, the initially used THF turned out to be superior to others (see the Supporting Information, Table S2). The next task was to develop a high-yielding and scalable preparation procedure for the synthesis of sulfone 11g (Scheme ).

Scheme 2

Optimized Synthesis of Sulfone 11g

In analogy with the literature known procedures,[22] sulfone 11g was successfully synthesized in decagram quantities starting from readily available thiocyanate 13g (Scheme ). The developed method allowed obtaining sulfone 11g in 90% yield over two steps with only one isolated intermediate 14g. It is important to note that sulfone 11g was successfully prepared without any chromatographic purification and the final crystallization gave 11g in 99% purity (according to HPLC).

After finding the optimal Julia–Kocienski reagent structure and optimized reaction conditions, we turned our attention toward the scope of our developed methodology in the PBD series (Scheme ).

Scheme 3

Substrate Scope of the Julia–Kocienski Olefination of Triones 10

Olefination of triones 10 typically proceeds with good E-selectivity in all cases, and the E/Z ratio can be significantly improved by our optimized Julia–Kocienski reagent 11g (Scheme ). Employing sulfone 11g, the reaction yields are moderate, ranging from 48 to 70%, which is caused mostly by partial deprotonation of α protons of the keto group of 10, resulting in a ketone enolate not being able to participate in the olefination reaction. This hypothesis was confirmed by quenching of the crude reaction mixture with D2O, which resulted in partial deuteration of unreacted substrate 10. Additives like CeCl3[23] or LaCl3*2LiCl,[24] known to suppress α-deprotonation of carbonyl compounds with organometallic reagents, unfortunately, did not increase the reaction yield. Fortunately, unreacted trione 10 in all cases could be easily recovered during the chromatographic purification step. Besides the chloro-, trifluoromethyl-, and dimethoxy-substituted PBDs 12b, 12c, and 12e, four natural product precursors 12a, 12d, 12f, and 12g(20) were successfully prepared by employing our developed methodology with E/Z selectivity up to 94:6. Intermediates 12a, 12d, and 12f were further converted into the corresponding natural products by a simple protecting group cleavage (Scheme ), and 12g is a common intermediate from the total synthesis of limazepine E (3).[17]

Scheme 4

Total Synthesis of Oxo-prothracarcin (4), Oxo-tomaymycin (5), and Boseongazepine B (6)

The trimethylsilylethoxymethyl (SEM)-protecting group of intermediates 12a and 12d were successfully cleaved using aqueous HCl in the THF mixture at elevated temperatures, furnishing oxo-prothracarcin (4) and boseongazepine B (6) in 55 and 62% yields, respectively. In the case of 12f, both SEM- and Bn-protecting groups were cleaved simultaneously in one step using methanesulfonic acid and anisole.[11] The spectroscopic data of the synthetic samples of all three natural products were in good agreement with the literature. The developed methodology also allows for a significant decrease in the number of linear steps (LLS) of the total syntheses of PBD natural products. For example, oxo-prothracarcin (4) and boseongazepine B (6) were obtained in seven steps compared to ten steps reported earlier.[17,21]

Although a remarkably high E/Z ratio of the olefination in the PBD series was observed, the origin of this selectivity remained unclear since the steric discrimination between both sides of the keto group in 1 was not obvious. To understand the observed selectivity, density functional theory (DFT) calculations were performed using the b3lyp/6-311++g(df,p)//b3lyp/6-31+g(d) method. To simplify the computational model, two approximations were made: (a) N-phenyltetrazole sulfone was used instead of N-(2,6-di-isopropylphenyl) sulfone and (b) N-Me substituted ketone 10 was used instead of N-SEM ketone 10 (Scheme ; for computational details, see the Supporting Information). Three distinct transformations of the olefination pathway were elaborated by the calculations: first, nucleophilic addition of the carbanion (TS-1) to the ketone to give an alkoxide; the second is the Smiles rearrangement (TS-2) during which the tetrazole subunit is transferred from the sulfinate to the alkoxide; and third, the formation of the olefine via elimination of sulfur dioxide and the tetrazololate leaving group (TS-3). The proposed pathway is in agreement with a previous study by Legnani and Vidari.[25] According to the calculations, the rate-limiting and selectivity-determining step is the first step—the nucleophilic addition of the carbanion to the ketone (TS-1). The Gibbs free energy difference between TS-1 and TS-1 was determined to be 0.8 kcal/mol in favor of the E pathway. This is in good agreement with experimental observations that the formation of (E)-olefin is favored over (Z)-olefin. The energy difference between TS-1 geometries for both E and Z pathways can be explained by a slight change in the orientation of the approaching carbanion species (Figure ). The distance from the C atom of the ketone carbonyl group to the S atom (SO2 subunit) and the C atom (methyl group) of the carbanion in TS-1 is equidistant (3.4 and 3.3 Å, respectively), whereas in TS-1, the carbanion is slightly skewed—the corresponding distances between the C atom of the ketone carbonyl group to the S atom (SO2 subunit) and the C atom (methyl group) are 3.5 and 3.1 Å, respectively. The change in carbanion orientation increases steric interactions between the Me group of the carbanion and the CH2 group of the ketone in TS-1 compared to that in TS-1. The origin of the orientation change can be attributed to the repulsive interactions of the dipoles of the SO2 subunit of the approaching carbanion and the benzylic amide subunit of the ketone. Indeed, the overall dipole moment of the TS-1 (13.4 Debye) is 11% lower than that of the less favored TS-1 (15.1 Debye).

Scheme 5

Potential Energy Surface of the Julia–Kocienski Olefination of PBDs

Figure 2

Overlay of transition-state geometries (for a detailed view, see the Supporting Information); (A) overlay of TS-1 (green) and TS-1 (cyan), (B) geometry of TS-1, and (C) geometry of TS-1.

In summary, we have developed a stereoselective Julia–Kocienski olefination approach for the late-stage introduction of an ethylidene substituent in the PBD series. The utility of our developed method is showcased in concise total syntheses of three PBD natural products, namely, oxo-prothracarcin (4), oxo-tomaymycin (5), and boseongazepine B (6). The modified Julia–Kocienski reagent can be conveniently prepared in a two-step sequence starting from commercial isothiocyanate in a column-free fashion.

Experimental Section

General Experimental Details

Commercially available reagents and starting materials were used as received. Sulfones 11a and 11h and trione 10g were prepared according to the literature.[20] All reactions in anhydrous solvents were performed under an atmosphere of argon. THF was dried over Na and benzophenone and distilled prior to use, and other solvents were purchased from commercial sources labeled as anhydrous over molecular sieves. For analytical thin-layer chromatography, Merck TLC Silica gel 60 F254 plates were used. Flash chromatography was carried out using Zeochem silica gel ZEOprep 60 (40–63 μm) for the direct phase and Biotage KP-C18-HS for the reverse phase. NMR spectra were recorded on Varian Mercury (600 and 400 MHz) and Bruker (300 MHz) spectrometers. Chemical shift values were referenced against residual protons in the deuterated solvents. Cross-peak multiplicity was marked as (s = singlet, d = doublet, t = triplet, q = quartet, p = quintet, h = sextet, hept = heptet, m = multiplet, br = broad). Infrared spectra were recorded in the range of 4000–500 cm–1 as a film. HRMS spectra were obtained on a Micromass AutoSpec Ultima Magnetic sector mass spectrometer (TOF). Optical rotations were measured on a Rudolph Research Analytical Autopol VI polarimeter. Melting points were determined using a Stanford Research System MPA100 apparatus and are uncorrected. Chromatographic analyses for determination of E/Z isomers were performed on Apollo C18-12 5 μm (4.6 × 150 mm, isocratic 70% ACN/10% (0.1% H3PO4), 1 mL/min flow rate at 40 °C) or ZirChrom CARB 5 μm (4.6 × 150 mm, isocratic 90% ACN/10% (0.1% H3PO4), 1.2 mL/min flow rate at 40 °C) columns. Crystallographic data have been registered in the Cambridge Crystallographic Data Centre and assigned the following deposition numbers for the sulfone (2152438) and PBD (2155056).

General Procedure for the Preparation of PBD Triones 10—Step 1

To a stirred solution of the corresponding anthranilic acid (110.1 mmol, 2.0 equiv) and PyBOP (57.3 g, 110.0 mmol, 2.0 equiv) in anhydrous dimethylformamide (DMF) (50 mL) was added triethylamine (TEA) (77.0 mL, 550.6 mmol, 10.0 equiv) at room temperature, and the resulting mixture was stirred for 15 min. Then, methyl (2S,4R)-4-hydroxypyrrolidine-2-carboxylate hydrochloride (10.0 g, 55.0 mmol, 1.0 equiv) was added and stirring was continued for 16 h. After that, the suspension was filtered, and the filtrate was concentrated to ∼1/2 of its original volume and subjected to reverse-phase flash column chromatography (full gradient; water/MeCN 100:0 → 0:100). The product-containing fractions were combined and evaporated in vacuo to give the title compound SI-1.

(2R,11aS)-2-Hydroxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-1a)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 1 started with anthranilic acid (15.10 g, 110.122 mmol, 2 equiv). The title compound was obtained in 11.10 g (87%) as a white solid. R = 0.34 (DCM 1: MeOH 0.1). H NMR (400 MHz; DMSO-d6): δ 10.53 (1H, br.s), 7.79 (1H, dd, J = 7.9, 1.7 Hz), 7.52 (1H, ddd, J = 8.1, 7.3, 1.7 Hz), 7.23 (1H, ddd, J = 7.9, 7.3, 1.2 Hz), 7.13 (1H, dd, J = 8.1, 1.2 Hz), 5.16 (1H, d, J = 4.2 Hz), 4.31 (1H, h, J = 4.4 Hz), 4.19 (1H, dd, J = 8.1, 5.8 Hz), 3.61 (1H, ddd, J = 12.1, 3.8, 1.2 Hz), 3.47 (1H, dd, J = 12.1, 4.8 Hz), 2.62 (1H, dt, J = 13.1, 5.5 Hz), 1.93 (1H, dddd, J = 13.0, 8.2, 4.6, 1.5 Hz). C{1H} NMR (100 MHz, DMSO-d6): δ 170.4, 165.1, 136.3, 132.2, 130.4, 126.0, 124.0, 121.3, 67.4, 55.2, 54.02 34.4. HRMS-ESI (m/z): [M + H] calculated for C12H13N2O3, 233.0926; found 233.0934. IR (νmax, film): 3383, 3235, 2941, 1691, 1622, 1480, 1445, 1415, 1090, 760 cm–1. [α] = 469° (c = 0.1, MeOH). MP = 225–226 °C (water/MeCN).

(2R,11aS)-7-Chloro-2-hydroxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-1b)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 1 started with 2-amino-5-chlorobenzoic acid (3.77 g, 22.024 mmol, 2 equiv). The title compound was obtained in 1.76 g (60%) as a white solid. R = 0.40 (DCM 1: MeOH 0.1). H NMR (400 MHz; DMSO-d6): δ 10.64 (1H, br.s), 7.74 (1H, d, J = 2.6 Hz), 7.59 (1H, dd, J = 8.7, 2.6 Hz), 7.15 (1H, d, J = 8.7 Hz), 5.16 (1H, d, J = 4.3 Hz), 4.31 (1H, h, J = 4.3 Hz), 4.25 (1H, dd, J = 8.1, 5.8 Hz), 3.61 (1H, ddd, J = 12.2, 3.8, 1.5 Hz), 3.48 (1H, dd, J = 12.2, 4.8 Hz), 2.62 (1H, dt, J = 13.1, 5.5 Hz), 1.94 (1H, dddd, J = 12.9, 8.0, 4.5, 1.4 Hz). C{1H} NMR (100 MHz, DMSO-d6): δ 170.2, 163.9, 135.3, 132.0, 129.6, 128.0, 127.4, 123.4, 67.4, 55.2, 54.1, 34.4. HRMS-ESI (m/z): [M + H] calculated for C12H12N2O3Cl, 267.0536; found 267.0545. IR (νmax, film): 3365, 3212, 3138, 2943, 1622, 1449, 1086, 813 cm–1. [α] = 440° (c = 0.1, MeOH). MP = 192–193 °C (water/MeCN).

(2R,11aS)-2-Hydroxy-8-(trifluoromethyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-1c)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 1 started with 2-amino-4-trifluoromethylbenzoic acid (2.93 g, 14.315 mmol, 2 equiv). The title compound was obtained in 0.93 g (43%) as a white solid. R = 0.42 (DCM 9: MeOH 1). H NMR (400 MHz; DMSO-d6): δ 10.75 (1H, br.s), 8.00 (1H, d, J = 8.2 Hz), 7.57 (1H, d, J = 8.2 Hz), 7.48 (1H, br.s), 5.20 (1H, br.s), 4.36–4.26 (2H, m), 3.63 (1H, dd, J = 12.2, 3.8 Hz), 3.50 (1H, dd, J = 12.2, 4.8 Hz), 2.62 (1H, dt, J = 13.1, 5.5 Hz), 1.95 (1H, m). C{1H} NMR (100 MHz, DMSO-d6) δ 170.4, 164.1, 137.0, 132.1, 132.0 (q, J = 32.1 Hz), 129.2, 123.5 (q, J = 273.0 Hz), 120.1 (q, J = 3.8 Hz), 118.2 (q, J = 3.8 Hz), 67.4, 55.2, 54.2, 34.4. HRMS-ESI (m/z): [M + H] calculated for C13H12N2O3F3, 301.0800; found 301.0811. IR (νmax, film): 3458, 3370, 3291, 2963, 2179, 1700, 1635, 1436, 1336, 1141, 667 cm–1. [α] = 369° (c = 0.1, MeOH). MP = 213–214 °C (water/MeCN).

(2R,11aS)-2-Hydroxy-9-methoxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-1d)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 1 started with 2-amino-3-methoxybenzoic acid (7.00 g, 41.846 mmol, 2 equiv). The title compound was obtained in 4.12 g (75%) as a white solid. R = 0.42 (DCM 9: MeOH 1). H NMR (400 MHz; DMSO-d6): δ 9.53 (1H, s), 7.38–7.31 (1H, m), 7.26–7.20 (2H, m), 5.14 (1H, d, J = 4.1 Hz), 4.32 (1H, h, J = 4.6 Hz), 4.17 (1H, dd, J = 8.1, 5.7 Hz), 3.85 (3H, s), 3.58 (1H, ddd, J = 12.2, 3.8, 1.5 Hz), 2.62 (1H, dt, J = 13.0, 5.5 Hz), 1.92 (1H, dddd, J = 13.0, 8.1, 4.6, 1.5 Hz). C{1H} NMR (100 MHz, DMSO-d6) δ 169.7, 164.8, 149.8, 127.6, 125.4, 124.8, 121.3, 113.7, 67.4, 56.2, 55.3, 53.9, 34.3. HRMS-ESI (m/z): [M + H] calculated for C13H15N2O4, 263.1032; found 263.1035. IR (νmax, film): 3406, 2961, 2840, 1684, 1442, 1260, 1071, 747, 600 cm–1. [α] = 500° (c = 0.1, MeOH). MP = 236–238 °C (water/MeCN).

(2R,11aS)-2-hydroxy-7,8-dimethoxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-1e)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 1 started with 2-amino-4,5-dimethoxybenzoic acid (5.21 g, 26.429 mmol, 2 equiv). The title compound was obtained in 1.73 g (45%) as a white solid. R = 0.21 (DCM 9: MeOH 1). H NMR (400 MHz; DMSO-d6): δ 10.28 (1H, br.s), 7.25 (1H, s), 6.69 (1H, s), 5.12 (1H, d, J = 4.1 Hz), 4.30 (1H, h, J = 4.5 Hz), 4.15 (1H, dd, J = 8.1, 6.0 Hz), 3.78 (3H, s), 3.77 (3H, s), 3.62 (1H, ddd, J = 12.0, 3.7, 1.4 Hz), 3.43 (1H, dd, J = 12.0, 4.8 Hz), 2.60 (1H, dt, J = 13.1, 5.5 Hz), 1.92 (1H, dddd, J = 12.9, 8.0, 4.5, 1.5 Hz). C{1H} NMR (100 MHz, DMSO-d6) δ 170.0, 165.0, 151.7, 145.3, 130.7, 117.8, 111.9, 104.4, 67.4, 55.6 (2 × C), 55.3, 54.0, 34.4. HRMS-ESI (m/z): [M + H] calculated for C14H17N2O5, 293.1137; found 293.1151. IR (νmax, film): 3429, 3245, 2990, 2836, 1677, 1609, 1519, 1434, 1264, 1011, 868, 624. [α] = 376° (c = 0.1, MeOH). MP = 170 °C (dec; water/MeCN).

(2R,11aS)-8-(Benzyloxy)-2-hydroxy-7-methoxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-1f)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 1 started with 2-amino-4-benzyloxy-5-methoxybenzoic acid (14.15 g, 51.785 mmol, 2 equiv). The title compound was obtained in 6.64 g (38%) as a beige solid. R = 0.34 (DCM 10: MeOH 1). H NMR (400 MHz; DMSO-d6): δ 10.31 (1H, s), 7.51–7.32 (5H, m), 7.27 (1H, s), 6.81 (1H, s), 5.15–5.02 (3H, m), 4.30 (1H, h, J = 4.5 Hz), 4.18–4.10 (1H, m), 3.79 (3H, s), 3.62 (1H, ddd, J = 12.0, 3.8, 1.4 Hz), 3.43 (1H, dd, J = 12.0, 4.8 Hz), 2.60 (1H, dt, J = 13.0, 5.5 Hz), 1.92 (1H, dddd, J = 13.0, 8.1, 4.5, 1.4 Hz). C{1H} NMR (100 MHz, DMSO-d6) δ 170.0, 164.9, 150.7, 145.5, 136.2, 130.6, 128.5, 128.2, 128.1, 118.1, 112.1, 105.7, 70.0, 67.4, 55.7, 55.3, 54.0, 34.4. HRMS-ESI (m/z): [M + H] calculated for C20H21N2O5, 369.1450; found 369.1455. IR (νmax, film): 3399, 3239, 2934, 1627, 1609, 1436, 1270, 1019, 730, 633 cm–1. [α] = 298° (c = 0.1, MeOH). MP = 158–159 °C (water/MeCN).

General Procedure for the Preparation of PBD Triones 10—Step 2

To a solution containing SI-1 (0.86 mmol, 1.0 equiv) and imidazole (175.9 mg, 2.58 mmol, 3.0 equiv) in anhydrous DMF (4 mL) at 0 °C was added TBSCl (389 mg, 2.58 mmol, 3.0 equiv). The mixture was warmed to rt and stirred for 16 h. Then, the reaction mixture was diluted with EtOAc (40 mL) and washed with water (4×30 mL). The organic extract was dried over Na2SO4, filtered, and evaporated, furnishing the title compound.

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-2a)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 2 started with SI-1a (200 mg, 0.860 mmol, 1 equiv). The title compound was obtained in 267 mg (89%) as a white solid. R = 0.32 (PE 1: EA 1). H NMR (400 MHz; CDCl3): δ 8.12 (1H, br.s), 8.01 (1H, dd, J = 8.0, 1.6 Hz), 7.48 (1H, ddd, J = 8.0, 7.3, 1.6 Hz), 7.29 (1H, ddd, J = 8.0, 7.3, 1.1 Hz), 6.99 (1H, dd, J = 8.0, 1.1 Hz), 4.54 (1H, p, J = 5.4 Hz), 4.22 (1H, dd, J = 8.2, 4.6 Hz), 3.72 (2H, qd, J = 12.0, 5.4 Hz), 2.85 (1H, dtd, J = 13.0, 5.4, 0.8 Hz), 2.08 (1H, dddd, J = 12.9, 8.1, 5.9, 0.8 Hz), 0.87 (9H, s), 0.10 (6H, s). C{1H} NMR (100 MHz, CDCl3): δ 171.0, 165.9, 135.1, 132.7, 131.6, 126.8, 125.5, 121.0, 69.4, 55.7, 54.4, 35.4, 25.9, 18.2, −4.6, −4.7. HRMS-ESI (m/z): [M + H] calculated for C18H27N2O3Si, 347.1791; found 347.1800. IR (νmax, film): 3235, 2954, 2928, 2857, 1695, 1623, 1481, 1251, 1131, 837, 759 cm–1. [α] = 328° (c = 0.1, CHCl3). MP = 194-195 °C (EtOAc).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-7-chloro-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-2b)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 2 started with SI-1b (1.50 g, 5.624 mmol, 1 equiv). The title compound was obtained in 1.87 g (87%) as a white solid. R = 0.42 (PE 1: EA 1). H NMR (400 MHz; CDCl3): δ 8.71 (1H, br.s), 7.98 (1H, d, J = 2.5 Hz), 7.43 (1H, dd, J = 8.5, 2.5 Hz), 6.97 (1H, d, J = 8.5 Hz), 4.52 (1H, p, J = 5.0 Hz), 4.21 (1H, dd, J = 8.1, 5.0 Hz), 3.71 (2H, d, J = 5.0 Hz), 2.84 (1H, dt, J = 13.1, 5.0 Hz), 2.08 (1H, ddd, J = 13.2, 8.1, 5.6 Hz), 0.87 (9H, s), 0.09 (6H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.9, 164.7, 133.7, 132.7, 131.2, 131.1, 128.0, 122.6, 69.3, 55.7, 54.6, 35.4, 25.9, 18.2, −4.6, −4.7. HRMS-ESI (m/z): [M + H] calculated for C18H26N2O3ClSi, 381.1401; found 381.1414. IR (νmax, film): 3227, 2954, 2857, 1700, 1644, 1481, 1438, 1252, 1128, 838, 776 cm–1. [α] = 327° (c = 0.1, CHCl3). MP = 177–178 °C (EtOAc).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-8-(trifluoromethyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-2c)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 2 started with SI-1c (0.878 g, 2.924 mmol, 1 equiv). The title compound was obtained in 915 mg (75%) as a white solid. R = 0.37 (PE 3: EA 1). H NMR (400 MHz; CDCl3): δ 8.58 (1H, br.s), 8.15 (1H, d, J = 9.2 Hz), 7.53 (1H, dd, J = 8.6, 1.4 Hz), 7.29 (1H, br.s), 4.54 (1H, p, J = 5.0 Hz), 4.23 (1H, dd, J = 8.1, 5.0 Hz), 3.73 (2H, d, J = 5.0 Hz), 2.86 (1H, dt, J = 13.1, 5.0 Hz), 2.11 (1H, ddd, J = 13.5, 8.1, 5.5 Hz), 0.87 (9H, s), 0.10 (6H, s). C{1H} NMR (100 MHz, CDCl3) δ 171.2, 164.8, 135.7, 134.5 (q, J = 33.2 Hz), 132.6, 129.5, 123.0 (q, J = 271.8 Hz), 121.8 (q, J = 3.5 Hz), 118.4 (q, J = 3.7 Hz), 69.3, 55.7, 54.6, 35.4, 25.8, 18.1, −4.8. HRMS-ESI (m/z): [M + H] calculated for C19H26N2O3F3Si, 415.1665; found 415.1661. IR (νmax, film): 3213, 2954, 2931, 2859, 1707, 1647, 1439, 1341, 1135, 838, 776 cm–1. [α] = 280° (c = 0.1, CHCl3). MP = 218–219 °C (EtOAc).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-9-methoxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-2d)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 2 started with SI-1d (3.40 g, 12.964 mmol, 1 equiv). The title compound was obtained in 4.85 g (99%) as a white solid. R = 0.43 (PE 1: EA 2). H NMR (400 MHz; CDCl3): δ 7.91 (1H, br.s), 7.57 (1H, dd, J = 8.0, 1.4 Hz), 7.20 (1H, t, J = 8.0 Hz), 7.02 (1H, dd, J = 8.0, 1.4 Hz), 4.53 (1H, p, J = 5.4 Hz), 4.19 (1H, dd, J = 8.2, 4.5 Hz), 3.90 (3H, s), 3.74 (1H, dd, J = 12.0, 5.4 Hz), 3.68 (1H, dd, J = 12.0, 5.4 Hz), 2.85 (1H, dddd, J = 13.0, 5.4, 4.5, 1.0 Hz), 2.06 (1H, dddd, J = 13.0, 8.2, 6.0, 1.0 Hz), 0.87 (9H, s), 0.09 (6H, s). C{1H} NMR (100 MHz, CDCl3) δ 170.4, 165.8, 148.6, 126.8, 125.2, 125.0, 122.7, 112.9, 69.3, 56.2, 55.9, 54.4, 35.4, 25.9, 18.1, −4.7. HRMS-ESI (m/z): [M + H] calculated for C19H29N2O4Si, 377.1897; found 377.1895. IR (νmax, film): 3385, 3237, 2953, 2857, 1702, 1636, 1413, 1260, 1130, 754 cm–1. [α] = 312° (c = 0.1, CHCl3).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-7,8-dimethoxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-2e)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 2 started with SI-1e (1.70 g, 5.816 mmol, 1 equiv). The title compound was obtained in 2.09 g (88%) as a white solid. R = 0.25 (PE 1: EA 2). H NMR (400 MHz; CDCl3): δ 8.46 (1H, br.s), 7.44 (1H, s), 6.47 (1H, s), 4.52 (1H, p, J = 5.6 Hz), 4.20 (1H, dd, J = 8.2, 4.3 Hz), 3.93 (3H, s), 3.90 (3H, s), 3.73 (1H, dd, J = 11.9, 5.5 Hz), 3.65 (1H, dd, J = 11.9, 5.5 Hz), 2.83 (1H, dt, J = 12.8, 5.0 Hz), 2.05 (1H, m), 0.87 (9H, s), 0.09 (6H, s). C{1H} NMR (100 MHz, CDCl3) δ 170.9, 165.8, 152.5, 146.7, 129.5, 118.9, 112.5, 103.9, 69.4, 56.4, 56.3, 55.8, 54.3, 35.3, 25.9, 18.2, −4.7 (2 × C). HRMS-ESI (m/z): [M + H] calculated for C20H31N2O5Si, 407.2002; found 407.2009. IR (νmax, film): 3273, 2928, 2856, 1699, 1606, 1495, 1258, 1121, 838, 776, 651 cm–1. [α] = 273° (c = 0.1, CHCl3). MP = 268–269 °C (EtOAc).

(2R,11aS)-8-(Benzyloxy)-2-((tert-butyldimethylsilyl)oxy)-7-methoxy-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-2f)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 2 started with SI-1f (6.39 g, 17.346 mmol, 1 equiv). The title compound was obtained in 6.42 g (76%) as a white solid. R = 0.46 (PE 1: EA 2). H NMR (600MHz; CDCl3): δ 8.36 (1H, br.s), 7.47–7.28 (6H, m), 6.48 (1H, s), 5.16 (2H, dd, J = 19.2, 12.3 Hz), 4.51 (1H, p, J = 5.4 Hz), 4.17 (1H, dd, J = 8.2, 4.5 Hz), 3.92 (3H, s), 3.68 (2H, qd, J = 12.0, 5.4 Hz), 2.81 (1H, dt, J = 12.9, 5.0 Hz), 2.04 (1H, m), 0.87 (9H, s), 0.09 (6H, s). C{1H} NMR (150 MHz, CDCl3) δ 170.8, 165.8, 151.5, 147.2, 136.0, 129.3, 128.9, 128.4, 127.4, 119.2, 112.8, 106.0, 71.2, 69.4, 56.4, 55.8, 54.3, 35.3, 25.9, 18.1, −4.7. HRMS-ESI (m/z): [M + H] calculated for C26H35N2O5Si, 483.2315; found 483.2321. IR (νmax, film): 3220, 2953, 1700, 1609, 1517, 1430, 1254, 1121, 1005, 836, 778 cm–1. [α] = 189° (c = 0.1, CHCl3).

General Procedure for the Preparation of PBD Triones 10—Step 3

To a stirred suspension of NaH (60% in mineral oil, 101.6 mg, 2.54 mmol, 1.1 equiv; washed twice with dry THF before the reaction) in THF (5 mL, freshly distilled over Na/Ph2CO) was added a solution of SI-2 (2.308 mmol, 1.0 equiv) in dry THF (15 mL) at 0 °C, and the mixture was stirred until hydrogen evolution ceased (approx. 15 min). Then, to the reaction mixture was added a solution of SEMCl (1.1 mL, 5.771 mmol, 2.5 equiv) in dry THF (5 mL), and stirring was continued for 16 h at rt. Next, the suspension was cooled (ice bath), quenched with water (50 mL), extracted with DCM (2 × 50 mL), and dried (Na2SO4). Volatiles were evaporated, and the residue was purified on silica gel (PE/EtOAc). The product-containing fractions were combined and evaporated in vacuo, furnishing the title compound.

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-3a)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 3 started with SI-2a (800 mg, 2.308 mmol, 1 equiv). The title compound was obtained in 920 mg (83%) as colorless oil. R = 0.41 (PE 2: EA 1). H NMR (400 MHz; CDCl3): δ 7.91 (1H, dd, J = 7.8, 1.7 Hz), 7.67 (1H, dd, J = 8.2, 0.9 Hz), 7.52 (1H, ddd, J = 8.2, 7.3, 1.7 Hz), 7.34 (1H, ddd, J = 7.8, 7.3, 1.1 Hz), 5.50 (1H, d, J = 9.9 Hz), 4.73 (1H, d, J = 9.9 Hz), 4.59 (1H, p, J = 5.8 Hz), 4.22 (1H, dd, J = 8.1, 3.9 Hz), 3.80–3.70 (2H, m), 3.65 (1H, ddd, J = 9.6, 8.7, 7.8 Hz), 3.56 (1H, dd, J = 11.7, 5.5 Hz), 2.86 (1H, ddd, J = 12.2, 5.0, 3.9 Hz), 2.03 (1H, dddd, J = 13.0, 8.2, 6.4, 0.9 Hz), 0.98 (2H, dd, J = 8.8, 7.9 Hz), 0.87 (9H, s), 0.09 (6H, s), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.1, 165.9, 139.8, 132.5, 130.3, 129.3, 126.5, 122.7, 78.1, 69.7, 67.1, 56.5, 53.8, 35.7, 25.9, 18.4, 18.1, −1.3, −4.7. HRMS-ESI (m/z): [M + H] calculated for C24H41N2O4Si2, 477.2605; found 477.2614. IR (νmax, film): 2953, 2857, 1690, 1652, 1461, 1411, 1250, 1129, 1072, 861, 837, 777, 762, 709 cm–1. [α] = 237° (c = 0.1, CHCl3).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-7-chloro-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-3b)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 3 started with SI-2b (1.80 g, 4.725 mmol, 1 equiv). The title compound was obtained in 1.60 g (66%) as a colorless oil. R = 0.48 (PE 3: EA 1). H NMR (400 MHz; CDCl3): δ 7.88 (1H, d, J = 2.6 Hz), 7.64 (1H, d, J = 8.8 Hz), 7.47 (1H, dd, J = 8.8, 2.6 Hz), 5.50 (1H, d, J = 9.9 Hz), 4.66 (1H, d, J = 9.9 Hz), 4.57 (1H, p, J = 5.5 Hz), 4.21 (1H, dd, J = 8.1, 4.1 Hz), 3.77–3.61 (3H, m), 3.57 (1H, dd, J = 11.9, 5.0 Hz), 2.86 (1H, m), 2.04 (1H, m), 0.98 (2H, m), 0.87 (9H, s), 0.09 (6H, s), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.7, 164.6, 138.31, 132.5, 132.3, 130.6, 130.1, 124.2, 78.1, 69.6, 67.2, 56.5, 54.0, 35.7, 25.9, 18.4, 18.1, −1.3, −4.7. HRMS-ESI (m/z): [M + H] calculated for C24H40N2O4ClSi2, 511.2215; found 511.2227. IR (νmax, film): 2953, 2858, 1695, 1652, 1441, 1363, 1250, 1071, 836, 776 cm–1. [α] = 230° (c = 0.1, CHCl3).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-8-(trifluoromethyl)-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-3c)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 3 started with SI-2c (900 mg, 2.171 mmol, 1 equiv). The title compound was obtained in 623 g (52%) as colorless oil. R = 0.53 (PE 3: EA 1). H NMR (400 MHz; CDCl3): δ 8.03 (1H, d, J = 8.2 Hz), 8.01 (1H, br.s), 7.58 (1H, ddd, J = 8.2, 1.8, 0.7 Hz), 5.55 (1H, d, J = 10.0 Hz), 4.70 (1H, d, J = 10.0 Hz), 4.58 (1H, p, J = 5.4 Hz), 4.22 (1H, dd, J = 8.1, 4.3 Hz), 3.82–3.64 (3H, m), 3.61 (1H, ddd, J = 12.3, 5.0, 1.0 Hz), 2.87 (1H, dt, J = 13.0, 4.9 Hz), 2.10–2.01 (1H, m), 0.98 (2H, m), 0.86 (9H, s), 0.09 (6H, s), 0.03 (9, s). C{1H} NMR (100 MHz, CDCl3): δ 169.7, 164.7, 140.2, 134.4 (q, J = 33.0 Hz), 132.1, 131.3, 123.2 (q, J = 274.5 Hz), 123.1 (q, J = 3.6 Hz), 120.0 (q, J = 3.6 Hz), 78.0, 69.6, 67.5, 56.5, 54.1, 35.8, 25.8, 18.3, 18.1, −1.3, −4.7 (2 × C). HRMS-ESI (m/z): [M + H] calculated for C25H40N2O4F3Si2, 545.2479; found 545.2476. IR (νmax, film): 2954, 2930, 2896, 2859, 1699, 1656, 1447, 1319, 1251, 1133, 1070, 838 cm–1. [α] = 219° (c = 0.1, CHCl3).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-9-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-3d)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 3 started with SI-2d (5.09 g, 13.518 mmol, 1 equiv). The title compound was obtained in 6.70 g (97%) as colorless oil. R = 0.45 (PE 1: EA 1). H NMR (400 MHz; CDCl3): δ 7.48 (1H, dd, J = 7.9, 1.4 Hz), 7.35 (1H, t, J = 7.9 Hz), 7.07 (1H, dd, J = 7.9, 1.4 Hz), 5.72 (1H, d, J = 10.5 Hz), 4.96 (1H, d, J = 10.5 Hz), 4.62 (1H, p, J = 5.7 Hz), 4.16 (1H, dd, J = 8.0, 3.8 Hz), 3.88 (3H, s), 3.78 (1H, dd, J = 12.0, 6.0 Hz), 3.50 (1H, dd, J = 12.0, 5.5 Hz), 3.39–3.27 (2H, m), 2.84 (1H, ddd, J = 12.3, 5.7, 3.5 Hz), 2.01–1.92 (1H, m), 0.86 (9H, s), 0.83–0.65 (2H, m), 0.08 (6H, s), −0.07 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.9, 165.4, 152.8, 133.6, 128.2, 126.7, 121.6, 114.4, 75.2, 69.8, 66.3, 56.9, 56.0, 53.5, 35.4, 25.9, 18.1, 17.9, −1.4, −4.7. HRMS-ESI (m/z): [M + Na] calculated for C25H42N2O5Si2Na, 529.2530; found 529.2541. IR (νmax, film): 2952, 1652, 1410, 1258, 1075, 837 cm–1. [α] = 116° (c = 0.1, CHCl3).

(2R,11aS)-2-((tert-Butyldimethylsilyl)oxy)-7,8-dimethoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-3e)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 3 started with SI-2e (100 mg, 0.246 mmol, 1 equiv). The title compound was obtained in 126 mg (95%) as colorless oil. R = 0.52 (PE 1: EA 1). H NMR (400 MHz; CDCl3): δ 7.34 (1H, s), 7.23 (1H, s), 5.52 (1H, d, J = 9.9 Hz), 4.64 (1H, d, J = 9.9 Hz), 4.58 (1H, p, J = 5.7 Hz), 4.23 (1H, dd, J = 7.9, 3.9 Hz), 3.94 (3H, s), 3.91 (3H, s), 3.83–3.63 (3H, m), 3.55 (1H, dd, J = 11.8, 5.7 Hz), 2.85 (1H, ddd, J = 12.2, 5.2, 3.8 Hz), 2.06–1.98 (1H, m), 0.98 (2H, m), 0.87 (9H, s), 0.10 (6H, s), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.1, 165.8, 152.0, 147.3, 134.1, 121.6, 111.4, 105.6, 78.2, 69.7, 67.2, 56.7, 56.3 (2 × C), 53.8, 35.6, 25.9, 18.5, 18.2, −1.2, −4.7. HRMS-ESI (m/z): [M + H] calculated for C26H45N2O6Si2, 537.2816; found 537.2838. IR (νmax, film): 2952, 2857, 1684, 1652, 1517, 1456, 1434, 1361, 1249, 1130, 1069, 836, 777 cm–1. [α] = 209° (c = 0.1, CHCl3).

(2R,11aS)-8-(Benzyloxy)-2-((tert-butyldimethylsilyl)oxy)-7-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-3f)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 3 started with SI-2f (6.40 g, 13.260 mmol, 1 equiv). The title compound was obtained in 7.62 g (93%) as colorless oil. R = 0.39 (PE 2: EA 1). H NMR (400 MHz; CDCl3): δ 7.46–7.40 (2H, m), 7.40–7.28 (4H, m), 7.24 (1H, br.s), 5.42 (1H, d, J = 9.8 Hz), 5.20 (2H, m), 4.56 (1H, p, J = 5.8 Hz), 4.47 (1H, d, J = 9.8 Hz), 4.20 (1H, dd, J = 8.2, 3.9 Hz), 3.94 (3H, s), 3.77–3.63 (2H, m), 3.64–3.49 (2H, m), 2.83 (1H, m), 2.00 (1H, m), 0.95 (2H, m), 0.86 (9H, s), 0.09 (6H, s), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.0, 165.7, 150.9, 147.7, 136.1, 133.8, 128.8, 128.3, 127.5, 121.8, 111.7, 107.8, 78.1, 71.0, 69.7, 67.0, 56.6, 56.4, 53.7, 35.6, 25.9, 18.5, 18.1, −1.2, −4.7. HRMS-ESI (m/z): [M + H] calculated for C32H49N2O6Si2, 613.3129; found 613.3140. IR (νmax, film): 3447, 2953, 2894, 1689, 1641, 1463, 1361, 1249, 1129, 1069, 836, 776 cm–1. [α] = 189° (c = 0.1, CHCl3).

General Procedure for the Preparation of PBD Triones 10—Step 4

To a stirred solution of SI-3 (2.936 mmol, 1.0 equiv) in THF (60 mL) was added TBAF trihydrate (1.43 g, 4.404 mmol, 1.5 equiv) at 0 °C, and the mixture was stirred for 3 h at room temperature. Then, volatiles were evaporated in vacuo and the residual oil was purified on silica gel (EtOAc:EtOH). The product-containing fractions were combined and evaporated in vacuo furnishing the title compound.

(2R,11aS)-2-Hydroxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-4a)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 4 started with SI-3a (1.40 g, 2.936 mmol, 1.0 equiv). The title compound was obtained in 893 mg (84%) as colorless oil. R = 0.43 (EA 1: EtOH 0.05). H NMR (400 MHz; CDCl3): δ 7.87 (1H, dd, J = 7.8, 1.7 Hz), 7.68 (1H, dd, J = 8.2, 1.2 Hz), 7.52 (1H, ddd, J = 8.2, 7.3, 1.7 Hz), 7.32 (1H, td, J = 7.8, 1.2 Hz), 5.50 (1H, d, J = 9.8 Hz), 4.74 (1H, d, J = 9.8 Hz), 4.67 (1H, m), 4.30 (1H, dd, J = 8.1, 5.6 Hz), 3.87 (1H, ddd, J = 12.7, 3.5, 1.6 Hz), 3.79–3.61 (3H, m), 2.99 (1H, dt, J = 13.6, 5.5 Hz), 2.18 (1H, d, J = 3.7 Hz), 2.13 (1H, dddd, J = 13.6, 8.1, 4.2, 1.6 Hz), 0.99 (2H, m), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.8, 166.0, 139.8, 132.6, 130.4, 129.1, 126.6, 122.8, 78.2, 69.5, 67.1, 56.4, 54.1, 35.2, 18.4, −1.3. HRMS-ESI (m/z): [M + Na] calculated for C18H26N2O4SiNa, 385.1560; found 385.1558. IR (νmax, film): 3393, 2952, 2895, 1694, 1634, 1463, 1249, 1076, 763 cm–1. [α] = 275° (c = 0.1, CHCl3).

(2R,11aS)-7-Chloro-2-hydroxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-4b)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 4 starting from SI-3b (1.60 g, 3.130 mmol, 1.0 equiv). The title compound was obtained in 1.15 g (93%) as colorless foam. R = 0.47 (EA 100: EtOH 1). H NMR (400 MHz; CDCl3): δ 7.81 (1H, d, J = 2.5 Hz), 7.66 (1H, d, J = 8.7 Hz), 7.47 (1H, dd, J = 8.7, 2.5 Hz), 5.51 (1H, d, J = 9.9 Hz), 4.68 (1H, d, J = 9.9 Hz), 4.66 (1H, m), 4.31 (1H, dd, J = 8.1, 6.0 Hz), 3.89 (1H, ddd, J = 12.8, 3.1, 1.7 Hz), 3.78–3.61 (3H, m), 2.98 (1H, dt, J = 13.7, 5.6 Hz), 2.24 (1H, br.s), 2.16 (1H, dddd, J = 13.7, 8.1, 3.8, 1.8 Hz), 0.98 (2H, m), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.4, 164.8, 138.3, 132.6, 132.4, 130.4, 130.1, 124.3, 78.2, 69.4, 67.3, 56.4, 54.3, 35.2, 18.4, −1.3. HRMS-ESI (m/z): [M + Na] calculated for C18H25N2O4SiClNa, 419.1170; found 419.1165. IR (νmax, film): 3404, 2953, 2894, 1694, 1639, 1444, 1362, 1249, 1075, 836 cm–1. [α] = 274° (c = 0.1, CHCl3). MP = 60–61 °C (EtOAc:EtOH).

(2R,11aS)-2-Hydroxy-8-(trifluoromethyl)-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-4c)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 4 started with SI-3c (620 mg, 1.138 mmol, 1.0 equiv). The title compound was obtained in 325 mg (66%) as colorless foam. R = 0.37 (EA 100: EtOH 1). H NMR (400 MHz; CDCl3): δ 8.01 (1H, br.s), 7.99 (1H, d, J = 8.2 Hz), 7.57 (1H, dd, J = 8.2, 1.1 Hz), 5.56 (1H, d, J = 10.0 Hz), 4.71 (1H, d, J = 10.0 Hz), 4.67 (1H, m), 4.29 (1H, dd, J = 8.0, 5.9 Hz), 3.89 (1H, ddd, J = 12.7, 3.2, 1.6 Hz), 3.84–3.73 (1H, m), 3.72–3.62 (2H, m), 2.99 (1H, dt, J = 13.7, 5.5 Hz), 2.35 (1H, d, J = 3.7 Hz), 2.16 (1H, dddd, J = 13.7, 8.1, 3.9, 1.7 Hz), 1.04–0.94 (2H, m), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.4, 164.9, 140.2, 134.5 (q, J = 33.0 Hz), 131.9, 131.3, 123.2 (q, J = 275.1 Hz), 123.1 (q, J = 3.6 Hz), 120.0 (q, J = 3.6 Hz), 78.1, 69.3, 67.5, 56.4, 54.3, 35.2, 18.3, −1.3. HRMS-ESI (m/z): [M + Na] calculated for C19H25N2O4SiF3Na, 453.1433; found 453.1429. IR (νmax, film): 3392, 2954, 1702, 1639, 1321, 1174, 1133, 1083, 860, 838 cm–1. [α] = 256° (c = 0.1, CHCl3).

(2R,11aS)-2-Hydroxy-9-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-4d)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 4 started with SI-3d (6.70 g, 13.220 mmol, 1.0 equiv). The title compound was obtained in 3.41 g (65%) as colorless foam. R = 0.38 (EA 20: EtOH 1). H NMR (400 MHz; CDCl3): δ 7.41 (1H, dd, J = 7.9, 1.5 Hz), 7.31 (1H, t, J = 8.0 Hz), 7.06 (1H, dd, J = 8.0, 1.5 Hz), 5.70 (1H, d, J = 10.4 Hz), 4.95 (1H, d, J = 10.4 Hz), 4.63 (1H, h, J = 4.6 Hz), 4.22 (1H, dd, J = 8.2, 5.5 Hz), 3.87 (3H, s), 3.81 (1H, ddd, J = 12.6, 3.5, 1.6 Hz), 3.63 (1H, dd, J = 12.6, 4.8 Hz), 3.38–3.24 (2H, m), 3.08 (1H, d, J = 3.8 Hz), 2.93 (1H, dt, J = 13.5, 5.4 Hz), 2.04 (1H, dddd, J = 13.7, 8.2, 4.2, 1.6 Hz), 0.81–0.61 (2H, m), −0.10 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.6, 165.6, 152.7, 133.3, 128.2, 126.7, 121.6, 114.5, 75.3, 69.4, 66.3, 56.8, 56.0, 53.8, 34.7, 17.9, −1.4. HRMS-ESI (m/z): [M + Na] calculated for C19H28N2O5SiNa, 415.1665; found 415.1663. [α] = 133° (c = 0.1, CHCl3). MP = 159–160 °C (EtOAc:EtOH).

(2R,11aS)-2-Hydroxy-7,8-dimethoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-4e)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 4 started with SI-3e (573 mg, 1.067 mmol, 1.0 equiv). The title compound was obtained in 305 mg (68%) as colorless foam. R = 0.31 (EA 20: EtOH 1). H NMR (400 MHz; CDCl3): δ 7.32 (1H, s), 7.23 (1H, s), 5.52 (1H, d, J = 9.9 Hz), 4.64 (1H, d, J = 9.9 Hz overlapping with 1H, m), 4.30 (1H, dd, J = 8.1, 5.6 Hz), 3.90 (6H, br.s), 3.87 (1H, ddd, J = 12.5, 3.6, 1.6 Hz), 3.79 (1H, m), 3.71–3.60 (2H, m), 2.96 (1H, dt, J = 13.5, 5.5 Hz), 2.52 (1H, br.s), 2.12 (1H, m), 0.98 (2H, m), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.8, 166.0, 152.1, 147.2, 134.1, 121.3, 111.4, 105.6, 78.3, 69.4, 67.2, 56.6, 56.3, 56.2, 54.0, 35.1, 18.5, −1.2. HRMS-ESI (m/z): [M + H] calculated for C20H31N2O6Si, 423.1951; found 423.1956. IR (νmax, film): 3379, 2954, 1683, 1634, 1519, 1456, 1436, 1360, 1249, 1062, 861, 837, 756 cm–1. [α] = 258° (c = 0.1, CHCl3).

(2R,11aS)-8-(Benzyloxy)-2-hydroxy-7-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (SI-4f)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 4 started with SI-3e (7.60 g, 12.400 mmol, 1.0 equiv). The title compound was obtained in 5.22 g (84%) as a white solid. R = 0.41 (EA 20: EtOH 1). H NMR (400 MHz; CDCl3): δ 7.43 (2H, m), 7.38–7.28 (4H, m), 7.24 (1H, s), 5.42 (1H, d, J = 9.8 Hz), 1.98 (2H, s), 4.62 (1H, m), 4.49 (1H, d, J = 9.8 Hz), 4.27 (1H, dd, J = 8.1, 5.6 Hz), 3.91 (3H, s), 3.86 (1H, ddd, J = 12.5, 3.6, 1.5 Hz), 3.75–3.54 (3H, m), 2.94 (1H, dt, J = 13.6, 5.4 Hz), 2.47 (1H, d, J = 3.6 Hz), 2.10 (1H, dddd, J = 13.8, 8.1, 4.4, 1.6 Hz), 0.96 (2H, m), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.7, 165.9, 151.0, 147.7, 136.1, 133.9, 128.8, 128.3, 127.5, 121.5, 111.7, 107.8, 78.2, 71.0, 69.4, 67.1, 56.5, 56.3, 54.0, 35.1, 18.5, −1.2. IR (νmax, film): 3378, 2952, 1683, 1626, 1466, 1361, 1248, 1060, 836, 755 cm–1. HRMS-ESI (m/z): [M + H] calculated for C26H35N2O6Si, 499.2264; found 499.2286. [α] = 245° (c = 0.1, CHCl3). MP = 69–70 °C (EtOAc:EtOH).

General Procedure for the Preparation of PBD Triones 10—Step 5

To a solution of SI-4 (16.827 mmol, 1.0 equiv) in anhydrous DCM (200 mL) was added DMP (11.0, 25.241 mmol, 1.5 equiv) at room temperature, and the reaction was stirred for 16 h. Then, sat. aqueous Na2S2O3 solution (100 mL) was added, the organic layer was separated and the aqueous phase was extracted with DCM (2 × 100 mL). Combined organic extracts were washed with sat. NaHCO3 (200 mL) and brine (100 mL) and dried (Na2SO4). Volatiles were evaporated, and the residue was purified on silica gel (PE/EtOAc). The product-containing fractions were combined and evaporated in vacuo, furnishing the title compound.

(S)-10-((2-(Trimethylsilyl)ethoxy)methyl)-1,11a-dihydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-2,5,11(3H,10H)-trione (10a)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 5 started with SI-4a (6.10 g, 16.827 mmol, 1.0 equiv). The title compound was obtained in 5.30 g (87%) as colorless foam. R = 0.45 (PE 1: EA 2). H NMR (400 MHz; CDCl3): δ 7.91 (1H, dd, J = 7.8, 1.7 Hz), 7.72 (1H, dd, J = 8.3, 1.2 Hz), 7.59 (1H, ddd, J = 8.3, 7.3, 1.7 Hz), 7.40 (1H, ddd, J = 8.7, 7.8, 1.2 Hz), 5.53 (1H, d, J = 9.9 Hz), 4.79 (1H, d, J = 9.9 Hz), 4.63 (1H, dd, J = 9.9, 3.0 Hz), 4.22 (1H, br.d, J = 19.9 Hz), 3.92 (1H, br.d, J = 19.9 Hz), 3.78–3.61 (2H, m), 3.61–3.54 (1H, m), 2.79 (1H, ddd, J = 9.9, 1.5, 0.5 Hz), 0.98 (2H, m), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 206.7, 168.9, 166.2, 139.8, 133.1, 130.3, 128.4, 127.1, 123.0, 78.3, 67.3, 54.8, 52.3, 37.5, 18.4, −1.3. HRMS-ESI (m/z): [M – H] calculated for C18H23N2O4Si, 359.1427; found 359.1436. IR (νmax, film): 3463, 2950, 1765, 1688, 1648, 1462, 1410, 1248, 1075, 837 cm–1. [α] = 361° (c = 0.1, CHCl3).

(S)-7-Chloro-10-((2-(trimethylsilyl)ethoxy)methyl)-1,11a-dihydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-2,5,11(3H,10H)-trione (10b)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 5 started with SI-4b (1.10 g, 2.771 mmol, 1.0 equiv). The title compound was obtained in 933 mg (85%) as colorless foam. R = 0.58 (PE 1: EA 1). H NMR (400 MHz; CDCl3): δ 7.89 (1H, d, J = 2.4 Hz), 7.70 (1H, d, J = 8.8 Hz), 7.54 (1H, dd, J = 8.8, 2.4 Hz), 5.54 (1H, d, J = 10.0 Hz), 4.73 (1H, d, J = 10.0 Hz), 4.62 (1H, dd, J = 10.0, 3.0 Hz), 4.22 (1H, br.d, J = 20.0 Hz), 3.92 (1H, br.d, J = 20.0 Hz), 3.78–3.62 (2H, m), 3.58 (1H, m), 2.80 (1H, ddd, J = 10.8, 10.0, 1.2 Hz), 0.98 (2H, m), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 206.2, 168.6, 164.9, 138.3, 133.1, 132.9, 130.1, 129.7, 124.5, 78.2, 67.5, 54.8, 52.4, 37.4, 18.4, −1.3. HRMS-ESI (m/z): [M + Na] calculated for C18H23N2O4ClSiNa, 417.1013; found 417.1024. IR (νmax, film): 2953, 2897, 1768, 1694, 1653, 1448, 1367, 1248,1071, 835, 754 cm–1. [α] = 377° (c = 0.1, CHCl3). MP = 58–59 °C (PE/EtOAc).

(S)-8-(Trifluoromethyl)-10-((2-(trimethylsilyl)ethoxy)methyl)-1,11a-dihydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-2,5,11(3H,10H)-trione (10c)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 5 started with SI-4c (308 mg, 0.715 mmol, 1.0 equiv). The title compound was obtained in 165 mg (53%) as colorless foam. R = 0.24 (PE 2: EA 1). H NMR (400 MHz; CDCl3): δ 8.04 (2H, m), 7.65 (1H, dd, J = 8.1, 1.2 Hz), 5.60 (1H, d, J = 10.0 Hz), 4.77 (1H, d, J = 10.0 Hz), 4.62 (1H, dd, J = 9.9, 3.1 Hz), 4.24 (1H, m), 3.94 (1H, m), 3.84–3.55 (3H, m), 2.82 (1H, ddd, J = 11.0, 9.5, 1.2 Hz), 0.99 (2H, m), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 206.0, 168.5, 165.0, 140.3, 135.0 (q, J = 34.0 Hz), 131.4, 131.2, 123.6 (q, J = 3.5 Hz), 123.0 (q, J = 273.0 Hz), 120.2 (q, J = 3.5 Hz), 78.2, 67.7, 54.8, 52.4, 37.4, 18.3, −1.3. HRMS-ESI (m/z): [M + Na] calculated for C19H23N2O4SiF3Na, 451.1277; found 451.1288. IR (νmax, film): 2954, 2898, 1768, 1697, 1651, 1446, 1321, 1132, 839 cm–1. [α] = 280° (c = 0.1, CHCl3).

(S)-9-Methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,11a-dihydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-2,5,11(3H,10H)-trione (10d)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 5 started with SI-4d (3.41 g, 8.687 mmol, 1.0 equiv). The title compound was obtained in 3.21 g (94%) as colorless foam. R = 0.31 (ether). H NMR (400 MHz; CDCl3): δ 7.47 (1H, dd, J = 7.9, 1.5 Hz), 7.40 (1H, dd, J = 8.2, 7.9 Hz), 7.13 (1H, dd, J = 8.2, 1.5 Hz), 5.72 (1H, d, J = 10.5 Hz), 5.02 (1H, d, J = 10.5 Hz), 4.57 (1H, dd, J = 9.7, 2.8 Hz), 4.17 (1H, d, J = 19.6 Hz), 3.91 (3H, s), 3.88 (1H, d, J = 19.6 Hz, overlapping with 3H of MeO), 3.55–3.46 (1H, m), 3.40–3.28 (2H, m), 2.71 (1H, ddd, J = 10.9, 9.7, 1.2 Hz), 0.84–0.64 (2H, m), −0.09 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 206.9, 169.6, 165.8, 152.9, 132.6, 128.8, 126.6, 121.5, 114.9, 75.4, 66.6, 56.1, 55.2, 52.1, 37.3, 18.0, −1.3. HRMS-ESI (m/z): [M + Na] calculated for C19H26N2O5SiNa, 413.1509; found 413.1522. IR (νmax, film): 3395, 2952, 1627, 1444, 1248, 1074, 836, 754 cm–1. [α] = 182° (c = 0.1, CHCl3).

(S)-7,8-Dimethoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,11a-dihydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-2,5,11(3H,10H)-trione (10e)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 5 started with SI-4e (205 mg, 0.674 mmol, 1.0 equiv). The title compound was obtained in 208 mg (73%) as colorless foam. R = 0.25 (PE 1: EA 2). H NMR (400 MHz; CDCl3): δ 7.33 (1H, br.s), 7.26 (1H, br.s), 5.55 (1H, d, J = 9.9 Hz), 4.70 (1H, d, J = 9.9 Hz), 4.64 (1H, dd, J = 9.9, 3.1 Hz), 4.24 (1H, d, J = 20.1 Hz), 3.95 (3H, s), 3.92 (3H, s), 3.90 (1H, d, J = 20.1 Hz), 3.79 (1H, td, J = 9.7, 6.8 Hz), 3.68 (1H, td, J = 9.7, 6.8 Hz), 3.58 (1H, m), 2.79 (1H, ddd, J = 11.3, 9.9, 1.2 Hz), 0.98 (2H, m), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 206.9, 168.9, 166.1, 152.5, 147.7, 134.1, 120.6, 111.2, 105.7, 78.4, 67.4, 56.4, 56.4, 54.9, 52.4, 37.5, 18.5, −1.2. HRMS-ESI (m/z): [M + Na] calculated for C20H28N2O6SiNa, 443.1614; found 443.1606. IR (νmax, film): 2953, 1766, 1687, 1645, 1608, 1519, 1436, 1360, 1251, 1069, 1014, 838, 761 cm–1. [α] = 344° (c = 0.1, CHCl3).

(S)-8-(Benzyloxy)-7-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,11a-dihydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-2,5,11(3H,10H)-trione (10f)

Prepared according to the general procedure for the preparation of PBD triones 10. Step 5 started with SI-4f (5.20 g, 10.428 mmol, 1.0 equiv). The title compound was obtained in 3.08 g (59%) as colorless foam. R = 0.39 (PE 1: EA 2). H NMR (400 MHz; CDCl3): δ 7.46–7.42 (2H, m), 7.41–7.32 (4H, m), 7.28 (1H, s), 5.46 (1H, d, J = 9.9 Hz), 5.22 (2H, dd, J = 14.3, 12.6 Hz), 4.61 (1H, dd, J = 9.9, 3.2 Hz), 4.54 (1H, d, J = 9.9 Hz), 4.23 (1H, m), 3.95 (3H, s), 3.88 (1H, m), 3.74–3.51 (3H, m), 2.77 (1H, ddd, J = 11.0, 9.9, 1.2 Hz), 0.87–0.81 (2H, m), 0.04 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 206.9, 168.8, 166.0, 151.4, 148.2, 135.9, 133.9, 128.9, 128.5, 127.6, 120.7, 111.6, 107.9, 78.3, 71.1, 67.3, 56.4, 54.9, 52.4, 37.4, 18.5, −1.2. HRMS-ESI (m/z): [M + H] calculated for C26H33N2O6Si, 497.2108; found 497.2090. IR (νmax, film): 2952, 1766, 1688, 1646, 1435, 1249, 1068, 837, 754 cm–1. [α] = 290° (c = 0.1, CHCl3).

General Procedure for the Preparation of Julia–Kocienski Reagents 11—Step 1

To a solution of isothiocyanate (39.845 mmol, 1.0 equiv) in iPrOH (40 mL), sodium azide (5.2 g, 79.691 mmol, 2.0 equiv) and water (65 mL) were added subsequentially, and the resulting mixture was heated in a sealed tube at 100 °C for 5 h. Then, the reaction was cooled to ambient temperature, quenched with 3N HCl (60 mL), partially evaporated (∼1/2 of the initial volume), and extracted with DCM (3 × 40 mL). The combined organic extracts were dried (Na2SO4), filtered, and evaporated in vacuo, furnishing the title compound. The obtained material was used in the next step without further purification.

1-(4-Methoxyphenyl)-1H-tetrazole-5-thiol (SI-5b)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 1 started with 1-isothiocyanato-4-methoxybenzene (9.56 g, 57.913 mmol, 1.0 equiv). The product was used in the next step without further purification.

1-(4-Cyanophenyl)-1H-tetrazole-5-thiol (SI-5c)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 1 started with 4-isothiocyanatobenzonitrile (1.00 g, 6.242 mmol, 1.0 equiv). The product was purified by silica pad filtration (EtOAc). The title compound was obtained in 345 mg (27%) as a beige solid. R = 0.23 (EtOAc 10: EtOH 1). H NMR (400 MHz; DMSO-d6): δ 8.24 (2H, m), 8.11 (2H, m). C{1H} NMR (100 MHz, DMSO-d6): δ 163.9, 137.7, 133.5, 124.4, 118.0, 111.9. HRMS-ESI (m/z): [M – H] calculated for C8H4N5S, 202.0187; found 202.0190. IR (νmax, film): 3076, 2937, 2239, 1607, 1476, 1352, 1272, 1045, 842, 578 cm–1. MP = 168–169 °C (EtOAc).

1-(4-Fluorophenyl)-1H-tetrazole-5-thiol (SI-5d)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 1 started with 1-fluoro-4-isothiocyanatobenzene (2.00 g, 13.056 mmol, 1.0 equiv). The product was purified by silica pad filtration (EtOAc). The title compound was obtained in 728 mg (28%) as a beige solid. R = 0.48 (EtOAc 10: EtOH 1). H NMR (400 MHz; DMSO-d6): δ 7.91 (2H, m), 7.46 (2H, m). C{1H} NMR (100 MHz, DMSO-d6): δ 164.1, 162.1 (d, J = 247.6 Hz), 130.3 (d, J = 3.1 Hz), 127.2 (d, J = 9.2 Hz), 116.3 (d, J = 23.3 Hz). HRMS-ESI (m/z): [M – H] calculated for C7H4N4FS, 195.0141; found 195.0149. IR (νmax, film): 3062, 2913, 2764, 1505, 1358, 1234, 1049, 834, 787, 570 cm–1. MP = 150–151 °C (EtOAc).

1-(2,6-Dimethoxyphenyl)-1H-tetrazole-5-thiol (SI-5e)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 1 started with 2-isothiocyanato-1,3-dimethoxybenzene (1.81 g, 9.270 mmol, 1.0 equiv). The product was purified by silica pad filtration (EtOAc). The title compound was obtained in 1.84 g (84%) as a beige solid. R = 0.32 (ethylacetate). H NMR (400 MHz; CDCl3): δ 10.90 (1H, br.s), 7.48 (1H, t, J = 8.5 Hz), 6.71 (2H, d, J = 8.5 Hz), 3.83 (6H, s). C{1H} NMR (100 MHz, CDCl3): δ 165.9, 156.8, 133.0, 110.6, 104.6, 56.4. HRMS-ESI (m/z): [M + Na] calculated for C9H10N4O2SNa, 261.0422; found 261.0415. IR (νmax, film): 3436, 2942, 2738, 2534, 1602, 1262, 1113, 776 cm–1. MP = 153–154 °C (EtOAc).

1-(2,6-Diisopropylphenyl)-1H-tetrazole-5-thiol (SI-5g)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 1 started with 1,3-diisopropyl-2-isothiocyanatobenzene (9.50 g, 39.845 mmol, 1.0 equiv). The title compound was obtained in 9.50 g (90%) as a beige solid. H NMR (400 MHz; CDCl3): δ 15.09 (1H, br.s), 7.58 (1H, t, J = 7.8 Hz), 7.37 (2H, d, J = 7.8 Hz), 2.40 (2H, hept, J = 6.9 Hz), 1.29 (6H, d, J = 6.9 Hz), 1.16 (6H, d, J = 6.9 Hz). C{1H} NMR (100 MHz, CDCl3): δ 166.0, 147.1, 132.1, 128.7, 124.6, 29.1, 24.4, 23.4. HRMS-ESI (m/z): [M + H] calculated for C13H19N4S, 263.1330; found 263.1336. IR (νmax, film): 3040, 2967, 2928, 2761, 2576, 1500, 1353, 1052, 802, 757 cm–1. MP = 135–136 °C (DCM).

General Procedure for the Preparation of Julia–Kocienski Reagents 11—Step 2

A suspension containing SI-5 (28.056 mmol, 1.0 equiv) and KOH (1.70 g, 30.862 mmol, 1.1 equiv) in ab. ethanol (50 mL) was stirred at room temperature for 15 min (until all solids dissolved). Then, ethyl iodide (2.5 mL, 30.862 mmol, 1.1 equiv) was added and stirring was continued for 4 h, during which a precipitate formed. Next, the suspension was evaporated, water (50 mL) was added, and the mixture was extracted with DCM (2 × 40 mL) and dried (Na2SO4). Volatiles were evaporated, and the residue was purified on silica gel (PE/DCM). The product-containing fractions were combined and evaporated in vacuo, furnishing the title compound.

5-(Ethylthio)-1-(4-methoxyphenyl)-1H-tetrazole (SI-6b)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 2 started with SI-5b (9.56 g, 57.913 mmol, 1.0 equiv). The title compound was purified by crystallization from EtOAc. The title compound was obtained in 6.39 g (46% in two steps) as a beige solid. R = 0.41 (PE 3: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.45 (2H, m), 7.03 (2H, m), 3.87 (3H, s), 3.38 (2H, q, J = 7.4 Hz), 1.48 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 160.9, 154.5, 126.5, 125.7, 115.0, 55.8, 27.8, 14.7. HRMS-ESI (m/z): [M + H] calculated for C10H13N4OS, 237.0810; found 237.0820. IR (νmax, film): 3467, 2971, 2845, 1607, 1515, 1453, 1251, 1170, 1089, 1021, 830, 625, 555 cm–1. MP = 92–93 °C (EtOAc).

5-(Ethylthio)-1-(4-cyanophenyl)-1H-tetrazole (SI-6c)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 2 started with SI-5c (345 mg, 1.697 mmol, 1.0 equiv). The title compound was precipitated from the reaction mixture and collected by filtration and washing of the filter cake with EtOH (2 mL). The title compound was obtained in 343 mg (87%) as a beige solid. R = 0.45 (PE 1: EtOAc 1). H NMR (400 MHz; DMSO-d6): δ 8.17 (2H, m), 7.92 (2H, m), 3.36 (2H, q, J = 7.3 Hz), 1.39 (3H, t, J = 7.3 Hz). C{1H} NMR (100 MHz, DMSO-d6): δ 154.6, 136.6, 134.2, 125.3, 117.8, 113.1, 27.6, 14.6. HRMS-ESI (m/z): [M – H] calculated for C10H10N5S, 232.0657; found 232.0666. IR (νmax, film): 3100, 2969, 2232, 1922, 1602, 1506, 1384, 1244, 1082, 839, 565 cm–1. MP >250 °C (dec; EtOH).

5-(Ethylthio)-1-(4-fluorophenyl)-1H-tetrazole (SI-6d)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 2 started with SI-5d (2.00 g, 13.056 mmol, 1.0 equiv). The title compound was purified on silica gel with PE/EtOAc 6:1 as an eluent. The title compound was obtained in 723 mg (87%) as a beige solid. R = 0.45 (PE 1: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.56 (2H, m), 7.26 (2H, m), 3.41 (2H, q, J = 7.4 Hz), 1.50 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 163.3 (d, J = 251.8 Hz), 154.6, 129.9 (d, J = 3.4 Hz), 126.2 (d, J = 8.8 Hz), 117.1 (d, J = 23.7 Hz), 27.9, 14.7. HRMS-ESI (m/z): [M + H] calculated for C9H10N4SF, 225.0610; found 225.0618. IR (νmax, film): 3080, 2975, 2933, 1514, 1387, 1236, 1083, 840, 623, 552 cm–1. MP = 58–59 °C (PE/EtOAc.)

1-(2,6-Dimethoxyphenyl)-5-(ethylthio)-1H-tetrazole (SI-6e)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 2 started from SI-5e (1.86 g, 7.806 mmol, 1.0 equiv). The title compound was purified on silica gel with PE/EtOAc 1:1 as an eluent. The title compound was obtained in 1.49 g (71%) as a white solid. R = 0.50 (PE 1: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.45 (1H, t, J = 8.6 Hz), 6.67 (2H, d, J = 8.6 Hz), 3.77 (6H, s), 3.30 (2H, q, J = 7.4 Hz), 1.42 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 156.8, 156.3, 132.8, 110.6, 104.4, 56.4, 27.5, 14.8. HRMS-ESI (m/z): [M + H] calculated for C11H15N4O2S, 267.0916; found 267.0916. IR (νmax, film): 2977, 2845, 1601, 1486, 1399, 1297, 1262, 1110, 775, 731, 650 cm–1. MP = 132–133 °C (PE/EtOAc).

1-(2,6-Dimethylphenyl)-5-(ethylthio)-1H-tetrazole (SI-6f)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. The procedure started with step 1 (2,6-dimethylphenyl isothiocyanate (6.24 g, 35.168 mmol, 1.0 equiv)) and step 2 (SI-5f). The title compound was collected by filtration and used in the next step as it was. The title compound was obtained in 8.10 g (90% in two steps) as a white solid. H NMR (400 MHz; CDCl3): δ 7.35 (1H, m), 7.19 (2H, m), 3.36 (2H, q, J = 7.3 Hz), 1.96 (6H, s), 1.46 (3H, t, J = 7.3 Hz). C{1H} NMR (100 MHz, CDCl3): δ 155.8, 136.1, 131.4, 131.2, 128.9, 27.2, 17.5, 14.8. HRMS-ESI (m/z): [M + H] calculated for C11H15N4S, 235.1017; found 235.1017. IR (νmax, film): 2975, 2931, 2871, 1476, 1387, 1265, 1234, 1092, 976, 790 cm–1. MP > 180 °C (dec; EtOH).

1-(2,6-Diisopropylphenyl)-5-(ethylthio)-1H-tetrazole (SI-6g)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 2 started with SI-5g (5.00 g, 19.056 mmol, 1.0 equiv). The title compound was purified on silica gel with PE/DCM 3:1 as an eluent. The title compound was obtained in 3.24 g (58%) as a white solid. R = 0.21 (PE 3: DCM 1). H NMR (400 MHz; CDCl3): δ 7.53 (1H, t, J = 7.9 Hz), 7.31 (2H, d, J = 7.9 Hz), 3.37 (2H, q, J = 7.3 Hz), 2.13 (2H, hept, J = 6.9 Hz), 1.46 (3H, t, J = 7.3 Hz), 1.18 (6H, d, J = 6.9 Hz), 1.10 (6H, d, J = 6.9 Hz). C{1H} NMR (100 MHz, CDCl3): δ 156.9, 146.7, 131.9, 128.5, 124.5, 28.7, 27.4, 24.5, 23.2, 14.8. HRMS-ESI (m/z): [M + H] calculated for C15H23N4S, 291.1643; found 291.1651. IR (νmax, film): 3459, 2967, 2931, 2872, 1465, 1390, 1266, 1086, 759 cm–1. MP = 71–72 °C (PE/DCM).

General Procedure for the Preparation of Julia–Kocienski Reagents 11—Step 3

To a solution of SI-6 (11.018 mmol, 1.0 equiv) in DCM (120 mL), NaHCO3 (4.62 g, 55.091 mmol, 5.0 equiv) and 70% mCPBA (6.17 g, 27.545 mmol, 2.5 equiv) were added subsequently and stirring was continued at rt for 16 h. After reaction completion, it was quenched with sat. Na2S2O3 (30 mL), then sat. NaHCO3 (30 mL) was added, and the mixture was extracted with DCM (2 × 100 mL). Combined organic extracts were washed with sat. NaHCO3 (200 mL) and brine (100 mL) and dried (Na2SO4). Volatiles were evaporated, and the residue was purified on silica gel or by crystallization.

5-(Ethylsulfonyl)-1-(4-methoxyphenyl)-1H-tetrazole (11b)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 3 started with SI-6b (4.10 g, 17.315 mmol, 1.0 equiv). The title compound was purified by crystallization from Et2O. The title compound was obtained in 3.66 g (78%) as a white solid. R = 0.48 (PE 1: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.59 (2H, m), 7.06 (2H, m), 3.89 (3H, s), 3.75 (2H, q, J = 7.4 Hz), 1.54 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 161.8, 153.2, 126.7, 125.8, 114.9, 55.8, 50.9, 7.1. HRMS-ESI (m/z): [M + Na] calculated for C10H12N4O3SNa, 291.0528; found 291.0540. IR (νmax, film): 3458, 3083, 2942, 1607, 1515, 1339, 1260, 1151, 1023, 836, 731, 612, 544 cm–1. MP = 58–59 °C (Et2O).

5-(Ethylsulfonyl)-1-(4-cyanophenyl)-1H-tetrazole (11c)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 3 started SI-6c (340 mg, 1.470 mmol, 1.0 equiv). The title compound was purified on silica gel with PE/EtOAc 1:1 as an eluent. The title compound was obtained in 140 mg (36%) as a white solid. R = 0.35 (PE 3: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.92 (4H, br.s), 3.82 (2H, q, J = 7.4 Hz), 1.57 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 153.3, 136.3, 133.8, 125.9, 117.2, 115.7, 51.1, 7.1. HRMS-ESI (m/z): [M – H] calculated for C10H8N5O2S, 262.0399; found 262.0407. IR (νmax, film): 3649, 3107, 3022, 2946, 2235, 1766, 1609, 1505, 1335, 1152, 1052, 845, 731, 545 cm–1.

5-(Ethylsulfonyl)-1-(4-fluorophenyl)-1H-tetrazole (11d)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 3 started with SI-6d (714 mg, 3.183 mmol, 1.0 equiv). The title compound was purified on silica gel with PE/EtOAc 3:1 as an eluent. The title compound was obtained in 625 mg (76%) as a white solid. R = 0.30 (PE 3: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.70 (2H, m), 7.29 (2H, m), 3.78 (2H, q, J = 7.4 Hz), 1.55 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 164.2 (d, J = 253.3 Hz), 153.3, 129.1 (d, J = 3.4 Hz), 127.4 (d, J = 9.2 Hz), 117.1 (d, J = 23.7 Hz), 51.0, 7.1. HRMS-ESI (m/z): [M + H] calculated for C9H10N4O2FS, 257.0508; found 257.0502. IR (νmax, film): 3086, 2988, 2946, 1514, 1341, 1234, 1151, 842, 730, 620, 543, 509 cm–1. MP = 44–45 °C (PE/EtOAc).

1-(2,6-Dimethoxyphenyl)-5-(ethylsulfonyl)-1H-tetrazole (11e)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 3 started with SI-6e (1.49 g, 5.594 mmol, 1.0 equiv). The title compound was purified by crystallization from PE/EtOAc. The title compound was obtained in 920 mg (55%) as a white solid. R = 0.38 (PE 1: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.50 (1H, t, J = 8.6 Hz), 6.70 (2H, d, J = 8.6 Hz), 3.79 (6H, s), 3.52 (2H, q, J = 7.4 Hz), 1.41 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 155.9, 154.1, 133.4, 111.0, 104.4, 56.4, 50.9, 6.7. HRMS-ESI (m/z): [M + H] calculated for C11H15N4O4S, 299.0814; found 299.0811. IR (νmax, film): 2950, 2846, 1605, 1487, 1345, 1266, 1113, 1014, 782, 732, 618, 500 cm–1. MP = 124–125 °C (PE/EtOAc).

1-(2,6-Diisopropylphenyl)-5-(ethylsulfonyl)-1H-tetrazole (11g)

Prepared according to the general procedure for the preparation of Julia–Kocienski reagents 11. Step 3 started with SI-6g (4.37 g, 15.046 mmol, 1.0 equiv). The title compound was purified on silica gel with PE/DCM 1:2 as an eluent. The title compound was obtained in 3.38 g (80%) as a white solid. R = 0.35 (PE 10: EtOAc 1). H NMR (400 MHz; CDCl3): δ 7.57 (1H, t, J = 7.9 Hz), 7.33 (2H, d, J = 7.9 Hz), 3.71 (2H, q, J = 7.5 Hz), 2.02 (2H, hept, J = 6.8 Hz), 1.52 (3H, t, J = 7.5 Hz), 1.24 (6H, d, J = 6.8 Hz), 1.08 (6H, d, J = 6.8 Hz). C{1H} NMR (100 MHz, CDCl3): δ 154.3, 146.2, 132.4, 128.6, 124.3, 50.6, 29.2, 25.3, 22.2, 6.9. HRMS-ESI (m/z): [M + H] calculated for C15H23N4O2S, 323.1542; found 323.1542. IR (νmax, film): 2974, 2929, 2871, 1457, 1339, 1150, 1059, 808, 760, 737, 548, 501 cm–1. MP = 93–94 °C (PE/DCM).

Optimized Synthesis of 11g

A suspension of 2,6-diisopropylphenyl isothiocyanate (10.00 g, 41.942 mmol, 1.0 equiv) and NaN3 (5.45 g, 83.885 mmol, 2.0 equiv) in abs. EtOH (100 mL) was heated under reflux for 3 h. Then, the reaction mixture was cooled to room temperature, iodoethane (5.0 mL, 62.913 mmol, 1.5 equiv) was added, and the resulting mixture was stirred at room temperature for 3 h. The reaction was quenched by the addition of H2O (100 mL) and extracted once with DCM (100 mL). The organic extract was dried over Na2SO4 and filtered, and the solvents were removed in vacuo. The crude product (13.14 g) was dissolved in EtOH (150 mL) and cooled (ice bath), and (NH4)6Mo7O24 × 4H2O (5.23 g, 4.194 mmol, 0.1 equiv) was added followed by 35% aq H2O2 (36 mL, 419.432 mmol, 10.0 equiv). The resulting mixture was stirred at room temperature in a sealed tube for 24 h. Then, the suspension was poured into H2O (150 mL) and the precipitate was collected by filtration. The filter cake was washed with H2O (100 mL) and dried under vacuum (at 50 °C over P2O5 for 2 days) to obtain 12.28 g (90% in three steps) of 11f as a white solid.

1-(2,6-Dimethylphenyl)-5-(ethylsulfonyl)-1H-tetrazole (11f)

Prepared according to the optimized procedure for the preparation of Julia–Kocienski reagents 11. The procedure started with 2,6-dimethylphenyl isothiocyanate (6.24 g, 35.168 mmol, 1.0 equiv). The title compound was obtained in 7.05 g (75%) as a white solid. H NMR (400 MHz; CDCl3): δ 7.41 (1H, m), 7.23 (2H, m), 3.73 (2H, q, J = 7.5 Hz), 2.00 (6H, s), 1.54 (3H, t, J = 7.4 Hz). C{1H} NMR (100 MHz, CDCl3): δ 154.0, 135.9, 131.8, 131.6, 128.9, 50.6, 17.4, 7.1. HRMS-ESI (m/z): [M + H] calculated for C11H15N4O2S, 267.0916; found 267.0925. IR (νmax, film): 2984, 2928, 1477, 1456, 1400, 1342, 1336, 1151, 777, 622, 542, 506 cm–1. MP > 180 °C (dec; EtOH, H2O).

General Procedure for Olefination of 10

To a solution of sulfone (0.374 mmol, 3.0 equiv) in THF (2 mL; freshly distilled over Na/Ph2CO) at −78 °C was added 1 M KHMDS (made prior to use: 78.5 mg, 0.374 mmol, 3.0 equiv dissolved in 0.37 mL of THF), and the mixture was stirred at the same temperature for 15 min. Next, a solution of 10 (0.124 mmol, 1.0 equiv) in THF (1.5 mL) was added, and the resulting mixture was stirred for 15 min at −78 °C before being quenched with sat. NH4Cl (4 mL). Then, brine (4 mL) was added, the organic layer was separated, and the aqueous phase was extracted with EtOAc (2 × 10 mL). The combined organic extracts were dried (Na2SO4), and volatiles were evaporated in vacuo. At this point, the qNMR spectrum was measured. The analytically pure sample was obtained by purification of the crude product by flash column chromatography.

(S,E)-2-Ethylidene-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (12a)

Prepared according to the general procedure for the olefination of 10 starting from trione 10a. An analytically pure sample was obtained by purification of the crude reaction mixture on silica gel with PE/EtOAc 2:1 as an eluent. The title compound was obtained as colorless oil. R = 0.45 (PE 1: EA 1). For the isomer, H NMR (400 MHz; CDCl3): δ 7.89 (1H, dd, J = 7.8, 1.7 Hz), 7, 68 (1H, m), 7.52 (1H, m), 7.33 (1H, m), 5.54 (1H, m), 5.51 (1H, d, J = 9.9 Hz), 4.71 (1H, d, J = 9.9 Hz), 4.37–4.13 (3H, m), 3.75 (1H, m), 3.65 (1H, m), 3.47 (1H, m), 2.62 (1H, m), 1.74 (3H, m), 0.98 (2H, m), 0.02 (9H, s). For the isomer, H NMR (400 MHz; CDCl3): δ 7.90 (1H, dd, J = 7.8, 1.7 Hz), 7,68 (1H, m), 7.52 (1H, m), 7.33 (1H, m), 5.54 (1H, m), 5.50 (1H, d, J = 9.9 Hz), 4.72 (1H, d, J = 9.9 Hz), 4.37–4.13 (3H, m), 3.75 (1H, m), 3.65 (1H, m), 3.37 (1H, m), 2.77 (1H, m), 1.81 (1H, m), 0.98 (2H, m), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.10 and 170.04 (isomers), 165.58 and 165.37 (isomers), 139.97, 133.15 and 133.11 (isomers), 132.47, 130.03, 129.63 and 129.58 (isomers), 126.47, 122.70, 118.87 and 118.55 (isomers), 78.18 and 78.12 (isomers), 67.18 and 67.10 (isomers), 57.63 and 57.14 (isomers), 51.14 and 48.14 (isomers), 32.18 and 28.23 (isomers), 18.43, 15.02 and 14.64 (isomers), −1.25. HRMS-ESI (m/z): [M + Na] calculated for C20H28N2O3SiNa, 395.1767; found 395.1765. IR (νmax, film): 3272, 2952, 1644, 1461, 1420, 1377, 1248, 1071, 836, 762 cm–1. [α] = 252° (c = 0.1, CHCl3).

(S,E)-7-Chloro-2-ethylidene-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (12b)

Prepared according to the general procedure for the olefination of 10 starting from trione 10b. An analytically pure sample was obtained by purification of the crude reaction mixture on silica gel with DCM/MeOH 50:1 as an eluent. The title compound was obtained as colorless oil. R = 0.45 (DCM 50: MeOH 1). H NMR (400 MHz; CDCl3): δ 7.88 (1H, d, J = 2.6 Hz), 7.66 (1H, d, J = 8.7 Hz), 7.47 (1H, dd, J = 8.7, 2.6 Hz), 5.54 (1H, m), 5.51 (1H, d, J = 9.9 Hz), 4.66 (1H, d, J = 9.9 Hz), 4.36–4.23 (2H, m), 4.21–4.11 (1H, m), 3.81–3.61 (2H, m), 3.52–3.33 (1H, m), 2.85–2.57 (1H, m), 1.78–1.63 (3H, m), 0.98 (2H, m), 0.02 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.7, 164.1, 138.5, 132.8, 132.5, 132.3, 130.9, 129.8, 124.2, 118.8, 78.1, 67.3, 57.6, 51.3, 28.2, 18.4, 14.7, −1.2. HRMS-ESI (m/z): [M – H] calculated for C20H27ClN2O3SiNa, 405.1401; found 405.1385. IR (νmax, film): 2924, 2857, 1694, 1649, 1443, 1365, 1248, 1073, 837 cm–1. [α] = 214° (c = 0.1, CHCl3).

(S,E)-2-Ethylidene-8-(trifluoromethyl)-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (12c)

Prepared according to the general procedure for the olefination of 10 starting from trione 10c. An analytically pure sample was obtained by purification of the crude reaction mixture on silica gel with DCM/MeOH 50:1 as an eluent. The title compound was obtained as colorless oil. H NMR (400 MHz; CDCl3): δ 8.05–8.00 (2H, m), 7.59 (1H, m), 5.56 (2H, m), 4.70 (1H, d, J = 10.0 Hz), 4.34 (1H, m), 4.28 (1H, dd, J = 9.1, 2.3 Hz), 4.18 (1H, m), 3.79 (1H, m), 3.69 (1H, m), 3.53–3.35 (1H, m), 2.84–2.60 (1H, m), 1.78–1.64 (3H, m), 0.99 (2H, m), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 169.7, 164.2, 140.4, 134.4 (q, J = 32.5 Hz), 132.6, 132.4, 131.1, 123.2 (q, J = 273.8 Hz), 123.0 (q, J = 3.7 Hz), 120.0 (q, J = 3.7 Hz), 119.0, 78.1, 67.5, 57.6, 51.3, 28.3, 18.3, 14.7, −1.3. HRMS-ESI (m/z): [M – H] calculated for C21H27F3N2O3Si, 439.1665; found 439.1669. IR (νmax, film): 2924, 2855, 1698, 1655, 1449, 1180, 1134, 1085, 835, 627 cm–1. [α] = 60° (c = 0.1, CHCl3).

(S,E)-2-Ethylidene-9-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (12d)

Prepared according to the general procedure for the olefination of 10 starting from trione 10d. An analytically pure sample was obtained by purification of the crude reaction mixture on silica gel with PE/EtOAc 1:1 as an eluent. The title compound was obtained as colorless oil. R = 0.26 (PE 1: EA 1). For the isomer, H NMR (600MHz; CDCl3): δ 7.47 (1H, m), 7.34 (1H, m), 7.07 (1H, m), 5.72 (1H, m), 5.56–5.47 (1H, m), 5.01 (1H, m), 4.33–4.10 (3H, m), 3.89 (3H, m), 3.44–3.27 (3H, m), 2.57 (1H, m), 1.72 (3H, m), 0.81–0.65 (2H, m), 0.08 (9H, s). For the isomer, H NMR (600MHz; CDCl3): δ 7.47 (1H, m), 7.34 (1H, m), 7.07 (1H, m), 5.72 (1H, m), 5.56–5.47 (1H, m), 5.01 (1H, m), 4.33–4.10 (3H, m), 3.89 (3H, m), 3.44–3.27 (3H, m), 2.71 (1H, m), 1.64 (3H, m), 0.81–0.65 (2H, m), 0.08 (9H, s). C{1H} NMR (150 MHz, CDCl3): δ 170.85 and 170.78 (isomers), 165.26 and 165.02 (isomers), 152.80, 134.00 and 133.96 (isomers), 133.42 and 133.34 (isomers), 128.13, 126.73, 121.36, 118.68 and 118.31 (isomers), 114.34, 75.10 and 74.97 (isomers), 66.26, 58.02 and 57.54 (isomers), 55.99, 50.83 and 47.95 (isomers), 31.79 and 27.94 (isomers), 17.96 and 17.92 (isomers), 15.00 and 14.65 (isomers), −1.35. HRMS-ESI (m/z): [M + Na] calculated for C21H30N2O4SiNa, 425.1873; found 425.1876. IR (νmax, film): 2951, 1689, 1651, 1410, 1247, 1066, 836, 755 cm–1. [α] = 167° (c = 0.1, CHCl3).

(S,E)-2-Ethylidene-7,8-dimethoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (12e)

Prepared according to the general procedure for the olefination of 10 starting from trione 10e. An analytically pure sample was obtained by purification of the crude reaction mixture on silica gel with PE/EtOAc 2:1 as an eluent. The title compound was obtained as colorless oil. For the isomer, H NMR (400 MHz; CDCl3): δ 7.34 (1H, d, J = 2.0 Hz), 7.24 (1H, d, J = 2.0 Hz), 5.52 (1H, d, J = 9.9 Hz), 5.52 (1H, m), 4.63 (1H, d, J = 9.9 Hz), 4.37–4.08 (3H, m), 3.94 (3H, s), 3.92 (3H, s), 3.79 (1H, m), 3.68 (1H, m), 3.47 (1H, m), 2.62 (1H, m), 1.74 (3H, m), 0.98 (2H, m), 0.03 (9H, s). For the isomer, H NMR (400 MHz; CDCl3): δ 7.34 (1H, d, J = 2.0 Hz), 7.24 (1H, d, J = 2.0 Hz), 5.52 (1H, d, J = 9.9 Hz), 5.52 (1H, m), 4.64 (1H, d, J = 9.9 Hz), 4.37–4.08 (3H, m), 3.94 (3H, s), 3.92 (3H, s), 3.79 (1H, m), 3.68 (1H, m), 3.36 (1H, m), 2.76 (1H, m), 1.65 (3H, m), 0.98 (2H, m), 0.03 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.1, 165.3, 152.0, 147.2, 134.3, 133.3, 121.9, 118.5, 111.1, 105.6, 78.3, 67.2, 57.8, 56.3, 56.3, 51.2, 28.2, 18.5, 14.6, −1.2. HRMS-ESI (m/z): [M + Na] calculated for C22H32N2O5SiNa, 455.1978; found 455.1977. IR (νmax, film): 3431, 2955, 2925, 2854, 1700, 1652, 1520, 1456, 1248, 1075, 837 cm–1. [α] = 287° (c = 0.1, CHCl3).

(S,E)-8-(Benzyloxy)-2-ethylidene-7-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepine-5,11(10H)-dione (12f)

Prepared according to the general procedure for the olefination of 10 starting from trione 10f. An analytically pure sample was obtained by purification of the crude reaction mixture on silica gel with PE/EtOAc 1:1 as an eluent. The title compound was obtained as colorless oil. R = 0.30 (PE 1: EA 1). H NMR (400 MHz; CDCl3): δ 7.46–7.41 (2H, m), 7.39–7.28 (4H, m), 7.25 (1H, s), 5.52 (1H, m), 5.43 (1H, d, J = 9.8 Hz), 5.20 (2H, s), 4.47 (1H, d, J = 9.8 Hz), 4.32 (1H, m), 4.27 (1H, dd, J = 9.2, 2.4 Hz), 4.12 (1H, m), 3.94 (3H, s), 3.70 (1H, td, J = 9.5, 7.2 Hz), 3.60 (1H, td, J = 9.5, 7.2 Hz), 3.45 (1H, br.d, J = 16.2 Hz), 2.60 (1H, m), 1.73 (3H, m), 0.97 (2H, m), 0.04 (9H, s). C{1H} NMR (100 MHz, CDCl3): δ 170.0, 165.2, 150.9, 147.7, 136.1, 134.0, 133.3, 128.8, 128.3, 127.6, 122.0, 118.4, 111.4, 107.8, 78.2, 71.0, 67.1, 57.7, 56.4, 51.2, 28.2, 18.5, 14.6, −1.2. HRMS-ESI (m/z): [M + H] calculated for C28H37N2O5Si, 509.2472; found 509.2448. IR (νmax, film): 2951, 1689, 1639, 1516, 1436, 1362, 1248, 1069, 836, 751, 696 cm–1. [α] = 272° (c = 0.1, CHCl3).

Oxo-prothracarcin (4)

To a stirred solution of 12a (22 mg, 0.059 mmol, 1.0 equiv) in THF (1 mL) was added concn HCl (246 μL, 2.95 mmol, 50.0 equiv), and the resulting mixture was heated for 1 h at 60 °C. The volatiles were evaporated in vacuo, and the oily residue was purified on silica gel (DCM/MeOH 20:1) to furnish 8 mg (55%) of oxo-prothracarcin (4) as colorless wax. R = 0.35 (DCM 20: MeOH 1). For the -isomer, H NMR (400 MHz; CD3OD): δ 7.87 (1H, ddd, J = 7.9, 1.6, 0.3 Hz), 7.55 (1H, ddd, J = 8.2, 7.4, 1.7 Hz), 7.29 (1H, m), 7.14 (1H, m), 5.57 (1H, m), 4.37 (1H, dd, J = 9.2, 2.4 Hz), 4.31 (1H, m), 4.13 (1H, dq, J = 16.0, 1.8 Hz), 3.45 (1H, br.d, J = 16.2 Hz), 2.69 (1H, m), 1.75 (3H, m). For the -isomer, H NMR (400 MHz; CD3OD): δ 7.88 (1H, ddd, J = 7.9, 1.6, 0.3 Hz), 7.55 (1H, ddd, J = 8.2, 7.4, 1.7 Hz), 7.29 (1H, m), 7.14 (1H, m), 5.57 (1H, m), 4.37–4.19 (3H, m), 3.35–3.28 (1H, m (partially overlapping with CD3OD)), 2.83 (1H, m), 1.68 (3H, m). C{1H} NMR (100 MHz, CD3OD): δ 172.2, 167.8, 137.8, 134.5 and 134.4 (isomers), 133.9, 131.4 and 127.4 (isomers), 125.8, 122.6, 119.4 and 119.1 (isomers), 58.4 and 57.8 (isomers), 52.5, 32.4 and 28.2 (isomers), 14.8 and 14.5 (isomers). HRMS-ESI (m/z): [M + H] calculated for C14H15N2O2, 243.1134; found 243.1140. IR (νmax, film): 3218, 2920, 2854, 1694, 1622, 1446, 1257, 760 cm–1. [α] = 481.0° (c = 0.1, MeOH).

Oxo-tomaymycin (5)

To a solution of 12f (211 mg, 0.414 mmol, 1.0 equiv) in DCM (4 mL), anisole (0.77 mL, 7.051 mmol, 17 equiv) and methanesulfonic acid (0.46 mL, 7.051 mmol, 17 equiv) were added sequentially at room temperature, and the mixture was stirred for 16 h. The volatiles were evaporated in vacuo, and the oily residue was purified on a reverse-phase column (eluent: MeCN/water 5:95% → 95:5%) to furnish 54 mg (45%) of oxo-tomaymycin (5) as a white powder. R = 0.41 (DCM 10: MeOH 1). For the -isomer, H NMR (400 MHz; CDCl3): δ 10.28–10.21 (1H, m), 9.94 (1H, br.s), 7.26–7.18 (1H, m), 6.60–6.54 (1H, m), 5.47 (1H, m), 4.36–4.08 (2H, m), 4.08–3.91 (1H, m), 3.78 (3H, s), 3.25 (1H, br.d, J = 16.2 Hz), 2.77–2.53 (1H, m), 1.66 (3H, m). For the -isomer, H NMR (400 MHz; CDCl3): δ 10.28–10.21 (1H, m), 9.94 (1H, br.s), 7.26–7.18 (1H, m), 6.60–6.54 (1H, m), 5.52 (1H, m), 4.36–4.08 (2H, m), 4.08–3.91 (1H, m), 3.78 (3H, s), 3.15 (1H, br.d, J = 16.2 Hz), 2.77–2.53 (1H, m), 1.60 (3H, m). C{1H} NMR (100 MHz, CD3OD): δ 172.0, 167.8, 152.4, 146.6, 134.7, 132.6, 118.9, 118.7, 112.9, 108.9, 58.5, 56.6, 52.5, 28.2 and 22.8 (isomers), 14.5 and 12.1 (isomers). HRMS-ESI (m/z): [M + H] calculated for C15H17N2O4, 289.1188; found 289.1202. IR (νmax, film): 3529, 3403, 2919, 2610, 2417, 1677, 1611, 1482, 1268, 878, 759 cm–1. [α] = 391° (c = 0.1, MeOH).

Boseongazepine B (6)

To a stirred solution of 12d (100 mg, 0.248 mmol, 1.0 equiv) in THF (3 mL) was added concn HCl (300 μL, 3.600 mmol, 15.0 equiv), and the resulting mixture was heated for 16 h at 60 °C. The volatiles were evaporated in vacuo, and the oily residue was purified on silica gel (DCM/MeOH 40: 1) to furnish 42 mg (62%) of boseongazepine B (5) as colorless wax. R = 0.45 (DCM 40: MeOH 1). For the -isomer, H NMR (400 MHz; CD3OD): δ 7.47–7.39 (1H, m), 7.31–7.19 (2H, m), 5.57 (1H, m), 4.39–4.22 (2H, m), 4.12 (1H, m), 3.94 (3H, s), 3.44 (1H, br.d, J = 16.2 Hz), 2.69 (1H, m), 1.74 (3H, m). For the -isomer, H NMR (400 MHz; CD3OD): δ 7.47–7.39 (1H, m), 7.31–7.19 (2H, m), 5.57 (1H, m), 4.39–4.22 (2H, m), 4.12 (1H, m), 3.94 (3H, s), 3.44 (1H, br.d, J = 16.2 Hz), 2.82 (1H, m), 1.67 (3H, m). C{1H} NMR (100 MHz, CD3OD): δ 171.9, 167.5, 151.3, 134.5 and 134.4 (isomers), 128.6, 127.1, 126.3, 122.4, 119.4 and 119.1 (isomers), 114.8, 58.5 and 58.0 (isomers), 56.8, 52.5, 32.3 and 28.2 (isomers), 14.8 and 14.5 (isomers). HRMS-ESI (m/z): [M + H] calculated for C15H17N2O3, 273.1239; found 273.1252. IR (νmax, film): 3257, 2982, 2920, 2860, 1693, 1413, 1261, 1068, 750 cm–1. [α] = 571° (c = 0.1, MeOH).