Asymmetric Redox-Annulation of Cyclic Amines.

Cyclic amines such as 1,2,3,4-tetrahydroisoquinoline undergo regiodivergent annulation reactions with 4-nitrobutyraldehydes. These redox-neutral transformations enable the asymmetric synthesis of highly substituted polycyclic ring systems in just two steps from commercial materials. The utility of this process is illustrated in a rapid synthesis of (-)-protoemetinol. Computational studies provide mechanistic insights and implicate the elimination of acetic acid from an ammonium nitronate intermediate as the rate-determining step.

Introduction

Tryptoline (tetrahydro-β-carboline) and 1,2,3,4-tetrahydroisoquinoline (THIQ) are substructures of numerous bioactive natural products that contain additional fused rings (Scheme ).[1] The desire to build such highly substituted polycyclic compounds with complete stereocontrol has inspired the development of numerous synthetic methods.[2] Here, we report a redox-neutral annulation strategy that enables the asymmetric synthesis of relevant core structures from simple THIQ or tryptoline and readily available, highly enantioenriched 4-nitrobutyraldehydes.

Scheme 1

Selected Natural Products with THIQ and Tryptoline Substructures

As part of our ongoing efforts to develop practical methods for the C–H functionalization of amines,[3,4] we recently reported the first examples of what may be termed a redox-annulation of amines (Scheme ).[3b] Conceptually, an amine such as THIQ engages an aldehyde with a pendent carbon nucleophile to form product 2 via reductive N-alkylation/oxidative C–C bond formation in an overall redox-neutral process.[5] Condensation of the two components initially forms an azomethine ylide intermediate 1 that, following proton transfer and ring closure, provides product 2.[6−9] For instance, THIQ and indole aldehyde 3 form annulation product 4 in 64% yield.[3b] While this is a clear demonstration of the utility of this approach for the facile preparation of polycyclic ring systems, the method requires relatively high reaction temperatures. More serious limitations are the need for using nonenolizable aldehydes and electron-rich aromatic nucleophiles (e.g., indole, β-naphthol).

Scheme 2

Redox-Annulation

In order to be applicable to the synthesis of structures related to those shown in Scheme , the redox-annulation would have to proceed with enolizable aldehydes capable of installing a fully saturated ring bearing variable substituents. These considerations, coupled with our goal to perform amine redox-annulations in asymmetric fashion, led to the identification of 4-nitrobutyraldehydes 5 as ideal reaction partners. These precursors are easily prepared in a single step and nearly enantiopure form from aldehydes and nitroalkenes by means of well-established organocatalytic methods.[10] The corresponding annulation products 6 are equipped with substituents in relevant positions and, due to the presence of a nitro group, offer numerous opportunities for further product manipulation.[11]

Experimental Results and Discussion

We began our investigation into the feasibility of the proposed annulation process by employing 5a and THIQ as model substrates (Table ). The original annulation conditions developed for product 4 failed to provide any desired product (entry 1). Addition of acetic acid (1 equiv), an additive previously shown to be an excellent promoter for amine α-oxygenation[3h] and α-sulfenylation,[3j] did not provide any improvements (entry 2). Gratifyingly, the use of 5 equiv of acetic acid under otherwise identical conditions allowed for the isolation of the desired product as a 1.8:1 mixture of diastereomers 6a and 7a in 45% overall yield. The formation of 7a is readily rationalized by the intermediacy of enamines, causing epimerization of the stereogenic center in α-position of the aldehyde prior to the annulation step. Excess acetic acid apparently reduces the concentration of enamine intermediates, facilitating the redox-isomerization and minimizing undesired side reactions. Indeed, further increase of the amount of acetic acid to 10 equiv led to an increase in yield to 65% (entry 4). With 2-ethylhexanoic acid (2-EHA), the product yield was only 30% (entry 5). Remarkably, with benzoic acid, previously shown to be an excellent catalyst for amine α-functionalizations, no desired product was formed; only epimerization of the starting material was observed (entry 6). Addition of molecular sieves had a beneficial effect, and the amount of THIQ could be lowered to 2 equiv (entry 7). A reduction in temperature from 150 to 120 °C, while reducing the reaction time from 15 to 2 min, led to a further increase in yield to 71% (entry 8). A reaction performed under simple reflux conditions was completed in only 1 h and gave rise to nearly identical results (entry 9). Even at a temperature of only 60 °C, the reaction progressed in an efficient manner (entry 10). For the sake of convenience and to keep reaction times brief, subsequent experiments were performed under reflux in toluene.

Table 1

Evaluation of Reaction Conditionsa

entry	acid (equiv)	temp (°C)	time (min)	yield (%)	ratio 6a:7a
1		150 (μW)	15	complex	ND
2	AcOH (1)	150 (μW)	15	complex	ND
3	AcOH (5)	150 (μW)	15	45	1.8:1
4	AcOH (10)	150 (μW)	15	65	2:1
5	2-EHA (10)	150 (μW)	15	30	1:1
6	PhCO2H (10)	150 (μW)	15	NRb
7c	AcOH (10)	150 (μW)	15	65	1.8:1
8c	AcOH (10)	120 (μW)	2	71	1.8:1
9c	AcOH (10)	reflux	1 h	71	2:1d
10c	AcOH (10)	60	15 h	62	2:1

Reactions were performed with 5a (0.2 mmol) and THIQ (4 equiv). Product ratios were determined by 1H NMR analysis of the crude reaction mixture. Yields correspond to combined, isolated yields of both diastereomers. ND: not determined. NR: no reaction.

Partially epimerized starting material was recovered (dr = 1:1).

Performed with 5a (0.6 mmol) and 2 equiv of THIQ in the presence of 4 Å MS.

Both 6a and 7a were obtained with 95% ee.

The scope of the asymmetric redox-annulation of THIQ was explored with a range of 4-nitrobutyraldehydes (Scheme ). α,β-Disubstituted 4-nitrobutyraldehydes 5 with various substitution patterns readily underwent the title reaction, providing products 6/7 in moderate to good yields and with diastereoselectivities of up to 5:1. Notably, in all cases, separation of the two diastereomeric products was readily accomplished by standard column chromatography. 4-Nitrobutyraldehydes without α-substituents gave rise to products 6 with good to excellent levels of diastereoselectivity.[12] Importantly, the reaction of mono- and disubstituted 4-nitrobutyraldehydes was also applicable to substituted THIQs and tryptoline.

Scheme 3

Scope of the Asymmetric Redox-Annulation

Reactions were performed on a 0.6 mmol scale. For products 6a/7a–6j/7j, yields correspond to combined, isolated yields of both diastereomers. For products 6k–t, yields correspond to isolated yields of the major diastereomer.

During the development of the title reaction, we occasionally observed small amounts of the regioisomeric annulation products 8 and 9 (Scheme ). Following extensive experimentation, conditions were identified that provided 8 and 9 as the major products with regioselectivities of up to nearly 9:1.[13] Diastereoselectivities were similar to those observed in redox-annulations that involve the benzylic position, with β-monosubstituted 4-nitrobutyraldehydes providing products 8 in highly diastereoselective fashion. Key to accomplishing redox-annulations at the less reactive α-C–H bond is performing the reaction at higher temperature (reflux in xylenes) and to maintain a low concentration of 5. This was achieved by syringe pump addition of the corresponding 4-nitrobutyraldehyde. Best results were obtained in the absence of molecular sieves.[14]

Scheme 4

Divergent Regioselectivity in the Asymmetric Redox-Annulation

Reactions were performed on a 0.6 mmol scale.

Redox-annulations of THIQ were also performed with parent 4-nitrobutyraldehyde 10eqs and 2. Regioselective annulation was accomplished at either position through judicious choice of reaction conditions. Diastereomeric products 11 and 12 were obtained in a 2:1 ratio and 55% overall yield (eq ). This appears to correspond to the thermodynamic equilibrium ratio of these two products.[15] Notably, product 13 was obtained as a single diastereo- and regioisomer in 61% yield (eq ).

Products derived from the redox-annulation could be readily modified. For instance, reduction of 8k with Zn/HCl provided amine 15 in 83% yield (eq ). Removal of the nitro group in 6k via hydrogenolysis provided heterocycle 16 in 75% yield (eq . Importantly, the enantiomeric purity of the material was not affected by this transformation. Finally, compound 11 was alkylated with methyl vinyl ketone in the presence of DBU to yield product 17 as a single diastereomer in 69% yield (eq ).

The asymmetric redox-annulation was applied to a short synthesis of the natural product (−)-protoemetinol (Scheme ). Condensation of 6,7-dimethoxy-THIQ and 18 resulted in the formation of 19 and two of its diastereomers in 61% overall yield. The major diastereomer was converted to (−)-protoemetinol in a single operation that served to remove both the nitro and benzyl groups.

Scheme 5

Synthesis of (−)-Protoemetinol

Computational Results and Discussion

To shed light on the mechanism of the redox-annulations discussed above and to rationalize the high regioselectivities of eqs and 2, we carefully analyzed the reaction between THIQ and 4-nitrobutyraldehyde (10) by DFT calculations [M06-2X-D3/def2-QZVP/IEFPCM//M06-L-D3/6-31+G(d,p)/IEFPCM]. Although the uncatalyzed reaction of THIQ and 10 results in complex mixtures, knowledge of this pathway is important to understand any potential background reaction (Scheme ). Consequently, the uncatalyzed pathway was evaluated first. In the first step of this transformation, THIQ and 10 form the hemiaminal 20 in an almost thermoneutral reaction. Water can be eliminated from 20 in two different orientations yielding the azomethine ylides 21a and 21b in highly endergonic transformations (ΔG = +18.9 and +30.1 kcal mol–1). Due to the direct conjugation of the azomethine ylide with the benzene ring, ylide 21a is significantly more stable than its isomer 21b. We were unable to locate any transition states for this elimination, and all attempts starting from different transition state guesses resulted in a barrierless addition of water to the corresponding azomethine ylides. Therefore, it was concluded that this reaction occurs without a significant barrier which can be rationalized with the high reactivities of the formed azomethine ylides. In principle, the hemiaminal 20 could also form the corresponding enamine (not shown in Scheme ) through another elimination of water. This transformation is thermoneutral (ΔG = −0.1 kcal mol–1) and can account for the epimerization of α-substituted aldehydes (Table1). Next, an intramolecular proton transfer takes place between the nitroalkane moiety and the ylide. In both transition states TS01a and TS01b, the proton transfers occur through five-membered transition states and are very high in energy (ΔG⧧ = +42.9 and +47.1 kcal mol–1). In an alternative pathway, the zwitterions 22 could also be formed via a zwitterionic intermediate with an exocyclic double bond (not shown in Scheme ). As this isomer is formed in a highly endergonic step (ΔG = +25 kcal mol–1) and requires a highly unfavorable 1,3-proton shift, this pathway seems less likely. The zwitterions 22a and 22b subsequently undergo intramolecular cyclization reactions to either form the diastereomeric products 11 and 12 or the regioisomers 13 and 14. These reactions occur without a significant barrier, which can be explained by the high reactivities of nitronate anions and iminium cations.[16] Our calculations predict a small thermodynamic preference (ΔΔG = 0.9 kcal mol–1) for the cis-product 11 over the trans-product 12, which is in good agreement with the experimental 2:1 ratio. A much stronger preference (ΔΔG = 2.0 kcal mol–1) for the cis-isomer was calculated for 13 compared to 14 in line with the exclusive isolation of 13.

Scheme 6

Calculated Free Energies for the Uncatalyzed and Acetic-Acid-Catalyzed Annulation Reactions and Selected Transition-State Structures [kcal mol–1, M06-2X-D3/def2-QZVP/IEFPCM//M06-L-D3/6-31+G(d,p)/IEFPCM]

As the intramolecular proton transfers yielding the zwitterions 22 are very high in energy, we were wondering whether acetic acid could act as a proton shuttle to bypass TS1a and TS1b as seen in related oxygenation and sulfenylation reactions.[3h,3j] However, starting from many different transition-state guesses, we were unable to locate any transition states for such mechanisms. Instead, these structures relaxed to hydrogen-bonded adducts between acetic acid and different polar groups of the azomethine ylides. Furthermore, acetic acid could also facilitate the formation of iminium ions as intermediates in these transformations, but based on our calculations, iminium ions are very high in energy (ΔG⧧ > 47 kcal mol–1; see the Supporting Information for more details) and were thus ruled out. Instead, we considered a concerted elimination of acetic acid from acetylated hemiaminals (N,O-acetals) as an alternative mechanism (e.g., 23, 24, and 27), as previously suggested by Yu and co-workers in the formation of pyrroles from pyrroline and aldehydes.[17]

According to the calculated free energy profile in Scheme , the combination of THIQ, 10, and AcOH results in the formation of the N,O-acetal 23 in a slightly endergonic reaction. Subsequently, acetic acid is eliminated in a concerted yet highly asynchronous transition state (TS02, see the Supporting Information) yielding the azomethine ylide 21a. Next, acetic acid adds across the other terminus of the ylide (TS03), resulting in the formation of the more stable isomeric N,O-acetal 24. This intermediate can now react via two pathways to form either the product 11 (or 12) or the regioisomer 13. For the formation of 11, the next step involves an intramolecular deprotonation of an acidic proton in α-position of the nitro group. This reaction proceeds through a six-membered transition state (TS04) and yields the ammonium nitronate 25. This endergonic step is also reflected in a very late transition state with a short N–H bond (1.14 Å). Next, acetic acid is eliminated through TS05 (ΔG⧧ = 30.5 kcal mol–1), which is also the rate-determining step for the formation of 11. This reaction proceeds in a concerted yet highly asynchronous fashion in which the cleavage of the C–O bond lacks behind the proton transfer. After cyclization of the generated zwitterion 22a, the annulation product 11 is formed in an overall exergonic reaction.

The alternate regioisomer 13 could also be obtained from N,O-acetal intermediate 23. This pathway is identical to the one discussed for the formation of 11 for the transformation of 23 to 24. However, from there it continues with an almost isoenergetic isomerization of the N,O-acetal 24 to the N,O-acetal 27. This two-step process consists of elimination and subsequent addition of acetic acid through transition states TS06 and TS07.[18] In principle, 27 could also be obtained in a sequence of elimination and addition of AcOH (23 → 21b → 27, not shown in Scheme ), and we have calculated the transition states (ΔG⧧ = 30.8 and 29.9 kcal mol–1, respectively, Supporting Information) for these transformations as well. As they are significantly higher in energy than the barriers for the pathway involving 26 (Scheme ), we have to conclude that the azomethine ylide 21b does not lie on the reaction coordinate for the formation of either 11 or 13.

Next, the ammonium nitronate 28 is formed through TS08 before the rate-determining elimination of acetic acid takes place (TS09, ΔG⧧ = +30.8 kcal mol–1). Alternatively, zwitterions 22 could also be obtained directly from the azomethine ylide 26 through an intramolecular proton transfer. However, these reactions would occur with significantly higher barriers (ΔG⧧ = +40.4 kcal mol–1 for 26 → 22a and ΔG⧧ = +37.6 kcal mol–1 for 26 → 22b) and thus appear to play no role in this transformation. Finally, the thermodynamic product 13 is formed via cyclization of the zwitterion 22b.

The calculated energy profile is in good qualitative agreement with the experimental findings. The calculated barriers might be slightly overestimated as in the experimental studies both acetic acid and THIQ are used in excess. The results of eqs and 2 can also be rationalized using the computational data in Scheme . Although the energetic difference between both rate-determining steps TS05 and TS09 is rather small, the formation of 11 and 12 is kinetically preferred. The conditions of eq favor the formation of the kinetically preferred products 11 and 12, while the thermodynamically more stable product 13 is obtained exclusively at higher temperatures and longer reaction times.

Conclusions

We have reported the first examples of asymmetric redox-annulations of tetrahydroisoquinolines and tryptoline with readily available, highly enantioenriched 4-nitrobutyraldehydes. Reactions proceed under operationally convenient conditions and do not require the use of expensive catalysts. This strategy enabled the asymmetric preparation of polycyclic amines that contain the core structure of various bioactive compounds in just two steps from commercial materials. Simply by changing the reaction conditions, regioselective redox-annulations can be achieved at the nonbenzylic position of THIQ, enabling the rapid exploration of new chemical space.

Computational Methods

For the computational investigations, the conformational space for each structure was explored using the OPLS-2005 force field[19] and a modified Monte Carlo search algorithm implemented in MacroModel 10.6.[20] An energy cutoff of 20 kcal mol–1 was employed for the conformational analysis, and structures with heavy-atom root-mean-square deviations (RMSD) less than 2 Å after the initial force field optimizations were considered to be the same conformer. The remaining structures were subsequently optimized with the dispersion-corrected M06-L functional[21] with Grimme’s dispersion-correction D3[22] and the double-ζ basis set 6-31+G(d,p). Solvation by toluene was taken into account by using the integral equation formalism polarizable continuum model (IEFPCM)[23] for all calculations. Vibrational analysis verified that each structure was a minimum or transition state. Following the intrinsic reaction coordinates (IRC) confirmed that all transition states connected the corresponding reactants and products on the potential energy surface. Thermal corrections were obtained from unscaled harmonic vibrational frequencies at the same level of theory for a standard state of 1 mol L–1 and 298.15 K. Entropic contributions to the reported free energies were derived from partition functions evaluated with the quasiharmonic approximation by Truhlar and co-workers.[24] Electronic energies were subsequently obtained from single-point calculations of the M06-L-D3 geometries employing the meta-hybrid M06-2X functional,[25] Grimme’s dispersion-correction D3 (zero-damping), the large quadruple-ζ basis set def2-QZVP,[26] and IEFPCM for toluene, a level expected to give accurate energies.[27] An ultrafine grid was used throughout this study for numerical integration of the density. All density functional theory calculations were performed with Gaussian 09.[28]

Experimental Section

General Information

Starting materials, reagents, and solvents were purchased from commercial sources and used as received unless stated otherwise. Propionaldehyde, isovaleraldehyde, hydrocinnamaldehyde, and trans-cinnamaldehyde were purified by distillation prior to use. 1,2,3,4-Tetrahydroisoquinoline was distilled prior to use. Powdered molecular sieves (4 Å) were activated before use by heating in a furnace to 300 °C for 2 h and were stored in a desiccator. Nitroalkenes were prepared according to previously reported procedures.[29] Microwave reactions were carried out in a CEM Discover reactor. Silicon carbide (SiC) passive heating elements were purchased from Anton Paar. Analytical thin-layer chromatography was performed on EM Reagent 0.25 mm silica gel 60 F254 plates. Visualization was accomplished with UV light, potassium permanganate, and Dragendorff–Munier stains followed by heating. Purification of reaction products was carried out by flash column chromatography using Sorbent Technologies Standard grade silica gel (60 Å, 230–400 mesh). Chemical shifts in proton nuclear magnetic resonance spectra (1H NMR) are reported in ppm using the solvent as an internal standard (CDCl3 at 7.26 ppm, CD2Cl2 at 5.30 ppm). Data are reported as app = apparent, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, comp = complex, br = broad; coupling constant(s) in hertz. Chemical shifts in proton-decoupled carbon nuclear magnetic resonance spectra (13C NMR) are reported in ppm using the solvent as an internal standard (CDCl3 at 77.0 ppm, CD2Cl2 at 54.0 ppm). HRMS spectrometry data were recorded on a spectrometer operating on ESI-FTICR (MeCN as solvent). Optical rotations were measured using a 1 mL cell with a 1 dm path length at 589 nm and at 25 °C. (S)-Diphenylprolinol trimethylsilyl ether was prepared according to a literature procedure.[30]

General Procedures for the Synthesis of Starting Materials[10]

General Procedure A

To a stirred solution of nitroalkene (3 mmol, 1 equiv), (S)-diphenylprolinol trimethylsilyl ether (0.15 mmol, 5 mol %), and p-nitrophenol (0.15 mmol, 5 mol %) in toluene (3 mL) was added aldehyde (4.5 mmol, 1.5 equiv) at room temperature. The reaction progress was monitored by TLC. After completion, the reaction was quenched by the addition of 1 M HCl (10 mL) and the resulting mixture extracted with EtOAc (2 × 10 mL). The combined organic layers were dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography.

General Procedure B

To a stirred solution of trans-cinnamaldehyde (3 mmol, 1 equiv), (S)-diphenylprolinol trimethylsilyl ether (0.3 mmol, 10 mol %), and benzoic acid (0.6 mmol, 20 mol %) in MeOH (6 mL) was added nitromethane (9 mmol, 3 equiv) at room temperature. The reaction progress was monitored by TLC. After completion, the reaction was quenched by the addition of saturated NaHCO3 (10 mL) and the resulting mixture extracted with EtOAc (2 × 10 mL). The combined organic layers were dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography.

General Procedure C

To a stirred solution of nitroalkene (3 mmol, 1 equiv) and (S)-diphenylprolinol trimethylsilyl ether (0.3 mmol, 10 mol %) in dioxane (0.6 mL) was added acetaldehyde (30 mmol, 10 equiv) at 0 °C. The reaction mixture was stirred at room temperature, and the reaction progress was monitored by TLC. After completion, the reaction was quenched by the addition of 1 M HCl (10 mL) and the resulting mixture extracted with EtOAc (2 × 10 mL). The combined organic layers were dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography.

(2R,3S)-2-Methyl-4-nitro-3-phenylbutanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a yellow oil in 78% yield (mixture of two diastereomers). Compound 5a was previously reported, and its published characterization data matched our own in all respects.[10j] The enantiomeric excess was determined by HPLC with Daicel Chiralcel OD-H: n-hexane/i-PrOH = 90/10, flow rate = 1 mL/min, UV = 210 nm, tR = 22.4 min (minor) and tR = 32.9 min (major), 96% ee.

(2R,3S)-3-(4-Fluorophenyl)-2-methyl-4-nitrobutanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a yellow oil in 78% yield (mixture of two diastereomers). Compound 5b was previously reported, and its published characterization data matched our own in all respects.[10i]

(2R,3S)-3-(4-Bromophenyl)-2-methyl-4-nitrobutanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a yellow solid in 70% yield (mixture of two diastereomers). Compound 5c was previously reported, and its published characterization data matched our own in all respects.[10j]

(2R,3S)-2-Methyl-4-nitro-3-(p-tolyl)butanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a yellow oil in 70% yield (mixture of two diastereomers). Compound 5d was previously reported, and its published characterization data matched our own in all respects.[10c]

(2R,3S)-3-(4-Methoxyphenyl)-2-methyl-4-nitrobutanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a yellow oil in 68% yield (mixture of two diastereomers). Compound 5e was previously reported, and its published characterization data matched our own in all respects.[10j]

(2R,3R)-2-Methyl-3-(nitromethyl)-5-phenylpentanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a yellow oil in 57% yield (mixture of two diastereomers). Compound 5f was previously reported, and its published characterization data matched our own in all respects.[10j]

(2R,3S)-2-Benzyl-4-nitro-3-phenylbutanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a yellow oil in 66% yield (mixture of two diastereomers). Compound 5g was previously reported, and its published characterization data matched our own in all respects.[10j]

(2R,3S)-2-Isopropyl-4-nitro-3-phenylbutanal

The title compound was synthesized following general procedure A.[10j] The product was obtained as a white solid in 57% yield (mixture of two diastereomers). Compound 5h was previously reported, and its published characterization data matched our own in all respects.[10j]

(S)-4-Nitro-3-phenylbutanal

The title compound was synthesized following general procedure B.[10f] The product was obtained as a yellow oil in 74% yield. Compound 5k was previously reported, and its published characterization data matched our own in all respects.[10f] The product was reduced to the corresponding alcohol using NaBH4 for HPLC analysis:[31] Daicel Chiralcel OD-H, n-hexane/i-PrOH = 90/10, flow rate = 1 mL/min, UV = 230 nm, tR = 17.2 min (minor) and tR = 21.9 min (major), 95% ee.

(S)-3-(4-Chlorophenyl)-4-nitrobutanal

The title compound was synthesized following general procedure C.[10h] The product was obtained as a yellow oil in 44% yield. Compound 5l was previously reported, and its published characterization data matched our own in all respects.[10h]

(S)-3-(4-Bromophenyl)-4-nitrobutanal

The title compound was synthesized following general procedure C.[10h] The product was obtained as a yellow oil in 34% yield. Compound 5m was previously reported, and its published characterization data matched our own in all respects.[10h]

(S)-4-Nitro-3-(p-tolyl)butanal

The title compound was synthesized following general procedure C.[10h] The product was obtained as a yellow solid in 72% yield. Compound 5n was previously reported, and its published characterization data matched our own in all respects.[10h]

(S)-3-(4-Methoxyphenyl)-4-nitrobutanal

The title compound was synthesized following general procedure C.[10h] The product was obtained as a yellow oil in 56% yield. Compound 5o was previously reported, and its published characterization data matched our own in all respects.[10h]

(S)-3-(Naphthalen-2-yl)-4-nitrobutanal

The title compound was synthesized following general procedure C.[10h] The product was obtained as a yellow solid in 69% yield. Compound 5p was previously reported, and its published characterization data matched our own in all respects.[10h]

(R)-3-(Furan-2-yl)-4-nitrobutanal

The title compound was synthesized following general procedure C.[10h] The product was obtained as a yellow oil in 42% yield. Compound 5q was previously reported, and its published characterization data matched our own in all respects.[10h]

General Procedures for the Asymmetric Redox-Annulation

General Procedure A

To a mixture of aldehyde (0.6 mmol, 1 equiv), 4 Å MS (0.2 g) and AcOH (6 mmol, 10 equiv) in toluene (6 mL) was added the amine (1.2 mmol, 2 equiv) at room temperature. The mixture was heated under reflux for 1 h. Subsequently, the reaction mixture was allowed to cool to room temperature, diluted with EtOAc (20 mL), and washed with saturated aqueous NaHCO3 (3 × 10 mL). The combined aqueous layers were extracted with EtOAc (2 × 10 mL) and the combined organic layers dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography.

A solution of amine (1.2 mmol, 2 equiv) and 2-EHA (6 mmol, 10 equiv) in xylenes (6 mL) was heated under reflux. The aldehyde (0.6 mmol, 0.12 M solution in xylenes) was delivered through the top of the reflux condenser over 15 h via syringe pump. The reaction was then kept under reflux for a further 0.5–1 h at which time the aldehyde was consumed as judged by TLC analysis. Subsequently, the reaction mixture was allowed to cool to room temperature, diluted with EtOAc (20 mL), and washed with saturated aqueous NaHCO3 (3 × 20 mL). The combined aqueous layers were extracted with EtOAc (2 × 10 mL) and the combined organic layers dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography.

A 10 mL microwave reaction tube was charged with a 10 × 8 mm SiC passive heating element, aldehyde (0.6 mmol, 1 equiv), toluene (6 mL), amine (1.2 mmol, 2 equiv), 3 Å MS (0.2 g), and AcOH (6 mmol, 10 equiv). The reaction tube was sealed with a Teflon-lined snap cap and heated in a microwave reactor at 120 °C (0–15 psi) for 3 min. After being cooled with compressed air flow, the reaction mixture was diluted with EtOAc (20 mL) and washed with saturated aqueous NaHCO3 (3 × 20 mL). The combined aqueous layers were extracted with EtOAc (2 × 10 mL) and the combined organic layers dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography.

Products 6a and 7a

Following general procedure A, products 6a and 7a were obtained in a 2:1 ratio (71% combined yield). The relative stereochemistry was determined by GCOSY and NOESY NMR.

Characterization data for 6a:

yellowish oil; R = 0.32 in 20% EtOAc/Hex; [α]D25 – 31.9 (c 0.5, CHCl3); IR (KBr) 3063, 3028, 2959, 2927, 2828, 1539, 1492, 1452, 1311, 1264, 1153, 1094, 750, 703 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.33–7.28 (comp, 2H), 7.27–7.25 (m, 1H), 7.19–7.15 (comp, 4H), 7.07 (app t, J = 7.5 Hz, 1H), 6.87 (app d, J = 7.8 Hz, 1H), 4.97 (dd, J = 11.2, 9.8 Hz, 1H), 4.39 (d, J = 9.8 Hz, 1H), 3.34 (ddd, J = 11.4, 9.8, 4.9 Hz, 1H), 3.19 (dd, J = 13.7, 4.1 Hz, 1H), 3.11 (app t, J = 11.4 Hz, 1H), 3.05 (dd, J = 9.6, 6.7 Hz, 1H), 3.00–2.98 (m, 1H), 2.96–2.92 (comp, 2H), 2.30–2.23 (m, 1H), 0.73 (d, J = 6.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 138.2(2), 134.2(1), 132.9, 129.5, 129.1, 128.1, 128.0, 127.0, 126.3, 91.7, 77.6, 77.3, 77.1, 63.0, 62.1, 56.0, 46.5, 31.2, 29.9, 16.7; HRMS (ESI) m/z calcd for C20H23N2O2 [M + H]+ 323.1754, found 323.1765; HPLC Daicel Chiralcel OD-H, n-hexane/i-PrOH = 90/10, flow rate = 1 mL/min; UV = 230 nm, tR = 7.1 min (major) and tR = 8.0 min (minor), 95% ee.

Characterization data for 7a

yellowish solid; mp 180–182 °C; R = 0.46 in 20% EtOAc/Hex; [α]D25 −130.8 (c 0.5, CHCl3); IR (KBr) 3061, 3031, 2957, 2957, 2927, 2893, 2811, 2767, 1546, 1489, 1452, 1351, 1299, 1146, 1111, 738, 696 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.32–7.29 (comp, 2H), 7.27–7.20 (comp, 2H), 7.20–7.14 (comp, 3H), 7.11 (app t, J = 7.6 Hz, 1H), 6.90 (app d, J = 7.9 Hz, 1H), 5.09 (dd, J = 11.7, 9.0 Hz, 1H), 4.20 (d, J = 9.0 Hz, 1H), 3.82 (dd, J = 11.7, 5.0 Hz, 1H), 3.25 (dd, J = 12.2, 3.5 Hz, 1H), 3.12 (ddd, J = 14.8, 9.4, 5.0 Hz, 1H), 3.05 (app dt, J = 10.9, 4.4 Hz, 1H), 2.98 (dd, J = 12.2, 1.8 Hz, 1H), 2.86 (ddd, J = 11.1, 9.4, 3.5 Hz, 1H), 2.76 (app dt, J = 15.4, 3.5 Hz, 1H), 2.18–2.09 (m, 1H), 0.95 (d, J = 7.2 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 138.5, 136.0, 133.0, 129.5, 128.7, 128.2, 127.6, 127.5, 126.5, 126.3, 88.3, 66.0, 62.0, 52.7, 50.8, 35.8, 31.2, 15.2; m/z (ESI-MS) 323.2 [M + H]+; HPLC Daicel Chiralcel OD-H, n-hexane/i-PrOH = 90/10, flow rate = 1 mL/min; UV = 230 nm, tR = 6.3 min (minor) and tR = 6.9 min (major), 95% ee.

Products 6b and 7b

Following general procedure A, products 6b and 7b were obtained in a 2:1 ratio (68% combined yield).

Characterization data for 6b:

yellowish oil; R = 0.32 in 20% EtOAc/Hex; [α]D25 −32.6 (c 0.5, CHCl3); IR (KBr) 3066, 3033, 2959, 2920, 2843, 1608, 1543, 1509, 1457, 1363, 1311, 1225, 1161, 1096, 733 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.23–7.18 (m, 1H), 7.16–7.13 (comp, 3H), 7.07 (app t, J = 7.5 Hz, 1H), 7.01–6.98 (comp, 2H), 6.85 (app d, J = 7.8 Hz, 1H), 4.90 (dd, J = 11.2, 9.8 Hz, 1H), 4.37 (d, J = 9.8 Hz, 1H), 3.32 (ddd, J = 11.2, 9.4, 4.9 Hz, 1H), 3.18 (dd, J = 13.7, 4.1 Hz, 1H), 3.10 (app t, J = 11.2 Hz, 1H), 3.03 (dd, J = 9.8, 6.7 Hz, 1H), 2.99–2.90 (comp, 3H), 2.25–2.17 (m, 1H), 0.72 (d, J = 6.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 162.4 (d, J = 246.2 Hz), 134.2, 134.0 (d, J = 3.3 Hz), 132.8, 129.6, 128.2, 126.9, 126.4(0), 126.3(6), 116.1 (d, J = 21.5 Hz), 91.8, 63.0, 62.0, 55.3, 46.5, 31.3, 29.9, 16.6; m/z (ESI-MS) 341.1 [M + H]+.

Characterization data for 7b

Yellowish solid; mp 100–103 °C; (R = 0.47 in 20% EtOAc/Hex); [α]D25 −126.5 (c 0.5, CHCl3); IR (KBr) 3063, 2969, 2935, 2910, 2814, 2769, 1608, 1546, 1506, 1427, 1348, 1299, 1222, 1161, 1109, 842, 812, 753, 696 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.21 (app t, J = 7.3 Hz, 1H), 7.18–7.09 (comp, 4H), 7.01–6.98 (comp, 2H), 6.88 (app d, J = 7.9 Hz, 1H), 5.02 (dd, J = 11.7, 9.0 Hz, 1H), 4.17 (d, J = 9.0 Hz, 1H), 3.80 (dd, J = 11.7, 4.9 Hz, 1H), 3.22 (dd, J = 12.2, 3.2 Hz, 1H), 3.12 (ddd, J = 14.6, 9.3, 4.6 Hz, 1H), 3.02 (app dt, J = 10.9, 4.6 Hz, 1H), 2.96 (dd, J = 12.2, 1.7 Hz, 1H), 2.84 (app td, J = 10.9, 3.2 Hz, 1H), 2.74 (app dt, J = 15.5, 3.2 Hz, 1H), 2.15–2.05 (m, 1H), 0.94 (d, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 162.2 (d, J = 245.9 Hz), 136.1, 134.2(9), 134.2(6), 133.0, 129.7 (d, J = 8.0 Hz), 129.5, 127.6, 126.5, 126.2, 115.7 (d, J = 21.4 Hz), 88.6, 66.0, 61.9, 52.1, 50.8, 35.8, 31.2, 15.0; m/z (ESI-MS) 341.1 [M + H]+.

Products 6c and 7c

Following general procedure A, products 6c and 7c were obtained in a 2:1 ratio (71% combined yield).

Characterization data for 6c:

yellowish solid; mp 130–132 °C; R = 0.37 in 20% EtOAc/Hex; [α]D25 −38.6 (c 0.5, CHCl3); IR (KBr) 3058, 3024, 2954, 2920, 2831, 1731, 1546, 1484, 1452, 1371, 1304, 1245, 1143, 1099, 1074, 1012, 958, 889, 817, 738, 674 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.45–7.40 (comp, 2H), 7.20 (app t, J = 7.4 Hz, 1H), 7.17–7.13 (m, 1H), 7.09–7.05 (comp, 3H), 6.85 (app d, J = 7.9 Hz, 1H), 4.90 (app t, J = 9.7 Hz, 1H), 4.36 (d, J = 9.7 Hz, 1H), 3.31 (ddd, J = 11.6, 10.9, 4.5 Hz, 1H), 3.18 (dd, J = 13.7, 3.9 Hz, 1H), 3.09 (app t, J = 11.6 Hz, 1H), 3.05–3.01 (m, 1H), 2.99–2.89 (comp, 3H), 2.25–2.16 (m, 1H), 0.72 (d, J = 6.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 137.3, 134.2, 132.7, 132.3, 129.6, 128.2, 126.9, 126.4, 121.9, 91.5, 63.0, 62.0, 55.5, 46.5, 31.2, 29.9, 16.6; m/z (ESI-MS) (79Br) 401.1 [M + H]+, (81Br) 403.1 [M + H]+.

Characterization data for 7c:

yellowish solid; mp 185–190 °C; R = 0.48 in 20% EtOAc/Hex; [α]D25 −134.9 (c 0.5, CHCl3); IR (KBr) 3061, 3026, 2964, 2927, 2895, 2809, 2764, 1541, 1492, 1447, 1425, 1351, 1291, 1148, 1109, 1072, 1037, 1007, 837, 807, 731 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.45–7.41(comp, 2H), 7.21 (app t, J = 7.4 Hz, 1H), 7.17–7.14 (m, 1H), 7.11 (app t, J = 7.6 Hz, 1H), 7.07–7.03 (comp, 2H), 6.87 (app d, J = 7.9 Hz, 1H), 5.02 (dd, J = 11.6, 9.0 Hz, 1H), 4.18 (d, J = 9.0 Hz, 1H), 3.78 (dd, J = 11.6, 4.9 Hz, 1H), 3.22 (dd, J = 12.2, 3.2 Hz, 1H), 3.11 (ddd, J = 14.8, 9.3, 4.7 Hz, 1H), 3.07–3.00 (m, 1H), 2.98–2.94 (m, 1H), 2.89–2.81 (m, 1H), 2.78–2.70 (m, 1H), 2.14–2.06 (m, 1H), 0.94 (d, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 137.6, 136.1, 132.9(0), 131.9(2), 129.9, 129.6, 127.7, 126.5, 126.2, 121.5, 88.3, 66.0, 61.9, 52.3, 50.8, 35.7, 31.2, 15.0; m/z (ESI-MS) (79Br) 401.1 [M + H]+, (81Br) 403.1 [M + H]+.

Products 6d and 7d

Following general procedure A, products 6d and 7d were obtained in a 2:1 ratio (69% combined yield).

Characterization data for 6d:

yellowish oil; R = 0.35 in 20% EtOAc/Hex; [α]D25 −34.8 (c 0.5, CHCl3); IR (KBr) 3056, 3021, 2972, 2925, 2905, 2878, 2809, 2767, 1548, 1509, 1492, 1445, 1371, 1346, 1296, 1267, 1254, 1151, 1114, 1037, 951, 832, 802, 733 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.22–7.18 (m, 1H), 7.17–7.14 (m, 1H), 7.13–7.09 (comp, 2H), 7.09–7.04 (comp, 3H), 6.87 (app d, J = 7.9 Hz, 1H), 4.94 (dd, J = 11.2, 9.8 Hz, 1H), 4.38 (d, J = 9.8 Hz, 1H), 3.34 (ddd, J = 11.2, 9.6, 4.9 Hz, 1H), 3.18 (dd, J = 13.7, 4.1 Hz, 1H), 3.11–3.01 (comp, 2H), 3.00–2.91 (comp, 3H), 2.31 (s, 3H), 2.28–2.21 (m, 1H), 0.73 (d, J = 6.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 137.5, 135.2, 134.2, 133.0, 129.8, 129.5, 128.1, 127.0, 126.3, 105.0, 91.8, 63.0, 62.1, 55.7, 46.4, 31.2, 29.9, 21.3, 16.7; m/z (ESI-MS) 337.2 [M + H]+.

Characterization data for 7d:

yellowish oil; R = 0.52 in 20% EtOAc/Hex; [α]D25 −157.6 (c 0.5, CHCl3); IR (KBr) 3056, 3024, 2962, 2920, 2895, 2809, 2767, 1546, 1509, 1494, 1450, 1368, 1348, 1294, 1264, 1148, 1114, 1039, 948, 837, 800, 726 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.23–7.19 (m, 1H), 7.17–7.14 (m, 1H), 7.12–7.10 (comp, 3H), 7.09–7.05 (comp, 2H), 6.90 (app d, J = 7.9 Hz, 1H), 5.07 (dd, J = 11.7, 9.0 Hz, 1H), 4.18 (d, J = 9.0 Hz, 1H), 3.78 (dd, J = 11.7, 4.9 Hz, 1H), 3.23 (dd, J = 12.2, 3.3 Hz, 1H), 3.12 (ddd, J = 14.8, 9.3, 4.9 Hz, 1H), 3.04 (app dt, J = 11.1, 4.4 Hz, 1H), 2.97 (dd, J = 12.2, 1.8 Hz, 1H), 2.85 (ddd, J = 11.1, 9.3, 3.5 Hz, 1H), 2.75 (app dt, J = 15.5, 3.5 Hz, 1H), 2.31 (s, 3H), 2.13–2.10 (m, 1H), 0.96 (d, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 137.1, 136.1, 135.5, 133.2, 129.5, 129.4, 128.1, 127.6, 126.5, 126.3, 88.5, 66.0, 62.0, 52.4, 50.8, 35.9, 31.3, 21.3, 15.2; m/z (ESI-MS) 337.2 [M + H]+.

Products 6e and 7e

Following general procedure A, products 6e and 7e were obtained in a 1.5:1 ratio (65% combined yield).

Characterization data for 6e:

yellowish solid; mp 110–113 °C; R = 0.24 in 20% EtOAc/Hex; [α]D25 −24.5 (c 0.5, CHCl3); IR (KBr) 2954, 2932, 2902, 2833, 2804, 1615, 1546, 1541, 1462, 1380, 1249, 1175, 1116, 1035, 837, 740 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.21–7.17 (m, 1H), 7.16–7.14 (m, 1H), 7.09–7.05 (comp, 3H), 6.86–6.82 (comp, 3H), 4.90 (dd, J = 11.0, 9.8 Hz, 1H), 4.37 (d, J = 9.8 Hz, 1H), 3.77 (s, 3H), 3.33 (ddd, J = 11.3, 9.8, 4.9 Hz, 1H), 3.18 (dd, J = 13.7, 4.1 Hz, 1H), 3.09–3.01 (comp, 2H), 2.99–2.90 (comp, 3H), 2.26–2.17 (m, 1H), 0.73 (d, J = 6.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 159.2, 134.1, 132.9, 130.2, 129.5, 128.1, 126.9, 126.3, 114.5, 91.9, 62.9, 62.1, 55.4, 55.2, 46.5, 31.3, 29.9, 16.7; m/z (ESI-MS) 353.2 [M + H]+.

Characterization data for 7e:

yellowish solid; mp 120–122 °C; R = 0.41 in 20% EtOAc/Hex; [α]D25 −178.1 (c 0.5, CHCl3); IR (KBr) 2954, 2927, 2833, 1613, 1543, 1506, 1452, 1361, 1341, 1247, 1180, 1027, 820, 745 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.22–7.18 (m, 1H), 7.16–7.15 (m, 1H), 7.12–7.09 (comp, 3H), 6.89 (app d, J = 7.9 Hz, 1H), 6.85–6.81 (comp, 2H), 5.03 (dd, J = 11.5, 9.2 Hz, 1H), 4.19 (d, J = 9.2 Hz, 1H), 3.78 (s, 3H), 3.76 (dd, J = 8.0, 4.9 Hz, 1H), 3.24–3.22 (m, 1H), 3.11 (ddd, J = 14.6, 9.1, 4.7 Hz, 1H), 3.08–3.02 (m, 1H), 2.98–2.95 (m, 1H), 2.87–2.84 (m, 1H), 2.78–2.75 (m, 1H), 2.15–2.04 (m, 1H), 0.95 (d, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 158.9, 136.0, 133.2, 130.5, 129.5, 129.2, 127.6, 126.5, 126.3, 114.1, 88.6, 65.9, 61.9, 55.4, 52.0, 50.8, 35.9, 31.1, 15.2; m/z (ESI-MS) 353.1 [M + H]+.

Products 6f and 7f

Following general procedure A, products 6f and 7f were obtained in a 1:1 ratio (48% combined yield).

Characterization data for 6f:

yellowish oil; R = 0.28 in 10% EtOAc/Hex; [α]D25 −37.4 (c 0.5, CHCl3); IR (KBr) 3061, 3024, 2952, 2920, 2870, 1598, 1541, 1497, 1452, 1371, 1314, 1272, 1143, 1096, 941, 750, 698 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.30–7.26 (comp, 2H), 7.24–7.17 (comp, 2H), 7.18–7.12 (comp, 3H), 7.10 (app td, J = 7.6, 1.5 Hz, 1H), 6.89 (app d, J = 7.8 Hz, 1H), 4.82 (dd, J = 11.2, 9.9 Hz, 1H), 4.30 (d, J = 9.9 Hz, 1H), 3.17 (ddd, J = 11.4, 9.9, 4.6 Hz, 1H), 3.09–2.99 (comp, 2H), 2.92 (app dt, J = 16.3, 3.9 Hz, 1H), 2.88–2.81 (comp, 2H), 2.64–2.50 (comp, 2H), 2.21–2.15 (m, 1H), 2.06–1.96 (m, 1H), 1.94–1.85 (m, 1H), 1.62–1.55 (m, 1H), 1.01 (d, J = 6.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 141.7, 134.2, 133.2, 129.6, 128.7, 128.5, 128.1, 126.9, 126.3, 89.5, 62.8, 62.0, 47.4, 46.2, 30.9, 30.8, 29.8, 27.5, 16.3; m/z (ESI-MS) 351.2 [M + H]+.

Characterization data for 7f:

yellowish oil; R = 0.42 in 10% EtOAc/Hex; [α]D25 −91.8 (c 0.5, CHCl3); IR (KBr) 3063, 3031, 2930, 2891, 2809, 2767, 1605, 1536, 1498, 1455, 1356, 1299, 1245, 1146, 1104, 736, 694 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.29–7.32 (comp, 2H), 7.23–7.20 (m, 1H), 7.19–7.17 (comp, 3H), 7.13–7.09 (comp, 2H), 6.91 (app d, J = 7.9 Hz, 1H), 4.41 (dd, J = 11.0, 9.2 Hz, 1H), 4.05 (d, J = 9.2 Hz, 1H), 3.09–3.03 (m, 1H), 3.00 (dd, J = 12.2, 3.4 Hz, 1H), 2.98–2.94 (m, 1H), 2.90 (dd, J = 12.2, 2.3 Hz, 1H), 2.81–2.74 (comp, 2H), 2.74–2.67 (m, 1H), 2.54–2.48 (m, 1H), 2.48–2.40 (m, 1H), 2.21–2.15 (m, 1H), 1.71–1.62 (m, 1H), 1.60–1.53 (m, 1H), 1.12 (d, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 141.4, 136.1, 133.6, 129.5, 128.7, 128.5, 127.5, 126.5, 126.3, 125.9, 91.5, 77.5, 77.3, 77.0, 65.2, 61.8, 50.9, 44.7, 32.3, 31.1, 30.4, 29.9, 13.8; m/z (ESI-MS) 351.2 [M + H]+.

Products 6g and 7g

Following general procedure A, products 6g and 7g were obtained in a 1.8:1 ratio (70% combined yield).

Characterization data for 6g:

yellowish solid; mp 64–66 °C; R = 0.27 in 10% EtOAc/Hex; [α]D25 −61.4 (c 0.5, CHCl3); IR (KBr) 3063, 3026, 2917, 2851, 2754, 1600, 1543, 1492, 1452, 1368, 1311, 1257, 1143, 1099, 738, 696 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.38–7.35 (comp, 2H), 7.31–7.23 (comp, 5H), 7.20–7.17 (comp, 2H), 7.14–7.11 (m, 1H), 7.07 (app t, J = 7.5 Hz, 1H), 7.01–6.99 (comp, 2H), 6.86 (app d, J = 7.8 Hz, 1H), 4.94 (app t, J = 10.4 Hz, 1H), 4.36 (d, J = 9.7 Hz, 1H), 3.29 (app t, J = 11.4 Hz, 1H), 3.21–3.16 (m, 1H), 3.09 (dd, J = 13.7, 4.0 Hz, 1H), 2.98–2.87 (comp, 3H), 2.75 (app dt, J = 10.6, 5.0 Hz, 1H), 2.60 (dd, J = 13.7, 2.8 Hz, 1H), 2.50–2.38 (m, 1H), 2.16 (dd, J = 13.7, 10.5 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 139.4, 138.0, 134.4, 132.8, 129.5, 129.3, 129.0, 128.7, 128.3, 128.0, 126.8, 126.5, 126.4, 92.5, 63.1, 59.4, 54.7, 46.7, 38.3, 37.8, 29.9; m/z (ESI-MS) 399.2 [M + H]+.

Characterization data for 7g:

yellowish oil; R = 0.48 in 10% EtOAc/Hex; [α]D25 −156.6 (c 0.5, CHCl3); IR (KBr) 3061, 3024, 2952, 2927, 2902, 2804, 2754, 1600, 1546, 1492, 1452, 1356, 1299, 1252, 1143, 760, 701 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.37–7.34 (comp, 2H), 7.31–7.21 (comp, 6H), 7.21–7.17 (comp, 2H), 7.17–7.11 (m, 1H), 6.97–6.95 (comp, 2H), 6.91 (d, J = 7.9 Hz, 1H), 5.16 (dd, J = 11.7, 8.9 Hz, 1H), 4.21 (d, J = 8.9 Hz, 1H), 3.97 (dd, J = 11.7, 4.9 Hz, 1H), 3.26 (ddd, J = 14.7, 10.7, 4.9 Hz, 1H), 2.87 (dd, J = 7.9, 3.0 Hz, 1H), 2.84 (dd, J = 6.9, 2.5 Hz, 1H), 2.83–2.79 (comp, 2H), 2.78–2.70 (comp, 2H), 2.46 (dd, J = 13.0, 3.5 Hz, 1H), 2.23–2.17 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 140.9, 138.1, 136.3, 133.2, 129.6, 129.2, 128.9, 128.6, 128.3, 127.7, 127.6, 126.6, 126.3, 126.1, 89.2, 66.5, 57.1, 52.9, 50.8, 43.3, 33.2, 31.6; m/z (ESI-MS) 399.2 [M + H]+.

Products 6h and 7h

Following general procedure A, products 6h and 7h were obtained in a 5:1 ratio (37% combined yield).

Characterization data for 6h:

yellowish solid; mp 180–184 °C; R = 0.45 in 20% EtOAc/Hex; [α]D25 −23.0 (c 0.5, CHCl3); IR (KBr) 3063, 3026, 2952, 2922, 2868, 2823, 1546, 1497, 1450, 1368, 1306, 1141, 1099, 1005, 750, 726, 696 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.32–7.29 (comp, 2H), 7.25–7.23 (m, 1H), 7.21–7.14 (comp, 4H), 7.07 (app t, J = 7.5 Hz, 1H), 6.85 (app d, J = 7.9 Hz, 1H), 4.92 (app t, J = 9.8 Hz, 1H), 4.35 (d, J = 9.8 Hz, 1H), 3.42 (app t, J = 11.6 Hz, 1H), 3.38–3.29 (m, 1H), 3.19 (dd, J = 13.4, 3.7 Hz, 1H), 3.13–2.96 (comp, 3H), 2.94–2.87 (m, 1H), 2.24–2.15 (m, 1H), 1.50–1.44 (m, 1H), 0.90 (d, J = 7.0 Hz, 3H), 0.83 (d, J = 7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 138.0, 134.2, 132.9, 129.5, 129.2, 128.1, 128.0, 126.9, 126.4, 93.0, 62.9, 54.1, 52.2, 46.7, 40.3, 29.9, 26.6, 21.5, 15.6; m/z (ESI-MS) 351.2 [M + H]+.

Products 6i and 7i

Following general procedure A, products 6i and 7i were obtained in a 1.5:1 ratio (66% combined yield).

Characterization data for 6i:

yellowish solid; mp 145–148 °C; R = 0.35 in 30% EtOAc/Hex; [α]D25 −11.9 (c 0.5, CHCl3); IR (KBr) 3063, 3026, 3001, 2957, 2922, 2902, 2828, 1610, 1539, 1504, 1452, 1378, 1309, 1252, 1146, 1035, 859, 817, 760, 743, 701 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.31–7.28 (comp, 2H), 7.27–7.21 (m, 1H), 7.17–7.16 (comp, 2H), 6.78 (app d, J = 8.6 Hz, 1H), 6.68–6.65 (m, 1H), 6.62 (dd, J = 8.6, 2.5 Hz, 1H), 4.92 (dd, J = 11.2, 9.8 Hz, 1H), 4.32 (d, J = 9.7 Hz, 1H), 3.75 (s, 3H), 3.35–3.26 (m, 1H), 3.17 (dd, J = 13.7, 4.1 Hz, 1H), 3.08 (app t, J = 11.4 Hz, 1H), 3.05–2.98 (m, 1H), 2.97–2.87 (comp, 3H), 2.30–2.18 (m, 1H), 0.71 (d, J = 6.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 159.2, 138.2, 135.7, 129.1, 128.0, 128.0, 125.3, 114.4, 112.2, 91.9, 62.6, 62.1, 55.9, 55.4, 46.4, 31.2, 30.2, 16.7; m/z (ESI-MS) 353.1 [M + H]+.

Characterization data for 7i:

yellowish solid; mp 130–133; R = 0.45 in 30% EtOAc/Hex; [α]D25 −102.0 (c 0.5, CHCl3); IR (KBr) 3061, 3028, 2959, 2932, 2907, 2863, 2806, 2767, 1613, 1546, 1494, 1455, 1356, 1269, 1151, 1116, 1039, 827, 743, 698 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.31–7.28 (comp, 2H), 7.27–7.21 (m, 1H), 7.18–7.15 (comp, 2H), 6.81 (app d, J = 8.2 Hz, 1H), 6.68–6.66 (comp, 2H), 5.05 (dd, J = 11.6, 9.0 Hz, 1H), 4.13 (d, J = 9.0 Hz, 1H), 3.80 (dd, J = 10.2, 5.0 Hz. 1H), 3.78 (s, 3H), 3.22 (dd, J = 12.2, 3.0 Hz, 1H), 3.09 (ddd, J = 14.8, 9.2, 4.5 Hz, 1H), 3.05–2.99 (m, 1H), 2.96 (app d, J = 12.2 Hz, 1H), 2.83 (ddd, J = 12.2, 10.2, 3.3 Hz, 1H), 2.74–2.66 (m, 1H), 2.16–2.07 (m, 1H) 0.94 (d, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 158.8, 138.6, 137.6, 128.7, 128.2, 127.5, 127.4, 125.4, 114.4, 112.2, 88.5, 65.8, 62.0, 55.4, 52.6, 50.7, 35.9, 31.5, 15.1; m/z (ESI-MS) 353.1 [M + H]+.

Products 6j and 7j

Following general procedure A, products 6j and 7j were obtained in a 2:1 ratio (42% combined yield).

Characterization data for 6j:

yellowish oil; R = 0.36 in 20% EtOAc/Hex; [α]D25 −17.5 (c 0.5, CHCl3); IR (KBr) 3407, 3058, 3026, 2952, 2905, 2838, 2806, 1724, 1548, 1492, 1450, 1378, 1361, 1267, 1165, 740, 698 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.59 (br s, 1H), 7.50 (app d, J = 7.5 Hz, 1H), 7.35–7.32 (comp, 3H), 7.31–7.27 (m, 1H), 7.19–7.14 (comp, 3H), 7.13–7.07 (m, 1H), 4.91–4.87 (m, 1H), 4.26 (d, J = 9.4 Hz, 1H), 3.23–3.18 (m, 2H), 3.05–2.93 (comp, 2H), 2.90–2.81 (comp, 2H), 2.69–2.61 (m, 1H), 2.35–2.21 (m, 1H), 0.77 (d, J = 6.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 137.5, 136.8, 129.2, 128.3, 126.7, 122.7, 120.0, 118.5, 111.6, 111.2, 93.2, 62.7, 61.8, 56.5, 51.3, 34.9, 22.1, 16.9; HRMS (ESI) m/z calcd for C22H24N3O2 [M + H]+ 362.1863, found 362.1875.

Characterization data for 7j:

yellowish solid; mp 160–163 °C; R = 0.40 in 20% EtOAc/Hex; [α]D25 −25.7 (c 0.5, CHCl3); IR (KBr) 3409, 3061, 3031, 2964, 2898, 2838, 2774, 1697, 1632, 1541, 1452, 1343, 1269, 1170, 1114, 1072, 1007, 968, 736, 696 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.61 (br s, 1H), 7.51 (app d, J = 7.8 Hz, 1H), 7.35–7.32 (comp, 2H), 7.28 (app d, J = 7.3 Hz, 1H), 7.24–7.21 (comp, 2H), 7.20–7.15 (m, 1H), 7.13–7.09 (m, 1H), 5.28 (dd, J = 11.8, 9.4 Hz, 1H), 4.18–4.12 (m, 1H), 3.72 (dd, J = 11.8, 4.5 Hz, 1H), 3.15–3.07 (comp, 2H), 3.06–2.97 (comp, 2H), 2.88–2.74 (comp, 2H), 2.22–2.14 (m, 1H), 1.01 (d, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 136.9, 128.8, 128.4, 127.8, 126.7, 122.7, 120.0, 118.5, 111.6, 87.7, 63.8, 62.1, 52.9, 52.7, 35.9, 22.1, 14.5; m/z (ESI-MS) 362.2 [M + H]+.

Product 6k

Following general procedure A, product 6k was obtained in 61% yield. The relative stereochemistry was determined by GCOSY and NOESY NMR.

Characterization data for 6k:

yellowish solid; mp 150–152 °C; R = 0.42 in 30% EtOAc/Hex; [α]D25 −56.3 (c 0.5, CHCl3); IR (KBr) 3059, 3028, 2931, 2862, 2862, 2834, 1714, 1630, 1551, 1489, 1447, 1364, 1036, 1143, 1108, 1081, 752, 700 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.33–7.30 (comp, 2H), 7.29–7.19 (comp, 4H), 7.18–7.14 (m, 1H), 7.08 (app t, J = 7.3 Hz, 1H), 6.87 (app d, J = 7.8 Hz, 1H), 4.97 (dd, J = 11.1, 9.8 Hz, 1H), 4.37 (d, J = 9.8 Hz, 1H), 3.56 (app td, J = 12.7, 4.4 Hz, 1H), 3.38–3.22 (comp, 3H), 3.07 (ddd, J = 15.8, 9.3, 6.3 Hz, 1H), 2.98 (app dt, J = 16.4, 4.1 Hz, 1H), 2.90 (ddd, J = 9.9, 6.1, 3.6 Hz, 1H), 2.17–2.09 (m, 1H), 1.83–1.77 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 139.9, 134.2, 133.0, 129.5, 129.2, 128.1, 128.0, 127.5, 127.0, 126.3, 91.0, 63.1, 54.5, 49.0, 45.9, 29.8, 28.2; m/z (ESI-MS) 309.1 [M + H]+; HPLC Daicel Chiralcel OD-H, n-hexane/i-PrOH = 90/10, flow rate = 1 mL/min, UV = 230 nm, tR = 11.1 min (major) and tR = 13.9 min (minor), 94% ee.

Product 6l

Following general procedure A, product 6l was obtained in 51% yield.

Characterization data for 6l:

yellowish solid; mp 150–152 °C; R = 0.31 in 30% EtOAc/Hex; [α]D25 −50.1 (c 0.5, CHCl3); IR (KBr) 3021, 2941, 2914, 2845, 2824, 1644, 1541, 1485, 1369, 1309, 1143, 1102, 1067, 1105, 811, 766, 755 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.31–7.27 (comp, 2H), 7.24–7.19 (m, 1H), 7.17–7.15 (comp, 3H), 7.08 (app t, J = 7.2 Hz, 1H), 6.85 (app d, J = 7.8 Hz, 1H) 4.91 (app t, J = 9.6 Hz, 1H), 4.37 (d, J = 9.6 Hz, 1H), 3.54 (app td, J = 12.8, 4.4 Hz, 1H), 3.37–3.22 (comp, 3H), 3.11–3.03 (m, 1H), 3.01–2.97 (m, 1H), 2.91 (ddd, J = 10.1, 5.9, 3.9 Hz, 1H), 2.15–2.05 (m, 1H), 1.83–1.76 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 138.2, 134.1, 133.9, 132.5, 129.6, 129.4, 128.8, 128.3, 126.9, 126.4, 90.9, 63.0, 54.4, 48.3, 46.1, 29.7, 28.1; m/z (ESI-MS) (35Cl) 343.2 [M + H]+, (37Cl) 345.2 [M + H]+.

Product 6m

Following general procedure A, product 6m was obtained in 55% yield.

Characterization data for 6m:

yellowish solid; mp 150–153 °C; R = 0.31 in 30% EtOAc/Hex; [α]D25 −48.9 (c 0.5, CHCl3); IR (KBr) 3021, 2941, 2914, 2855, 2824, 1644, 1541, 1485, 1451, 1364, 1309, 1143, 1102, 1067, 1105, 811, 766, 749 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.46–7.40 (comp, 2H), 7.24–7.18 (m, 1H), 7.16 (d, J = 7.1 Hz, 1H), 7.12–7.05 (comp, 3H), 6.84 (app d, J = 7.8 Hz, 1H), 4.89 (dd, J = 11.2, 9.6 Hz, 1H), 4.34 (d, J = 9.6 Hz, 1H), 3.53 (app td, J = 12.8, 4.4 Hz, 1H), 3.34–3.18 (comp, 3H), 3.04 (ddd, J = 15.5, 9.1, 6.2 Hz, 1H), 2.97 (app dt, J = 16.3, 4.2 Hz, 1H), 2.92–2.85 (m, 1H), 2.11–2.02 (m, 1H), 1.79–1.75 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 138.9, 134.2, 132.8, 132.3, 129.6, 129.2, 128.2, 126.9, 126.3, 121.9, 90.8, 63.1, 54.4, 48.5, 46.0, 29.8, 28.2; m/z (ESI-MS) (79Br) 387.1 [M + H]+, (81Br) 389.1 [M + H]+.

Product 6n

Following general procedure A, product 6n was obtained in 64% yield.

Characterization data for 6n:

yellowish solid; mp 154–156 °C; R = 0.48 in 30% EtOAc/Hex; [α]D25 −29.6 (c 0.5, CHCl3); IR (KBr) 3021, 2948, 2917, 2855, 2824, 1648, 1548, 1510, 1364, 1306, 1140, 1102, 1067, 1036, 942, 804, 752 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.23–7.20 (m, 1H), 7.19–7.16 (m, 1H), 7.14–7.11 (comp, 4H), 7.08 (app t, J = 7.5 Hz, 1H), 6.88 (app d, J = 7.9 Hz, 1H), 4.99–4.89 (m, 1H), 4.37 (d, J = 9.6 Hz, 1H), 3.58–3.48 (m, 1H), 3.36–3.30 (m, 1H), 3.28 (dd, J = 13.2, 2.1 Hz, 1H), 3.26–3.21 (m, 1H), 3.10–3.04 (m, 1H), 3.02–2.95 (m, 1H), 2.91–2.87 (m, 1H), 2.32 (s, 3H), 2.17–2.06 (m, 1H), 1.83–1.73 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 137.6, 137.0, 134.2, 133.1, 129.9, 129.5, 128.1, 127.3, 127.0, 126.3, 91.2, 63.1, 54.5, 48.6, 45.9, 29.9, 28.3, 21.3; m/z (ESI-MS) 323.1 [M + H]+.

Product 6o

Following general procedure A, product 6o was obtained in 41% yield.

Characterization data for 6o:

yellowish solid; mp 120–124 °C; R = 0.26 in 30% EtOAc/Hex; [α]D25 −31.3 (c 0.5, CHCl3); IR (KBr) 3063, 3031, 2999, 2927, 2860, 2833, 1610, 1546, 1514, 1452, 1366, 1306, 1249, 1175, 1143, 1101, 1035, 827, 731 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.22–7.17 (m, 1H), 7.17–7.10 (comp, 3H), 7.06 (app t, J = 7.5 Hz, 1H), 6.89–6.80 (comp, 3H), 4.88 (dd, J = 11.2, 9.7 Hz, 1H), 4.34 (d, J = 9.7 Hz, 1H), 3.77 (s, 3H), 3.54–3.45 (m, 1H), 3.34–3.18 (comp, 3H), 3.05 (ddd, J = 15.7, 9.3, 6.3 Hz, 1H), 2.96 (app dt, J = 16.4, 4.1 Hz, 1H), 2.92–2.85 (m, 1H), 2.09 (ddd, J = 15.0, 12.8, 4.7 Hz, 1H), 1.80–1.74 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 159.2, 134.2, 133.0, 132.0, 129.5, 128.5, 128.1, 127.0, 126.3, 114.5, 91.4, 63.1, 55.4, 54.5, 48.2, 45.9, 29.8, 28.3; m/z (ESI-MS) 339.2 [M + H]+.

Product 6p

Following general procedure A, product 6p was obtained in 60% yield.

Characterization data for 6p:

Yellowish solid; mp > 190 °C; R = 0.45 in 30% EtOAc/Hex; [α]D25 −12.5 (c 0.5, CHCl3); IR (KBr) 3055, 3017, 2927, 2855, 2810, 1600, 1537, 1496, 1440, 1357, 1309, 1140, 1102, 1063, 939, 856, 745 cm–1; 1H NMR (500 MHz, CD2Cl2) δ 7.86–7.85 (comp, 3H), 7.71 (s, 1H), 7.56–7.45 (comp, 2H), 7.40 (app d, J = 8.4 Hz, 1H), 7.26–7.22 (comp, 2H), 7.09 (app t, J = 6.2 Hz, 1H), 6.86 (app d, J = 7.8 Hz, 1H), 5.11 (app t, J = 9.6 Hz, 1H), 4.43 (d, J = 9.6 Hz, 1H), 3.75 (app td, J = 12.4, 4.3 Hz, 1H), 3.41 (app td, J = 11.2, 4.6 Hz, 1H), 3.38–3.33 (m, 1H), 3.29 (dd, J = 13.0, 3.2 Hz, 1H), 3.15–2.99 (comp, 2H), 2.99–2.88 (m, 1H), 2.29–2.21 (m, 1H), 1.87–1.85 (m, 1H); 13C NMR (125 MHz, CD2Cl2) δ 137.6, 134.8, 133.7, 133.3, 133.0, 129.6, 128.9, 128.0, 127.9, 127.8, 126.9, 126.5(8), 126.5(5), 126.2, 126.0, 125.1, 91.0, 63.1, 54.3, 49.1, 45.7, 29.8, 28.0; m/z (ESI-MS) 359.2 [M + H]+.

Product 6q

Following general procedure A, product 6q was obtained in 50% yield.

Characterization data for 6q:

yellowish solid; mp 128–130 °C; R = 0.35 in 30% EtOAc/Hex; [α]D25 −35.2 (c 0.5, CHCl3); IR (KBr) 3118, 3062, 3021, 2952, 2921, 2858, 1548, 1496, 1454, 1361, 1309, 1146, 1102, 1081, 1012, 932, 742 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.35–7.30 (m, 1H), 7.22–7.17 (m, 1H), 7.16–7.12 (m, 1H), 7.07 (app t, J = 7.5 Hz, 1H), 6.84 (app d, J = 7.8 Hz, 1H), 6.26 (dd, J = 3.3, 1.9 Hz, 1H), 6.11 (app d, J = 3.3 Hz, 1H), 4.92 (app t, J = 9.8 Hz, 1H), 4.32 (d, J = 9.8 Hz, 1H), 3.74 (app td, J = 12.6, 4.4 Hz, 1H), 3.36–3.17 (comp, 3H), 3.05 (ddd, J = 16.3, 9.9, 6.5 Hz, 1H), 2.93 (app dt, J = 16.4, 3.6 Hz, 1H), 2.86 (ddd, J = 11.3, 6.4, 2.9 Hz, 1H), 2.22–2.14 (m, 1H), 1.90–1.83 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 152.9, 142.5, 134.1, 132.7, 129.5, 128.2, 127.0, 126.2, 110.5, 106.7, 88.9, 62.7, 53.8, 45.4, 41.8, 29.7, 24.8; m/z (ESI-MS) 299.2 [M + H]+.

Product 6r

Following general procedure A, product 6r was obtained in 44% yield.

Characterization data for 6r:

yellowish solid; mp 150–152 °C; R = 0.29 in 30% EtOAc/Hex; [α]D25 −35.1 (c 0.5, CHCl3); IR (KBr) 3062, 3024, 2997, 2927, 2858, 2834, 1610, 1541, 1506, 1454, 1364, 1306, 1271, 1250, 1143, 1032, 763, 693 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.32–7.29 (comp, 2H), 7.25 (d, J = 7.1 Hz, 1H), 7.24–7.20 (comp, 2H), 6.79 (d, J = 8.6 Hz, 1H), 6.68 (d, J = 2.3 Hz, 1H), 6.63 (dd, J = 8.6, 2.6 Hz, 1H), 4.92 (dd, J = 11.1, 9.7 Hz, 1H), 4.31 (d, J = 9.7 Hz, 1H), 3.76 (s, 3H), 3.54 (app td, J = 12.6, 4.3 Hz, 1H), 3.33–3.25 (comp, 2H), 3.23 (ddd, J = 13.7, 4.5, 1.8 Hz, 1H), 3.03 (ddd, J = 15.7, 9.2, 6.3 Hz, 1H), 2.94 (app dt, J = 15.7, 4.0 Hz, 1H), 2.89–2.85 (m, 1H), 2.15–2.06 (m, 1H), 1.84–1.74 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 159.2, 140.0, 135.7, 129.2, 128.1, 127.9, 127.5, 125.4, 114.4, 112.1, 91.3, 62.8, 55.4, 54.5, 48.9, 45.9, 30.2, 28.3; m/z (ESI-MS) 339.1 [M + H]+.

Product 6s

Following general procedure A, product 6s was obtained in 52% yield.

Characterization data for 6s:

yellowish solid; mp 148–151 °C; R = 0.42 in 50% EtOAc/Hex; [α]D25 −18.9 (c 0.5, CHCl3); IR (KBr) 3059, 3028, 2990, 2945, 2921, 2889, 2883, 2855, 2834, 1610, 1544, 1520, 1447, 1354, 1261, 1226, 1143, 1112, 1019, 873, 759, 704 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.30–7.28 (comp, 2H), 7.25–7.22 (m, 1H), 7.22–7.18 (comp, 2H), 6.61 (s, 1H), 6.37 (s, 1H), 4.89 (dd, J = 11.2, 9.6 Hz, 1H), 4.27 (d, J = 9.6 Hz, 1H), 3.83 (s, 3H), 3.72 (s, 3H), 3.51 (app td, J = 12.7, 4.3 Hz, 1H), 3.30–3.18 (comp, 3H), 2.99–2.91 (m, 1H), 2.89–2.83 (comp, 2H), 2.10 (ddd, J = 15.1, 12.7, 4.8 Hz, 1H), 1.78 (app ddt, J = 13.7, 4.3, 2.4 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 148.7, 147.3, 139.8, 129.1, 128.0, 127.4, 126.6, 125.1, 111.8, 109.8, 91.7, 63.0, 56.0(1), 55.9(9), 54.5, 49.0, 46.2, 29.5, 28.2; m/z (ESI-MS) 369.1 [M + H]+.

Product 6t

Following general procedure A, product 6t was obtained in 37% yield.

Characterization data for 6t:

yellowish solid; mp 144–146 °C; (R = 0.31 in 30% EtOAc/Hex); [α]D25 −38.5 (c 0.5, CHCl3); IR (KBr) 3409, 3056, 3031, 2947, 2917, 2846, 2806, 2757, 1729, 1598, 1546, 1492, 1455, 1356, 1311, 1264, 1168, 738, 701 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.65 (br s, 1H), 7.55–7.50 (m, 1H), 7.39–7.33 (comp, 2H), 7.33–7.29 (m, 1H), 7.27–7.21 (comp, 3H), 7.17 (app td, J = 7.6, 1.3 Hz, 1H), 7.14–7.10 (m, 1H), 4.88 (dd, J = 11.2, 9.5 Hz, 1H), 4.25 (d, J = 9.5 Hz, 1H), 3.44–3.33 (m, 1H), 3.25–3.18 (comp, 2H), 3.05–2.93 (comp, 2H), 2.92–2.78 (comp, 2H), 2.21–2.13 (m, 1H), 1.99 (app ddt, J = 13.6, 4.7, 2.5 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 139.1, 136.8, 130.2, 129.3, 128.3, 127.5, 126.7, 122.7, 120.0, 118.5, 111.6, 111.2, 92.8, 61.9, 55.1, 51.3, 49.7, 31.5, 22.1; m/z (ESI-MS) 348.2 [M + H]+.

Products 8a and 9a

Following general procedure B, products 8a and 9a were obtained in a 1.2:1 ratio (62% combined yield). The relative stereochemistry was determined by GCOSY and NOESY NMR.

Characterization data for 8a:

yellowish oil; R = 0.37 in 20% EtOAc/Hex; [α]D25 +24.8 (c 0.5, CHCl3); IR (KBr) 3066, 3031, 2977, 2895, 2816, 2776, 2757, 2678, 1546, 1494, 1452, 1375, 1289, 1151, 1119, 1072, 1039, 751, 696 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.36–7.30 (comp, 2H), 7.29–7.27 (m, 1H), 7.21–7.12 (comp, 4H), 7.08–7.03 (comp, 2H), 4.66 (dd, J = 11.1, 8.2 Hz, 1H), 4.03 (d, J = 15.2 Hz, 1H), 3.56 (d, J = 15.2 Hz, 1H), 3.19 (dd, J = 18.5, 10.4 HZ, 1H), 3.01–2.92 (comp, 2H), 2.93–2.85 (m, 1H), 2.84–2.77 (m, 1H), 2.26–2.13 (comp, 2H), 0.78 (d, J = 6.1 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 137.6, 132.9, 131.3, 129.0, 128.2, 127.9, 126.8, 126.3, 125.8, 96.2, 62.8, 60.6, 57.4, 54.0, 34.3, 32.8, 16.9; HRMS (ESI) m/z calcd for C20H23N2O2 [M + H]+ 323.1754, found 323.1765.

Characterization data for 9a:

yellowish solid; mp 182–185 °C; R = 0.48 in 20% EtOAc/Hex; [α]D25 −31.6 (c 0.5, CHCl3); IR (KBr) 3068, 3028, 2975, 2895, 2813, 2778, 2763, 1546, 1494, 1455, 1375, 1364, 1289, 1156, 1115, 1032, 750, 698 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.35–7.32 (comp, 2H), 7.28–7.23 (comp, 3H), 7.20–7.13 (comp, 2H), 7.12–7.02 (comp, 2H), 5.09 (dd, J = 12.3, 9.1 Hz, 1H), 3.96 (d, J = 15.1 Hz, 1H), (dd, J = 12.3, 4.5 Hz, 1H), 3.53 (d, J = 15.1 Hz, 1H), 3.16–3.02 (comp, 2H), 2.92–2.82 (comp, 2H), 2.70 (dd, J = 11.5, 3.2 Hz, 1H), 2.31–2.14 (m, 1H), 1.00 (d, J = 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 138.1, 133.2, 131.5, 128.6, 128.2, 127.7, 127.5, 126.7, 126.2, 125.8, 89.7, 62.0, 61.7, 57.8, 49.8, 35.0, 33.1, 13.3; m/z (ESI-MS) 323.2 [M + H]+.

Products 8c and 9c

Following general procedure B, products 8c and 9c were obtained in a 1.2:1 ratio (49% combined yield).

Characterization data for 8c:

yellow solid; mp 180–182 °C; R = 0.31 in 20% EtOAc/Hex; [α]D25 +36.7 (c 0.5, CHCl3); IR (KBr) 3068, 3026, 2962, 2930, 2883, 1971, 1929, 1897, 1714, 1650, 1546, 1489, 1452, 1375, 1262, 1153, 1007, 815, 758, 738 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.49–7.43 (comp, 2H), 7.20–7.12 (comp, 2H), 7.09–7.04 (comp, 4H), 4.59 (dd, J = 11.4, 8.4 Hz, 1H), 4.02 (d, J = 15.1 Hz, 1H), 3.55 (d, J = 15.1 Hz, 1H), 3.21–3.13 (m, 1H), 3.04–2.73 (comp, 4H), 2.24–2.06 (comp, 2H), 0.78 (d, J = 6.1 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 136.6, 132.7, 132.1, 131.1, 128.2, 126.7, 126.3, 125.8, 121.8, 95.9, 62.6, 60.5, 57.2, 53.4, 34.2, 32.7, 16.7; m/z (ESI-MS) (79Br) 401.1 [M + H]+, (81Br) 403.1 [M + H]+.

Characterization data for 9c:

yellow solid; mp >200 °C; R = 0.53 in 20% EtOAc/Hex; [α]D25 −32.2 (c 0.5, CHCl3); IR (KBr) 3066, 3025, 2964, 2928, 2896, 2811, 2762, 1892, 1730, 1652, 1546, 1489, 1456, 1377, 1363, 1306, 1287, 1257, 1153, 1108, 1073, 1009, 825, 800, 749 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.51–7.44 (comp, 2H), 7.20–7.14 (comp, 2H), 7.14–7.03 (comp, 4H), 5.02 (dd, J = 12.3, 8.9 Hz, 1H), 3.96 (d, J = 15.1 Hz, 1H), 3.61 (dd, J = 12.3, 4.5 Hz, 1H), 3.52 (d, J = 15.1 Hz, 1H), 3.12–3.01 (comp, 2H), 2.94–2.80 (comp, 2H), 2.68 (dd, J = 11.6, 3.2 Hz, 1H), 2.24–2.13 (m, 1H), 0.98 (d, J = 7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 137.1, 133.1, 131.8, 131.4, 129.4, 128.2, 126.7, 126.3, 125.8, 121.5, 89.5, 61.8, 61.6, 57.7, 49.3, 34.8, 33.1, 13.2; m/z (ESI-MS) (79Br) 401.2 [M + H]+, (81Br) 403.2 [M + H]+.

Products 8e and 9e

Following general procedure B, products 8e and 9e were obtained in a 1.3:1 ratio (54% combined yield).

Characterization data for 8e:

yellow solid; mp 115–117 °C; R = 0.28 in 20% EtOAc/Hex; [α]D25 +25.1 (c 0.5, CHCl3); IR (KBr) 3024, 2965, 2928, 2894, 2821, 2762, 2680, 1959, 1902, 1796, 1593, 1545, 1495, 1373, 1362, 1255, 1093, 1011, 933, 818, 745 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.18–7.13 (comp, 2H), 7.12–7.07 (comp, 2H), 7.09–7.02 (comp, 2H), 6.88–6.84 (comp, 2H), 4.59 (dd, J = 11.4, 8.7 Hz, 1H), 4.01 (d, J = 15.2 Hz, 1H), 3.78 (s, 3H), 3.54 (d, J = 15.2 Hz, 1H), 3.23–3.13 (m, 1H), 2.99–2.88 (comp, 2H), 2.96–2.80 (comp, 2H), 2.22–2.10 (comp, 2H), 0.78 (d, J = 6.2 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 159.3, 133.1, 131.5, 129.7, 128.5, 127.0, 126.5, 126.1, 114.5, 96.7, 63.1, 60.8, 57.6, 55.4, 53.5, 34.6, 33.1, 17.1; m/z (ESI-MS) 353.2 [M + H]+.

Characterization data for 9e:

yellow solid; mp >200 °C; (R = 0.45 in 20% EtOAc/Hex); [α]D25 −31.6 (c 0.5, CHCl3); IR (KBr) 3026, 3013, 2992, 2969, 2955, 2899, 2835, 2780, 2761, 1966, 1922, 1884, 1613, 1548, 1512, 1456, 1442, 1399, 1380, 1355, 1310, 1300, 1254, 1178, 1028, 829, 748 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.19–7.13 (comp, 4H), 7.11–7.06 (m, 1H), 7.06–7.02 (m, 1H), 6.89–6.85 (comp 2H), 5.03 (dd, J = 12.3, 9.2 Hz, 1H), 3.95 (d, J = 15.1 Hz, 1H), 3.79 (s, 3H), 3.58 (dd, J = 12.3, 4.5 Hz, 1H), 3.52 (d, J = 15.1 Hz, 1H), 3.12–3.00 (comp, 2H), 2.93–2.79 (comp, 2H), 2.68 (dd, J = 11.5, 3.2 Hz, 1H), 2.21–2.13 (m, 1H), 1.00 (d, J = 7.2 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 159.1, 133.4, 131.7, 130.3, 129.0, 128.4, 126.9, 126.4, 126.0, 114.3, 90.2, 62.2, 61.9, 58.0, 55.5, 49.3, 35.3, 33.4, 13.6; m/z (ESI-MS) 353.2 [M + H]+.

Product 8k

Following general procedure B, product 8k was obtained in 48% yield. The relative stereochemistry was determined by GCOSY and NOESY NMR.

Characterization data for 8k:

yellow solid; mp 160–163 °C; R = 0.47 in 30% EtOAc/Hex; [α]D25 +27.2 (c 0.5, CHCl3); IR (KBr) 3061, 3026, 2932, 2865, 2799, 2749, 1721, 1650, 1541, 1437, 1366, 1240, 1141, 1141, 738 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.37–7.30 (comp, 2H), 7.30–7.27 (m, 1H), 7.25–7.20 (comp, 2H), 7.19–7.13 (comp, 2H), 7.09–7.02 (comp, 2H), 4.62 (dd, J = 11.4, 8.6 Hz, 1H), 4.03 (d, J = 15.1 Hz, 1H), 3.58 (d, J = 15.1 Hz, 1H), 3.30 (app td, J = 11.8, 4.8 Hz, 1H), 3.23 (app dt, J = 11.8, 3.0 Hz, 1H), 3.02–2.91 (comp 2H), 2.89–2.78 (m, 1H), 2.49 (app td, J = 11.8, 3.6 Hz, 1H), 2.16–1.95 (comp, 2H); 13C NMR (75 MHz, CDCl3) δ 139.2, 132.9, 131.3, 129.0, 128.2, 128.0, 127.2, 126.8, 126.3, 125.8, 95.7, 60.6, 57.5, 55.1, 47.2, 32.9, 30.9; m/z (ESI-MS) 309.1 [M + H]+.

Product 8l

Following general procedure B, product 8l was obtained in 43% yield.

Characterization data for 8l:

yellow solid; mp 165–167 °C; R = 0.48 in 30% EtOAc/Hex; [α]D25 +18.2 (c 0.5, CHCl3); IR (KBr) 3042, 2965, 2928, 2894, 2821, 2762, 2680, 1959, 1902, 1796, 1593, 1543, 1495, 1373, 1362, 1351, 1255, 1093, 1085, 1011, 933, 818, 745 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.34–7.29 (comp, 2H), 7.18–7.13 (comp, 4H), 7.10–7.04 (comp, 2H), 4.56 (dd, J = 11.3, 8.6 Hz, 1H), 4.03 (d, J = 15.2 Hz, 1H), 3.58 (d, J = 15.2 Hz, 1H), 3.29 (app td, J = 11.4, 5.5 Hz, 1H), 3.25–3.18 (m, 1H), 3.02–2.91 (comp, 2H), 2.87–2.79 (comp, 2H), 2.47 (app td, J = 11.6, 4.4 Hz, 1H), 2.10–1.99 (comp, 2H); 13C NMR (125 MHz, CDCl3) δ 137.6, 133.7, 132.8, 131.1, 129.2, 128.5, 128.1, 126.7, 126.2, 125.7, 95.4, 60.4, 57.3, 54.9, 46.5, 32.8, 30.7; m/z (ESI-MS) (35Cl) 343.2 [M + H]+, (37Cl) 345.2 [M + H]+.

Product 8n

Following general procedure B, product 8n was obtained in 61% yield.

Characterization data for 8n:

yellow solid; mp 175–178 °C; R = 0.51 in 30% EtOAc/Hex; [α]D25 +19.4 (c 0.5, CHCl3); IR (KBr) 3021, 2947, 2922, 2894, 2820, 2759, 2687, 2356, 1924, 1897, 1548, 1515, 1496, 1456, 1376, 1351, 1256, 1152, 811, 748 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.21–7.12 (comp, 6H), 7.11–7.05 (comp, 2H), 4.61 (dd, J = 11.4, 8.7 Hz, 1H), 4.04 (d, J = 15.2 Hz, 1H), 3.59 (d, J = 15.2 Hz, 1H), 3.29 (dd, J = 11.8, 4.7 Hz, 1H), 3.23 (app dt, J = 11.8, 3.2 Hz, 1H), 3.04–2.93 (comp, 2H), 2.86 (dd, J = 13.7, 7.0 Hz, 1H), 2.48 (app td, J = 11.8, 3.5 Hz, 1H), 2.34 (s, 3H), 2.15–1.99 (comp, 2H); 13C NMR (75 MHz, CDCl3) δ 137.6, 136.2, 132.9, 131.3, 129.7, 128.2, 127.0, 126.8, 126.3, 125.8, 95.8, 60.6, 57.5, 55.1, 46.8, 32.9, 30.9, 21.1; m/z (ESI-MS) 323.1[M + H]+.

Products 11 and 12

Following general procedure C, products 11 and 12 were obtained in a 2:1 ratio (55% combined yield). The relative stereochemistry was determined by GCOSY and NOESY NMR.

Characterization data for 11:

yellowish oil; R = 0.40 in 50% EtOAc/Hex; IR (KBr) 3056, 3033, 2932, 2851, 2804, 2754, 1529, 1489, 1452, 1368, 1306, 1143, 740 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.12 (app t, J = 7.4 Hz, 1H), 7.05 (app d, J = 7.5 Hz, 1H), 7.00 (app t, J = 7.5 Hz, 1H), 6.78 (app d, J = 7.5 Hz, 1H), 4.74–4.62 (m, 1H), 4.20 (d, J = 9.3 Hz, 1H), 3.15–3.07 (m, 1H), 3.04–2.93 (comp, 2H), 2.90–2.85 (comp, 2H), 2.75 (app dt, J = 11.1, 5.3 Hz, 1H), 2.30–2.23 (comp, 2H) 1.82–1.72 (m, 1H), 1.63–1.55 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 134.4, 133.3, 129.6, 127.9, 126.6, 126.3, 86.0, 62.6, 53.8, 46.6, 31.1, 29.3, 20.0; m/z (ESI-MS) 233.2 [M + H]+.

Characterization data for 12:

yellowish oil; R = 0.50 in 50% EtOAc/Hex; IR (KBr) 3061, 3026, 2932, 2865, 2799, 2749, 1721, 1650, 1541, 1437, 1366, 1240, 1141, 1141, 738 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.22–7.13 (comp, 3H), 7.12–7.09 (m, 1H), 5.18 (app dt, J = 4.5, 2.3 Hz, 1H), 3.68 (s, 1H), 3.16 (ddd, J = 16.9, 12.2, 5.3 Hz, 1H), 3.12–3.07 (m, 1H), 3.00 (ddd, J = 11.1, 5.3, 1.7 Hz, 1H), 2.69–2.60 (comp, 2H), 2.59–2.50 (m, 1H), 2.41 (app td, J = 12.0, 3.0 Hz, 1H), 2.26–2.15 (m, 1H), 1.94 (ddd, J = 18.5, 9.3, 4.9 Hz, 1H), 1.72–1.61 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 135.9, 133.8, 129.4, 126.8, 126.2, 124.4, 82.7, 65.6, 56.5, 52.7, 29.5, 28.9, 21.1; m/z (ESI-MS) 233.2 [M + H]+.

Product 13

Following general procedure B (5 equiv of 2-EHA was used), product 13 was obtained in 61% yield. The relative stereochemistry was determined by GCOSY and NOESY NMR.

Characterization data for 13:

yellowish solid; mp 75–77 °C; (R = 0.43 in 50% EtOAc/Hex); IR (KBr) 3066, 3028, 2950, 2820, 2754, 2687, 2361, 2329, 1964, 1919, 1842, 1805, 1546, 1496, 1463, 1455, 1357, 1347, 1277, 1237, 1218, 1117, 1105, 744 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.17–7.10 (comp, 2H), 7.08–6.99 (comp, 2H), 4.45–4.40 (m, 1H), 3.95 (d, J = 15.2 Hz, 1H), 3.53 (d, J = 15.2 Hz, 1H), 3.12–3.05 (m, 1H), 2.91–2.80 (comp, 3H), 2.40–2.32 (m, 1H), 2.27 (app td, J = 12.1, 2.8 Hz, 1H), 2.09–1.99 (m, 1H), 1.95–1.87 (m, 1H), 1.78 (ddd, J = 16.3, 8.4, 3.5 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 133.0, 131.5, 128.2, 126.6, 126.2, 125.8, 89.8, 59.9, 57.5, 54.7, 32.7, 30.1, 22.8; m/z (ESI-MS) 233.2 [M + H]+.

Product 15

Compound 8k was reduced following an adapted literature procedure.[32] To a stirred solution of 8k (0.09 mmol, 0.053 g) in i-PrOH (2 mL) was added 1 M HCl (1.8 mmol, 1.8 mL) followed by Zn dust (5.45 mmol, 0.356 g). The reaction mixture was stirred at room temperature for 2 h. The reaction was then quenched by addition of saturated NaHCO3 (aq). The resulting mixture was stirred vigorously for 20 min and then filtered through a plug of Celite and washed with EtOAc. The filtrate was extracted with EtOAc, and the combined organic layers were dried over Na2SO4, filtered, and evaporated under reduced pressure. The residue was purified by flash chromatography to give the title compound as a white solid in 83% yield.

Characterization data for 15:

mp 122–125 °C; R = 0.25 in 5% MeOH/EtOAc; [α]D25 +66.8 (c 0.5, CHCl3); IR (KBr); 3409, 3061, 3024, 2919, 2801, 2755, 1949, 1599, 1588, 1553, 1493, 1453, 1362, 1346, 1120, 1096, 1011, 863, 748 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.38–7.32 (comp, 2H), 7.30–7.24 (comp, 3H), 7.17–7.10 (comp, 3H), 7.07–7.02 (m, 1H), 3.95 (d, J = 15.2 Hz, 1H), 3.50 (d, J = 15.2 Hz, 1H), 3.31 (dd, J = 16.5, 4.4 Hz, 1H), 3.19 (app dt, J = 11.5, 3.3 Hz, 1H), 2.87–2.77 (comp, 2H), 2.49–2.41 (m, 1H), 2.38 (app td, J = 12.2, 2.8 Hz, 1H), 2.23 (app dq, J = 10.5 Hz, 4.3 Hz, 1H), 2.05 (app qd, J = 12.8, 3.7 Hz, 1H), 1.93–1.86 (m, 1H), 1.24 (br s, 2H); 13C NMR (125 MHz, CDCl3) δ 143.2, 133.6, 133.3, 128.8, 128.3, 127.8, 126.9, 126.4, 125.8, 125.7, 64.8, 59.6, 58.1, 55.8, 51.3, 34.0, 32.2; m/z (ESI-MS) 279.2 [M + H]+.

Product 16

Compound 6k was denitrated following an adapted literature procedure.[33] To a stirred solution of 6k (31 mg, 0.1 mmol, 94% ee) in EtOH (2 mL) was added Pd(OH)2/C (20 wt %, 75 mg). The reaction mixture was purged twice with hydrogen gas and then placed under 1 bar of hydrogen gas at 60 °C for 14 h. After being cooled to room temperature, the mixture was filtered through a Celite pad and washed with ethyl acetate. The solvent was removed under reduced pressure, and the crude material purified by flash chromatography to give the desired product as an off-white solid in 75% yield.

Characterization data for 16:

mp 124–127 °C; R = 0.41 in 40% EtOAc/Hex; [α]D25 −27.2 (c 0.5, CHCl3); IR (KBr) 3058, 3032, 2942, 2915, 2801, 2742, 1598, 1494, 1450, 1348, 1296, 1151, 1131, 1104, 1064, 1039, 963, 758, 733, 696 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.36–7.27 (comp, 4H), 7.25–7.18 (comp, 2H), 7.16–7.09 (comp, 3H), 3.32 (app d, J = 11.0 Hz, 1H), 3.23 (ddd, J = 17.0, 12.1, 6.1 Hz, 1H), 3.15 (app dt, J = 11.4, 3.1 Hz, 1H), 3.06 (dd, J = 11.4, 6.0 Hz, 1H), 2.87–2.72 (comp, 2H), 2.60 (app td, J = 11.6, 3.9 Hz, 1H), 2.54–2.49 (comp, 2H), 2.03–1.87 (comp, 2H), 1.70 (app q, J = 12.4 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 146.4, 138.1, 134.7, 129.2, 128.7, 127.2, 126.5, 126.3, 126.0, 125.0, 63.5, 57.1, 52.6, 43.7, 39.2, 33.3, 29.9; m/z (ESI-MS) 264.3 [M + H]+; HPLC Daicel Chiralcel OD-H, n-hexane/i-PrOH/diethylamine = 94.95/5/0.05, flow rate = 1 mL/min, UV = 254 nm, tR = 6.2 min (major) and tR = 22.1 min (minor), 94% ee.

Product 17

Alkylation of 11 was achieved following an adapted literature procedure.[34] To a stirred solution of 11 (0.1 mmol, 0.023 g) and methyl vinyl ketone (0.13 mmol, 0.01 mL) in MeCN (1 mL) was added DBU (0.1 mmol, 0.015 mL) at room temperature. The reaction mixture was stirred for 15 h at room temperature. Solvent was removed under reduced pressure, and the crude material purified by flash chromatography to give the title compound as a colorless oil in 69% yield.

Characterization data for 17

The relative stereochemistry was determined by GCOSY and NOESY NMR: R = 0.32 in 20% EtOAc/Hex; IR (KBr) 3073, 3021, 2962, 2900, 2814, 2759, 1719, 1645, 1521, 1450, 1358, 1299, 1252, 1141, 1106, 1052, 745 cm–1; 1H NMR (400 MHz, CDCl3) δ 7.19–7.11 (m, 1H), 7.08–7.03 (comp, 2H), 6.69 (app d, J = 7.9 Hz, 1H), 4.27 (s, 1H), 3.18–3.06 (m, 1H), 3.03–2.99 (m, 1H), 2.90 (app dd, J = 10.8, 3.0 Hz, 1H), 2.79–2.63 (comp, 2H), 2.59–2.45 (comp, 4H), 2.36–2.21 (m, 1H), 2.15–2.02 (comp, 4H), 1.95–1.87 (m, 1H), 1.80–1.61 (comp, 2H); 13C NMR (75 MHz, CDCl3) δ 207.6, 137.4, 132.1, 129.2, 127.0, 126.2, 125.6, 94.5, 69.7, 55.7, 51.1, 37.8, 34.7, 30.9, 30.0, 22.5, 22.4; m/z (ESI-MS) 303.2 [M + H]+.

Product 18

To a stirred solution of (E)-(((4-nitrobut-3-en-1-yl)oxy)methyl)benzene (0.858 g, 4.14 mmol, 1 equiv), (S)-diphenylprolinol trimethylsilyl ether (0.135 g, 0.414 mmol, 10 mol %), and p-nitrophenol (0.028 g, 0.207 mmol, 5 mol %) in toluene (4.14 mL) was added n-butyraldehyde (1.12 mL, 12.42 mmol, 3 equiv) at room temperature. The reaction mixture was stirred for 14 h and quenched by the addition of 1 M HCl (10 mL), and the resulting mixture was extracted with EtOAc (2 × 10 mL). The combined organic layers were dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography to give the title compound as a colorless oil in 73% yield (dr = 6.5:1).

Characterization data for 18 (major diastereomer):

colorless oil; R = 0.35 in 10% EtOAc/Hex; [α]D25 +3.76 (c 0.25, CHCl3); IR (KBr) 3032, 2967, 2876, 2735, 1722, 1555, 1496, 1454, 1382, 1204, 1100, 1027, 739, 698 cm–1; 1H NMR (500 MHz, CDCl3) δ 9.67 (d, J = 1.2 Hz, 1H), 7.38–7.28 (m, 5H), 4.62 (dd, J = 12.8, 6.6 Hz, 1H), 4.46–4.45 (comp, 2H), 4.42 (dd, J = 12.8, 6.5 Hz, 1H), 3.51 (t, J = 5.8 Hz, 2H), 2.90–2.84 (m, 1H), 2.49–2.40 (m, 1H), 1.86–1.62 (comp, 3H), 1.54–1.46 (m, 1H), 1.00 (t, J = 7.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 202.9, 137.8, 128.4, 127.7(4), 127.6(8), 76.9, 73.1, 67.4, 54.0, 34.5, 29.1, 18.5, 12.1; m/z (ESI-MS) 280.2 [M + H]+; HPLC Daicel Chiralcel OJ-H, n-hexane/i-PrOH = 90/10, flow rate =1 mL/min, UV = 230 nm, tR = 78.2 min (major) and tR = 96.4 min (minor), 99% ee.

Product 19

A solution of the amine (0.232 g, 1.2 mmol, 2 equiv) and AcOH (0.346 mL, 6 mmol, 10 equiv) in toluene (6 mL) was heated under reflux. 4-Nitrobutyraldehyde 18 (0.167 g, 0.6 mmol, 0.12 M solution in toluene) was delivered through the top of the reflux condenser over 15 h via syringe pump. The reaction was then kept under reflux for a further 0.5–1 h at which time the aldehyde was consumed as judged by TLC analysis. Subsequently, the reaction mixture was allowed to cool to room temperature, diluted with EtOAc (20 mL), and washed with saturated aqueous NaHCO3 (3 × 20 mL). The combined aqueous layers were extracted with EtOAc (2 × 10 mL), and the combined organic layers were dried over anhydrous Na2SO4. Solvent was removed under reduced pressure and the residue purified by silica gel chromatography. Products 19, 19′, and 19″ were obtained in a 2:2:1 ratio, 61% combined yield.

Characterization Data for 19 (1S,2R,3R,11bR)-2-(2-(Benzyloxy)ethyl)-3-ethyl-9,10-dimethoxy-1-nitro-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinoline)

The relative stereochemistry was determined by GCOSY and NOESY NMR: brown oil; R = 0.45 in 50% EtOAc/Hex; [α]D25 −16.4 (c 0.25, CHCl3); IR (KBr) 3061, 2959, 2865, 2831, 1741, 1682, 1631, 1539, 1519, 1467, 1356, 1262, 1225, 1143, 1111, 740 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.38–7.19 (comp, 5H), 6.58 (s, 1H), 6.34 (s, 1H), 4.88–4.77 (m, 1H), 4.47 (d, J = 12.0 Hz, 1H), 4.43 (d, J = 12.0 Hz, 1H), 4.09 (d, J = 9.8 Hz, 1H), 3.83 (s, 3H), 3.76 (s, 3H), 3.48 (t, J = 6.6 Hz, 2H), 3.13 (dd, J = 13.5, 4.0 Hz, 1H), 3.02–2.97 (m, 1H), 2.92–2.85 (m, 1H), 2.81–2.62 (comp, 3H), 2.25–2.18 (m, 1H), 1.89–1.82 (m, 1H), 1.80–1.58 (comp, 3H), 1.23–1.09 (m, 1H), 0.90 (t, J = 7.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 148.7, 147.2, 138.4, 128.6, 127.7(7), 127.7(5), 126.4, 125.4, 111.8, 109.8, 91.2, 73.3, 67.0, 62.8, 59.0, 56.1, 56.0, 46.1, 43.6, 33.8, 29.4, 28.2, 23.3, 11.0; m/z (ESI-MS) 455.1 [M + H]+.

Characterization Data for 19′ ((1S,2R,3S,11bR)-2-(2-(Benzyloxy)ethyl)-3-ethyl-9,10-dimethoxy-1-nitro-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinoline)

The relative stereochemistry was determined by GCOSY and NOESY NMR: brown oil; R = 0.42 in 20% EtOAc/Hex; [α]D25 −69.9 (c 0.25, CHCl3); IR (KBr) 3026, 3009, 2937, 2865, 2806, 1726, 1608, 1551, 1462, 1363, 1269, 1225, 1096,1010, 876, 743, 698 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.38–7.26 (comp, 5H), 6.56 (s, 1H), 6.41 (s, 1H), 4.52 (d, J = 11.9 Hz, 1H), 4.44 (d, J = 11.9 Hz, 1H), 4.39–4.30 (m, 1H), 4.01 (d, J = 8.9 Hz, 1H), 3.83 (s, 3H), 3.75 (s, 3H), 3.50–3.43 (comp, 2H), 3.00–2.94 (comp, 2H), 2.88 (ddd, J = 11.0, 4.9, 3.0 Hz, 1H), 2.79–2.68 (comp, 2H), 2.59–2,54 (comp, 2H), 1.74–1.53 (comp, 4H), 1.52–1.42 (m, 1H), 1.42–1.31 (m, 1H), 0.88 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 148.1, 147.4, 138.4, 128.6, 128.4, 127.9(2), 127.8(5), 125.8, 111.8, 108.8, 92.4, 73.1, 67.0, 65.0, 57.0, 56.0, 51.3, 42.7, 37.2, 30.4, 28.2, 18.9, 12.5; m/z (ESI-MS) 455.1 [M + H]+.

Characterization data for 19″ (1R,2R,3S,11bS)-2-(2-(benzyloxy)ethyl)-3-ethyl-9,10-dimethoxy-1-nitro-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinoline):

brown oil; R = 0.55 in 50% EtOAc/Hex; [α]D25 +49.4 (c 0.25, CHCl3); IR (KBr) 3063, 3033, 2959, 2932, 2860, 2801, 2754, 1734, 1615, 1541, 1519, 1363, 1264, 1104, 740, 696 cm–1; 1H NMR (500 MHz, CDCl3) δ 7.40–7.26 (comp, 5H), 6.56 (s, 1H), 6.50 (s, 1H), 5.53 (app t, J = 2.1 Hz, 1H), 4.62 (d, J = 12.0 Hz, 1H), 4.56 (d, J = 12.0 Hz, 1H), 3.83 (s, 3H), 3.80 (s, 1H), 3.80–3.73 (m, 1H), 3.72–3.67 (m, 1H), 3.55 (s, 3H), 3.20–3.07 (m, 1H), 3.07–2.95 (m, 1H), 2.86 (dd, J = 10.8, 3.0 Hz, 1H), 2.81–2.70 (m, 1H), 2.59–2.46 (comp, 2H), 2.39–2.19 (comp, 2H), 1.92–1.74 (comp, 2H), 1.35–1.23 (comp, 2H), 0.94 (t, J = 7.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 147.6, 147.2, 137.8, 128.5, 127.9, 127.8, 127.5, 125.5, 111.6, 107.2, 86.0, 73.5, 70.1, 59.8, 56.9, 55.8, 55.7, 52.7, 39.8, 36.3, 28.9, 25.1, 23.1, 11.5; m/z (ESI-MS) 455.1 [M + H]+.

(−)-Protoemetinol

To a stirred solution of starting material 19 (91 mg, 0.2 mmol) in EtOH (4 mL) was added Pd(OH)2/C (20 wt %, 112 mg). The reaction mixture was purged twice with hydrogen gas and then placed under 1 bar of hydrogen gas at 70 °C for 30 h. After being cooled to room temperature, the mixture was filtered through a Celite pad and washed with ethyl acetate. The solvent was removed under reduced pressure and the crude material purified by flash chromatography to give the desired product as a yellow oil in 64% yield. (−)-Protoemetinol was previously reported, and its published characterization data matched our own in all respects.[2g,2l]

Characterization data for (−)-protoemetinol:

yellow oil; R = 0.45 in 30% MeOH/EtOAc; [α]D25 −46.5 (c 0.6, CHCl3); IR (KBr) 3422, 2956, 2931, 2874, 2868, 2751, 1610, 1510, 1463, 1365, 1330, 1253, 1230, 1148, 1100, 1040, 1000, 867, 767, 732; 1H NMR (500 MHz, CDCl3) δ 6.67 (s, 1H), 6.56 (s, 1H), 3.84 (s, 3H), 3.83 (s, 3H), 3.79–3.69 (comp, 2H), 3.14–3.00 (comp, 3H), 2.99–2.93 (m, 1H), 2.61 (app d, J = 15.9 Hz, 1H), 2.47 (app td, J = 11.5, 3.9 Hz, 1H), 2.33 (app d, J = 12.8 Hz, 1H), 2.05–1.97 (m, 1H), 1.93 (app dt, J = 11.1, 7.8 Hz, 1H), 1.70–1.63 (m, 1H), 1.49–1.36 (comp, 3H), 1.28–1.18 (m, 1H), 1.16–1.06 (m, 1H), 0.91 (t, J = 7.5 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 147.4, 147.1, 130.0, 126.7, 111.5, 108.3, 62.7, 61.4, 60.6, 56.1, 55.8, 52.5, 41.3, 37.6, 37.3, 35.9, 29.1, 23.5, 11.1; HRMS (ESI) m/z calcd for C19H30NO3 [M + H]+ 320.2220, found 320.2225.