Scope and Limitations of Xanthate-Mediated Synthesis of Functional γ-Thiolactones.

A modular platform based on free-radical xanthate addition to alkenes enables access to a large series of functional γ-thiolactones. This methodology includes two different pathways based on xanthate chemistry involving radical addition and Chugaev elimination steps. The first method uses the addition of an ester-functionalized xanthate to various commercially functional alkenes, whereas the second one is based on the addition of functional xanthates to an ester-functionalized alkene. In both cases, a series of xanthate/alkene monoadducts was obtained, and their thermolysis and subsequent cyclization led to a library of functional γ-thiolactones in moderate to good yield. For a few cases where it may not be possible to directly incorporate some targeted functional groups via the proposed process involving free radicals and high temperature, a bromo-functionalized thiolactone was used as a starting material for chemical transformations.

Introduction

In contrast with lactone monomers, which are widely used for the synthesis of polyesters via ring-opening polymerization (ROP),[1−3] thiolactones have barely been studied in ROP, with only a few attempts being made in both homo-[4−6] and copolymerization with other cyclic monomers.[7−9] Over the last decade, five-membered ring thiolactones (γ-thiolactones) have received renewed interest with the work of Du Prez et al. in the field of functional polymer synthesis. They highlighted that amines could readily open γ-thiolactones to generate a thiol that could be further reacted with a reactive double bond in a one-pot procedure.[10,11] The use of various functionalized homocysteine thiolactones for this so-called amine–thiol–ene conjugation reaction has led to the synthesis of a tremendous amount of complex functional polymers,[11,12] some exhibiting sequence-controlled structures.[13−17] Although this new reaction in polymer synthesis seems really promising, the modified homocysteine thiolactones available show a relatively limited structural diversity, with the amine group as the only possible substitution site.[11] Substitute groups can be introduced using acid halides,[18,19] carboxylic acids,[20] anhydrides,[21] or a xanthate approach[22] for example. Furthermore, only a few synthetic procedures give access to γ-thiolactones with limited functionalities, mainly through alkylation of thiolactones,[23] oxygen–sulfur exchange on γ-butyrolactone,[24,25] isomerization of thionolactone,[26] or acyl thiol–ene cyclization.[27]

In a 1998 paper, Zard et al. reported the first example of thiolactone synthesis using xanthate radical chemistry. The proposed methodology involved the use of an amine nucleophile and a strong acid catalyst in order to convert the xanthate into a thiolactone.[28]

Recently, we came up with a simpler and more versatile synthetic route to access various original thiolactones based on xanthate chemistry.[29] The procedure consists in the radical addition of a xanthate to a functional unsaturated compound, followed by an additive-free step involving a thermolysis reaction and subsequent cyclization, leading to a functional γ-thiolactone. Using a series of alkenes for the proof-of-concept study, we were able to access different thiolactones and successfully used them to create new functional polymers.[29] In this report, we present the scope and limitations of this xanthate-mediated synthesis of thiolactones through two different synthetic pathways (Scheme ).

Scheme 1

General Scheme of Two Different Pathways for the Synthesis of Functional Thiolactones Using Xanthate Chemistry

Results and Discussion

In a recent work, we described a synthetic procedure involving the radical addition of an O-alkyl xanthate to a substituted alkene, followed by the thermolysis of the resulting monoadduct to form a transient thiol that reacts with an ester group present on the starting xanthate to obtain the expected γ-thiolactone. The versatility of the method was exemplified with a first series of functional alkenes[29] (Scheme , M1–9 and TL1–9), but it needed to be further tested with more complex and reactive functional groups in order to estimate its full potential.

Scheme 2

(A) General Procedure for the Synthesis of Functional γ-Thiolactones Using Pathway 1 and Resulting (B) Xanthate/Alkene 1:1 Adducts and (C) Thiolactones

We selected a series of alkenes of different lengths bearing ether, bromide, hydroxyl, epoxide, pinacol boronate, and coumarin groups and tested them in conditions established previously for xanthate addition and thermolysis/cyclization steps.

The addition of XA1 to n-butyl vinyl and allyl ethers formed the expected monoadducts M10 and M11 in good yield. The thermolysis of M10 at 190 °C did not result in the formation of the corresponding thiolactone. 1H NMR analysis of the crude mixture showed the total decomposition of the xanthate group into the expected thiol. However, no cyclization occurred even after a prolonged reaction time at 190 °C. Thermolysis of M11 however led to the formation of thiolactone TL11 after 16 h with a good yield of 89% (Scheme ). It seems that the presence of an oxygen atom on the carbon bearing the thiol group inhibits the thioesterification reaction. Therefore, a spacer of at least one carbon atom is required to access γ-thiolactones bearing an ether functional group.

We then tested four bromoalkenes of different lengths with a view to prepare a range of bromo-functional thiolactones (Scheme ). Among allyl bromide, 4-bromo-1-butene, 5-bromo-1-pentene and 11-bromo-1-undecene reactants, only one thiolactone was successfully obtained with 11-bromo-1-undecene. In the case of allyl bromide and 4-bromo-1-butene, no reaction occurred between xanthate XA1 and the alkene. By increasing the distance between the bromide and the double bond with the use of 5-bromo-1-pentene, we obtained the expected monoadduct M12 by radical addition of XA1 to the alkene with a moderate yield of 49%. Unfortunately, the thermolysis of M12 did not lead to the formation of a thiolactone but a tetrahydrothiophene derivative (THT1, Scheme ) was revealed instead by NMR analysis (Figure S37). The thiol formed after the thermolysis of M12 did not perform the expected thiolactonization, but an intramolecular nucleophilic substitution on the bromine to form a stable tetrahydrothiophene was favored. To avoid this side reaction, we used 11-bromo-1-undecene instead. The radical addition of XA1 to the bromoalkene occurred with a good yield of 80% to form monoadduct M13. Thermolysis of M13 allowed this time the formation of thiolactone TL13 with a yield of 52% (Schemes and ). Our experimental procedure is therefore suitable for the synthesis of bromo-functionalized thiolactones, but the choice of the bromoalkene, especially the distance between the bromide and the double bond, is crucial for both radical addition and thiolactonization.

Scheme 3

Attempted Strategies for the Preparation of Brominated Thiolactones from Bromoalkene Precursors

Conditions for monoadduct formation: xanthate/alkene = 1:1, lauroyl peroxide (LPO), toluene, 90 °C, 16 h.

We recently reported the synthesis of a first hydroxy-functional γ-thiolactone using our xanthate-mediated method.[30]TL15 was obtained from 10-undecen-1-ol and proved its usefulness as a platform for the introduction of several new functions such as secondary and tertiary bromides, xanthates, and an alcoxyamine.[30] These thiolactones were then used as reversible-deactivation radical polymerization agents for atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization and nitroxide-mediated polymerization, and nitroxide-mediated polymerization for the synthesis of a diversity of thiolactone-terminated polymers of controlled chain length and narrow molar mass distribution.[30] We evaluated the possibility of shortening the length of the spacer between the hydroxyl group and the thiolactone ring. We selected allyl alcohol, 3-buten-1-ol, and 7-octene-1,2-diol to be reacted with either XA1 or XA2 or with both. The radical addition of XA1 to allyl alcohol did not lead to the formation of any product even after an extended period of time, as we observed with allyl bromide.

However, contrary to 4-bromo-1-butene that did not react at all, the addition of XA1 and XA2 to 3-buten-1-ol occurred and formed the corresponding monoadducts M15 and M16 with yields of 76 and 65%, respectively. The thermolysis of M15 and M16 led to the corresponding hydroxyl-functional thiolactones TL15 and TL16 with respective yields of 92 and 71% (Scheme ). Finally, a dihydroxy thiolactone was successfully synthesized by radical addition of XA1 to 7-octene-1,2-diol to form the monoadduct M17 with a moderate yield of 49%, followed by a thermolyzed to give the corresponding thiolactone TL17 with a good yield of 92% (Scheme ).

We challenged other functionalities of interest such as an epoxide, a methyl ester, a boronic ester, and a chromophore through the use of 1,2-epoxydecene, methyl 2-methyl-4-pentenoate, allyl pinacol boronate, and 4-(pent-4-en-1-hydroxy)2H-chromen-2-one. The radical addition of XA1 to 1,2-epoxydecene and allyl pinacol boronate ester gave the expected monoadducts M18 and M19 with similar yields of 75 and 74%, respectively (Scheme ). The heating up of M19 at 190 °C for 5 h led to the formation of the boronate pinacol ester-functionalized thiolactone with a yield of 68% (Scheme ). The thermolysis of M18 and cyclization of the resulting product at 190 °C required 7 h to reach a similar yield of 67% and the formation of the epoxide-functionalized thiolactone TL18 (Scheme ). The radical addition of XA1 to 4-(pent-4-en-1-hydroxy)2H-chromen-2-one occurred with a low yield of 37%, and the subsequent thermolysis of monoadduct M20 gave thiolactone TL20 with a yield of 57% (Scheme ).

The last functionality we introduced through this pathway was a methyl ester group. To do so, xanthate XA1 and methyl 2-methyl-4-pentenoate as the olefinic substrate were judiciously selected in order to obtain a symmetrical monoadduct M21 with a yield of 73%. Once the xanthate group was cleaved at 190 °C to form a thiol, two thiolactonization pathways became possible (Scheme ), with the thiol potentially reacting with either the methyl ester group of the xanthate or that brought by the alkene. It is worth mentioning that apart from this particular case, the thermolysis of a monoadduct bearing two different kinds of ester groups coming from the xanthate and the alkene would lead to mixtures of ester-functional thiolactones.

Scheme 4

Monoadduct M21 Leads to Thiolactone TL21 According to Two Distinct Mechanistic Pathways

The thermolysis of M21 at 190 °C required 48 h to form the expected thiolactone TL21 with a good yield of 89% (Scheme ).

The synthetic route to TL21 inspired us to develop a second pathway to access functional thiolactones using the same elemental reactions. Whereas the first methodology we proposed brought the functionality to the thiolactone through the functional alkene with thiolactone ring formation via the reaction of the thiol with the ester group from the initial xanthate, the newly proposed strategy involves the formation of the thiolactone ring through the reaction of the thiol and the ester group of the alkene, giving the possibility of introducing the thiolactone functionality from a functional xanthate (Scheme ).

Scheme 5

(A) General Procedure for the Synthesis of Thiolactones through Pathway 2 and (B) Resulting Xanthate/Alkene 1:1 Adducts and Thiolactones

We thus synthesized and screened four different xanthates to probe the limitations of this new process. We selected four different xanthates with benzyl (XA3), 1-phenylethyl (XA4), phthalimido (XA5), and cyanomethyl (XA6) leaving groups. The radical addition of both XA3 and XA4 to methyl 2-methyl-4-pentenoate failed to form the corresponding monoadduct. On the other hand, the addition of XA5 and XA6 to methyl 2-methyl-4-pentenoate occurred to afford monoadducts M22 with a moderate yield of 40% and M23 with a much better yield of 79% (Scheme ). Thiolactone TL22 could be obtained from the thermolysis of M22 for 24 h with an efficient thiolactonization proven by 1H NMR of the crude mixture but with a low isolated yield of 30% due to a loss of product during the purification step. Under the same conditions, M23 was converted into a mixture of the expected thiolactone TL23 and its trimer. The high temperature of 190 °C associated with an extended reaction time of 24 h led to the cyclotrimerization of the cyano group of the thiolactone in the neat reaction mixture. To avoid this side reaction, the experimental protocol was slightly modified, and the thermolysis was run on a diluted solution of M23 in dichlorobenzene at 190 °C for 24 h. This time, no cyclotrimer was obtained, and thiolactone TL23 was obtained with a 70% yield.

This alternative method of thiolactone synthesis (Scheme ) was found to be less versatile than the first one we developed. From the few tested xanthates, to date, only two thiolactones with functionalities of limited interest were obtained.

Although the xanthate-mediated synthesis of thiolactones is very versatile, some functional groups sensitive to radicals or high temperature may not be compatible with this synthetic procedure. To overcome this drawback and introduce new functionalities on the thiolactone ring, postfunctionalization of the thiolactone has to be considered (Scheme ). As mentioned earlier, we recently used this strategy to introduce bromides, xanthates, and an alkoxyamine functional group by an efficient transformation of the hydroxyl-functional thiolactone TL14.[30] Among the thiolactones synthesized, we considered bromo-functionalized thiolactone TL13 to be an interesting platform for the introduction of further functionalities.

Scheme 6

Synthesis of Functional Thiolactones via the Postfunctionalization of a Bromo-Functionalized Thiolactone

Nucleophilic substitution of TL13 with sodium azide, sodium ethanethiosulfonate, and the xanthate salt XAK led to the formation of an azide- (TL24), a thiosulfonate- (TL25), and a xanthate-functional thiolactone (TL26) with very good yields of, respectively, 86, 96, and 91% (Scheme ). Furthermore, TL27 bearing a xanthate functionality could be thermolyzed to give the corresponding thiol-functional thiolactone TL27 in 87% yield (Scheme ).

Conclusions

In summary, we report the synthesis of functional thiolactones through consecutive radical addition of xanthate to a functional alkene, high-temperature Chugaev elimination of the xanthate group, and ring closure of the resulting mercapto ester. Depending on the nature of the xanthate and the functional alkene, two different pathways give access to the target thiolactones, although only one was found to be truly versatile. The first pathway allows the introduction of a wide range of functionalities, with some limitations with reactive groups such as Br and OH that need to be borne by alkenes of a certain length to be able to obtain the desired thiolactone. A total of 18 γ-thiolactones was synthesized following this procedure. The second pathway involves the same elemental reactions but uses a functional xanthate in combination with an ester-functionalized alkene. This particular procedure requires the synthesis of a specific xanthate for each targeted thiolactone and the xanthates itself should add to the ester-functional alkene, which did not occur in several cases. To date, only two novel thiolactones bearing cyano and phthalimido groups could be synthesized according to this procedure. One particular case was found with the xanthate XA1–methyl 2-methyl-4-pentenoate pair, which leads to the formation of an ester-functional thiolactone according to both pathways 1 and 2 due to the symmetrical nature of the monoadduct (Scheme ). Finally, we used a bromo-functionalized thiolactone as a platform to introduce several functional groups we thought might be incompatible with free-radical conditions and elevated temperatures. As a whole, xanthate-mediated synthesis of γ-thiolactones was found to be a powerful synthetic tool allowing direct access to pure functional thiolactones on a several-gram scale, with also the possibility to be further functionalized. This ease of access to a new generation of highly reactive building blocks will undoubtedly open new application perspectives in the fields of polymer synthesis and modification and materials surface functionalization.

Experimental Section

General Procedures

Reactions were carried out in a Schlenk flask and heated using a dry bath. Column chromatography was carried out using silica gel (Sigma-Aldrich, 40–63 μm) packed in glass columns, and technical-grade solvents were used. The reported yields are isolated yields after purification.

Materials

Commercial reagents were purchased from Sigma-Aldrich, Alfa-Aesar, Acros Organics, or TCI and used as received. Xanthate salt XAK was prepared according the procedure described in the literature.[29] Methyl 2-methyl-4-pentenoate and 4-(pent-4-en-1-hydroxy)2H-chromen-2-one compounds were prepared following the procedures described next.

Instrumentation

NMR spectra (1H and 13C) were recorded at 25 °C in CDCl3 as solvent on a Bruker AVANCE 300 MHz instrument. 1H NMR spectra were recorded at 300.13 MHz, and coupling constants (J) are reported to ±0.5 Hz. The resonance multiplicities are described as s (singlet), d (doublet), t (triplet), q (quartet), or m (multiplet). 13C NMR spectra were recorded at 75.47 MHz. Chemical shifts δ are reported in parts per million (ppm) and are referenced to the residual solvent peak (CDCl3: H = 7.26 ppm and C = 77.16 ppm).

High-resolution mass spectra (HRMS) were recorded on a GCT 1er Waters spectrometer.

Procedure for the Synthesis of Methyl 2-Methyl-4-pentenoate

Ethyl 2-methyl-4-pentenoate (10 g, 70.4 mmol) was diluted in MeOH (120 mL), and H2SO4 (0.34 g, 3.5 mmol) was added. The solution was stirred at refluxing temperature for 24 h and then cooled down to room temperature. The reaction mixture was diluted with 120 mL of petroleum ether and washed with NaCl sat. solution (2 × 30 mL) and then with deionized water (3 × 30 mL). The organic phase was dried over anhydrous MgSO4, and the solvent was removed under reduced pressure. Methyl 2-methyl-4-pentenoate compound was obtained as a colorless liquid (7.15 g, 75%). 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.77–5.64 (m, 1H), 5.05–4.97 (m, 2H), 3.63 (s, 3H), 2.53–2.33 (m, 2H), 2.19–2.10 (m, 1H), 1.13–1.11 (dd, J = 6.9, 0.8 Hz, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 176.4, 135.4, 116.7, 51.4, 39.1, 37.7, 14.5.

Procedure for the Synthesis of 4-(Pent-4-en-1-hydroxy)2H-chromen-2-one

First, 4-hydroxycoumarin (0.91 g, 5.6 mmol) and K2CO3 (0.93 g, 6.7 mmol) were diluted in dimethylformamide (DMF, 10 mL) and stirred at 60 °C during 20 min. Then, 5-bromo-1-pentene (1 g, 6.7 mmol) was added dropwise, and the reaction was stirred during 2 h at room temperature. The mixture was extracted with dichloromethane (DCM, 80 mL) and washed with deionized water (3 × 50 mL). The organic phase was dried over anhydrous MgSO4, and the solvent was removed under pressure. Next, 4-(pent-4-en-1-hydroxy)2H-chromen-2-one compound was obtained as a white solid (1.01 g, 79%). 1H NMR (300 MHz, CDCl3) δ (ppm) = 7.81–7.24 (m, 4H), 5.98–5.83 (m, 1H), 5.68 (s, 1H), 5.14–5.05 (m, 2H), 4.18–4.13 (m, 2H), 2.35–2.28 (m, 2H), 2.08–2.01 (m, 2H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 165.6, 162.9, 153.3, 136.9, 132.4–123.0, 116.8, 115.9, 90.5, 68.5, 29.1–27.6.

Procedure for the Synthesis of Xanthates (XA1–6)

Xanthates XA1 and XA2 were prepared according to a procedure described in the literature.[29]

Benzyl bromide (for XA3) or (1-bromoethyl)benzene (for XA4) (5.0 g, 29 mmol) was added dropwise to a stirred solution of xanthate salt XAK (7.10 g, 35.1 mmol) in acetone (35 mL) at 0 °C. After stirring for 3 h, the mixture was filtered off to remove the formed KBr. The solvent was concentrated under reduced pressure to yield a yellow oil. XA3 (5.71 g, 77%) and XA4 (6.40 g, 93%) were used without additional purification.

S-Benzyl O-(3-Methylbutan-2-yl) Carbonodithioate (XA3)

1H NMR (300 MHz, CDCl3) δ (ppm) = 7.41–7.28 (m, 5H), 5.65–5.57 (m, 1H), 4.41–4.40 (s, 2H), 2.10–1.99 (m, 1H), 1.34–1.32 (d, J = 6.3 Hz, 3H), 1.01–0.98 (dd, J = 6.8, 1.5 Hz, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.7, 135.7, 129.8–127.6, 85.8, 40.2, 32.7, 18.2–17.9, 15.8.

O-(3-Methylbutan-2-yl) S-(1-Phenylethyl) Carbonodithioate (XA4)

1H NMR (300 MHz, CDCl3) δ (ppm) = 7.39–7.23 (m, 5H.), 5.58–5.50 (m, 1H), 4.94–4.86 (m, 1H), 2.03–1.90 (m, 1H), 1.72–1.69 (dd, J = 7.2, 1.8 Hz, 3H), 1.33–1.30 (d, J = 6.4 Hz, 1.5H), 1.21–1.18 (d, J = 6.4 Hz, 1.5H), 0.97–0.86 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.0, 141.8, 128.6–127.4, 85.4, 48.9, 32.6, 22.0, 18.4–17.9, 15.6.

S-((1,3-Dioxoisoindolin-2-yl)methyl) O-(3-Methylbutan-2-yl) Carbonodithioate (XA5)

N-(Bromoethyl)phtalimide (4.9 g, 21 mmol) was added portionwise to a stirred solution of xanthate salt XAK (4.0 g, 20 mmol) in acetone (35 mL) at 0 °C. After stirring for 3 h, the mixture was filtered off to remove the formed KBr. The solvent was concentrated under reduced pressure to yield a yellow oil (5.8 g, 91%). XA5 was used without additional purification. 1H NMR (300 MHz, CDCl3) δ (ppm) = 7.89–7.73 (m, 4H), 5.61–5.49 (m, 1H), 5.41–5.27 (m, 2H), 2.16–2.00 (m, 1H), 1.34–1.31 (d, J = 6.4 Hz, 3H), 0.99–0.94 (dd, J = 6.8, 6.2 Hz, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 209.9, 166.5, 134.4–123.6, 86.6, 40.9, 32.6, 18.4–15.8.

S-(Cyanomethyl) O-(3-Methylbutan-2-yl) Carbonodithioate (XA6)

Bromoacetonitrile (4.8 g, 40 mmol) was added dropwise to a stirred solution of xanthate salt XAK (7.7 g, 38 mmol) in tetrahydrofuran (25 mL) at 0 °C. After stirring for 16 h, the mixture was filtered off to remove the formed KBr. The solvent was concentrated under reduced pressure to yield a yellow oil (7.0 g, 91%). XA6 was used without additional purification. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.59–5.61 (m, 1H), 3.86 (s, 2H), 2.10–1.96 (m, 1H), 1.35–1.33 (d, J = 6.4 Hz, 3H), 0.99–0.97 (d, J = 6.8 Hz, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 208.5, 115.4, 87.8, 32.7, 21.0, 18.4–15.8.

General Procedure for the Synthesis of Monoadducts Using Pathway 1 (M1–21)

The xanthate (1.1 equiv), alkene (1 equiv), and lauroyl peroxide (LPO, 0.15 equiv) were dissolved in toluene (1 mL for 1 g of xanthate) in a Schlenk tube. The solution was degassed with three freeze–pump–thaw cycles and sealed under vacuum. After heating and stirring during 16 h at 90 °C, the reaction mixture was purified by column chromatography.

Analytical Data for the Compounds M11–21

Compounds M1–M10 have been described in our recently published work.[29]

Methyl 4-Butoxy-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)butanoate (M10)

Following the general procedure, compound M10 was obtained using XA1 and n-butyl vinyl ether and isolated after column chromatography (hexane/EtOAc 8:2) in 88% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.63–5.5 (m, 2H), 3.78–3.66 (m, 4H), 3.55–3.42 (m, 1H), 2.82–2.67 (m, 1H), 2.49–2.16 (m, 1H), 1.65–1.33 (m, 3H), 2.12–1.95 (m, 2H), 1.63–1.56 (m, 2H), 1.41–1.31 (m, 5H), 1.25–1.24 (m, 3H), 1.01–0.91 (m, 9H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.1, 176.4–176.1, 90.1–89.4, 85.3–85.2, 69.5, 51.7–51.6, 36.9–36.5, 31.7–32.6, 31.3, 19.2, 18.2–17.9, 17.4, 16.9, 15.8–15.8, 13.8–13.8.

Methyl 5-Butoxy-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)pentanoate (M11)

Following the general procedure, compound M11 was obtained using XA1 and n-butyl allyl ether and isolated after column chromatography (hexane/EtOAc 9:1) in 82% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.60–5.50 (m, 1H), 4.00–3.92 (m, 1H), 3.69–3.68 (m, 3H), 3.57–3.46 (m, 2H), 2.79–2.56 (m, 1H), 2.08–1.96 (m, 2H), 1.69–1.51 (m, 3H), 1.41–1.19 (m, 10H), 0.98–0.89 (m, 9H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 214.7–213.7, 176.5, 86.1–85.1, 72.7–72.7, 70.9–70.9, 51.6, 48.4–47.9, 37.1, 36.1–35.5, 34.2, 32.6–31.7, 19.3, 18.2–15.7, 13.9.

Methyl 7-Bromo-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)heptanoate (M12)

Following the general procedure, compound M12 was obtained using XA1 and 5-bromo-1-pentene and isolated after column chromatography (hexane/EtOAc 95:5) in 49% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.56–5.46 (m, 1H), 3.83–3.68 (m, 1H), 3.65–3.62 (m, 3H), 3.40–3.36 (m, 2H), 2.77–2.61 (m, 1H), 2.14–1.47 (m, 7H), 1.27–1.24 (m, 3H), 1.19–1.15 (m, 3H), 0.93–0.91 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.5, 176.3, 85.7, 51.8, 48.5–48.0, 38.2–37.2, 37.2, 33.5–33.2, 32.7, 30.1–29.8, 18.2–17.9, 17.1–16.7, 15.8–15.7.

Methyl 13-Bromo-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)tridecanoate (M13)

Following the general procedure, compound M13 was obtained using XA1 and 11-bromo-1-undecene and isolated after column chromatography (hexane/EtOAc 95:5) in 80% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.59–5.52 (m, 1H), 3.78–3.77 (m, 1H), 3.66–3.65 (m, 3H), 3.41–3.36 (t, 2H), 2.70–2.63 (m, 1H), 2.08–1.93 (m, 2H), 1.88–1.78 (m, 2H), 1.73–1.52 (m, 3H), 1.47–1.33 (m, 4H), 1.29–1.26 (m, 11H), 1.18–1.16 (m, 3H), 0.95–0.93 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 214.0, 176.66, 85.32, 51.81, 49.30–48.78, 38.27–37.59, 37.38–37.21, 35.36–34.93, 34.09, 32.90, 32.79, 29.48–26.74, 18.34–18.32, 17.19–15.86.

Methyl 13-Hydroxy-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)tridecanoate (M14)

Following the general procedure, compound M14 was obtained using XA1 and 10-undecen-1-ol and isolated after column chromatography (hexane/EtOAc 7:3) in 77% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.57–5.48 (m, 1H), 3.75–3.71 (m, 1H), 3.66–3.64 (m, 3H), 3.62–3.57 (t, 2H), 2.72–2.65 (m, 1H), 2.12–1.91 (m, 2H), 1.80 (s, 1H), 1.73–1.48 (m, 5H), 1.38–1.24 (m, 15H), 1.17–1.15 (m, 3H), 0.94–0.92 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.8–213.7, 176.6, 85.4, 62.9, 51.6, 49.1–48.6, 38.1–37.5, 37.5–37.1, 32.7, 29.5–25.7, 18.2, 17.0–15.8.

Methyl 6-Hydroxy-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)hexanoate (M15)

Following the general procedure, compound M15 was obtained using XA1 and 3-buten-1-ol and isolated after column chromatography (hexane/EtOAc 8:2) in 76% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.57–5.50 (m, 1H), 4.0–3.86 (m, 1H), 3.77–3.72 (m, 2H), 3.67–3.66 (m, 3H), 2.78–2.65 (m, 1H), 2.20–1.86 (m, 4H), 1.72–1.60 (m, 1H), 1.30–1.28 (m, 3H), 1.24 (s, 1H), 1.20–1.18 (m, 3H), 0.96–0.93 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 214.9–214.5, 176.7–176.5, 86.4–85.9, 59.7, 51.8, 46.5–46.1, 38.3–37.9, 37.2, 32.7, 18.2–17.9, 17.0–15.8.

Methyl 6-Hydroxy-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)hexanoate (M16)

Following the general procedure, compound M16 was obtained using XA2 and 3-buten-1-ol and isolated after column chromatography (hexane/EtOAc 6:4) in 65% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.58–5.50 (m, 1H), 4.0–3.93 (m, 1H), 3.79–3.76 (m, 2H), 3.67 (s, 3H), 2.53–2.48 (m, 2H), 2.15–1.86 (m, 7H), 1.31–1.29, 0.96–0.93 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 214.3, 173.5, 86.0, 59.8, 51.7, 47.4, 37.7–37.4, 32.7, 31.4, 29.9, 18.2–17.9, 15.8.

Methyl 9,10-Dihydroxy-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)decanoate (M17)

Following the general procedure, compound M17 was obtained using XA1 and 7-octene-1,2-diol and isolated after column chromatography (DCM/EtOAc 7:3) in 49% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.55–5.50 (m, 1H), 3.79–3.57 (m, 6H), 3.42–3.38 (m, 1H), 2.78–2.72 (s, 2H), 2.71–2.59 (m, 1H), 2.11–1.93 (m, 2H), 1.73–1.57 (m, 3H), 1.47–1.31 (m, 6H), 1.27–1.25 (m, 3H), 1.17–1.15 (m, 3H), 0.94–0.91 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.9, 176.8, 85.5, 72.1, 66.8, 51.8, 49.1–48.6, 37.6–37.1, 37.2, 35.0–34.8, 32.9, 32.7, 26.6–25.4, 18.2–17.9, 17.1–15.8.

Methyl 2-Methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)-10-(oxiran-2-yl)decanoate (M18)

Following the general procedure, compound M18 was obtained using XA1 and 1,2-epoxy-9-decene and isolated after column chromatography (hexane/EtOAc 9:1) in 75% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.58–5.53 (m, 1H), 3.80–3.71 (m, 1H), 3.68–3.66 (s, 3H), 2.95–2.86 (m, 1H), 2.75–2.72 (m, 2H), 2.46–2.45 (m, 1H), 2.12–1.95 (m, 2H), 1.76–1.56 (m, 3H), 1.55–1.27 (m, 13H), 1.20–1.17 (m, 3H), 0.96–0.94 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.8, 176.4, 85.1, 52.2, 51.7, 49.1–48.6, 47.0, 38.1–37.5, 37.2–37.1, 35.2–34.8, 32.6, 32.4, 29.3–25.8, 18.2–17.8, 17.1–15.7.

Methyl 2-((((3-Methylbutan-2-yl)oxy)carbonothioyl)thio)-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)propanoate (M19)

Following the general procedure, compound M19 was obtained using XA1 and allyl pinacol boronate and isolated after column chromatography (hexane/EtOAc 9:1) in 74% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.59–5.51 (m, 1H), 3.96–3.87 (m, 1H), 3.69–3.65 (s, 3H), 2.67–2.59 (m, 1H), 2.16–1.97 (m, 2H), 1.8–1.71 (m, 1H), 1.31–1.23 (m, 17H), 1.21–1.17 (m, 3H), 0.98–0.94 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.6, 176.6, 85.0, 83.5, 51.7, 45.3–45.0, 40.4–39.4, 37.4, 32.7, 24.8, 18.2–18.0, 17.1–15.8.

Methyl-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)-7-((2-oxo-2H-chromen-4-yl)oxy)heptanoate (M20)

Following the general procedure, compound M20 was obtained using XA1 and 4-(pent-4-en-1-hydroxy)2H-chromen-2-one and isolated after column chromatography (hexane/EtOAc 8:2) in 37% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 7.81–7.24 (m, 4H), 5.66 (s, 1H), 5.58–5.53 (m, 1H), 4.17–4.13 (m, 2H), 3.93–3.78 (m, 1H), 3.67 (s, 3H), 2.78–2.65 (m, 1H), 2.21–1.59 (m, 7H), 1.30–1.27 (m, 3H), 1.22–1.19 (m, 3H), 0.96–0.93 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.6, 176.3, 165.5, 162.8, 153.3, 132.4–116.7, 115.7, 90.5, 85.8, 68.8, 51.8, 48.9–48.4, 38.0–37.3, 37.2, 32.7, 31.9–31.4, 25.8, 18.2–17.1, 15.7.

Dimethyl 2,6-Dimethyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)heptanedioate (M21)

Following the general procedure, compound M21 was obtained using XA1 and methyl 2-methyl-4-pentenoate and isolated after column chromatography (hexane/EtOAc 9:1) in 73% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.62–5.49 (m, 1H), 3.69–3.60 (m, 1H), 3.68–3.67 (m, 6H), 2.73–2.64 (m, 2H), 2.18–1.51 (m, 5H), 1.30–1.25 (m, 3H), 1.20–1.18 (m, 6H), 0.96–0.94 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.5, 176.3, 85.7–85.5, 51.7, 47.3–46.8, 39.1–38.5, 38.0, 32.7, 18.2–17.9, 17.1–15.7.

General Procedure for the Synthesis of Monoadducts Using Pathway 2 (M22–23)

Xanthate (1.1 equiv), methyl 2-methyl-4-pentenoate (1 equiv), and lauroyl peroxide (LPO, 0.15 equiv) were dissolved in toluene (1 mL for 1 g of xanthate) in a Schlenk tube. The solution was degassed with three freeze–pump–thaw cycles and sealed under vacuum. After heating and stirring during 16 h at 90 °C, the reaction mixture was purified by column chromatography.

Analytical Data for Compounds M22 and M23

Methyl-6-(1,3-dioxoisoindolin-2-yl)-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)hexanoate (M22)

Following the general procedure, compound M22 was obtained using XA5 and after column chromatography (hexane/EtOAc 8:2) in 40% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 7.86–7.67 (m, 4H), 5.56–5.40 (m, 1H), 3.86–3.70 (m, 3H), 3.67–3.62 (m, 3H), 2.80–2.60 (m, 1H), 2.26–1.26 (m, 5H), 1.29–1.15 (m, 6H), 0.92–0.86 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 213.2, 176.4, 168.2, 133.9–123.2, 85.7, 51.7, 46.9–46.2, 37.2, 37.9–33.5, 32.7, 18.2–15.8.

Methyl 6-Cyano-2-methyl-4-((((3-methylbutan-2-yl)oxy)carbonothioyl)thio)hexanoate (M23)

Following the general procedure, compound M23 was obtained using XA6 and after column chromatography (hexane/EtOAc 8:2) in 79% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.59–5.47 (m, 1H), 3.94–3.74 (m, 1H), 3.67–3.66 (m, 3H), 2.76–2.60 (m, 1H), 2.54–2.45 (m, 2H), 2.19–1.93 (m, 4H), 1.78–1.52 (m, 1H), 1.31–1.27 (m, 3H), 1.20–1.18 (d, 3H), 0.95–0.94 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 212.4, 176.1, 119.1, 86.4, 48.3–47.5, 37.7, 37.0, 32.7, 31.6–30.9, 18.3–15.7, 14.8.

General Procedure for the Synthesis of Thiolactones (TL1–23)

The corresponding monoadduct was placed in a Schlenk tube, sealed under vacuum, and immersed into a dry bath maintained at 190 °C. After heating during 15 min, it was cooled down and evacuated under vacuum to remove the formed COS, 2-methylbut-2-ene, and methanol; this cycle was reproduced three times. Then, the reaction was heated until total cyclization with periodical cooling down and evacuated to remove the formed methanol. Finally, the crude product was purified by column chromatography.

Analytical Data for Compounds TL1–23

Compounds TL1–TL9 have been described in our recently published work.[29]

5-(Butoxymethyl)-3-methyldihydrothiophen-2(3H)-one (TL11)

Following the general procedure, compound TL11 was obtained after 16 h and column chromatography (hexane/EtOAc 4:6) in 89% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 4.06–3.46 (m, 5H), 2.77–2.38 (m, 1.5H), 1.67–1.51 (m, 2H), 1.41–1.17 (m, 6.5H), 0.95–0.88 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 210.5–209.3, 77.5–76.7, 74.2–71.3, 48.9–44.8, 37.2–35.7, 31.9–29.3, 23.0–19.3, 15.3–13.9.

5-(9-Bromononyl)-3-methyldihydrothiophen-2(3H)-one (TL13)

Following the general procedure, compound TL13 was obtained after 6 h and column chromatography (hexane/EtOAc 9:1) in 52% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.79–3.66 (m, 1H), 3.42–3.38 (t, 2H), 2.74–2.49 (m, 1.5H), 2.18–2.02 (m, 1H), 1.89–1.80 (m, 2H), 1.80–1.74 (m, 2H), 1.59–1.19 (m, 13H), 1.19–1.15 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.0–209.9, 48.8–45.5, 41.4, 39.5, 36.7–36.4, 34.0–32.8, 29.3–28.1, 15.4–14.5. HRMS calcd for [C14H25BrOS + H]+: 321.0888; found: 321.0878.

5-(9-Hydroxynonyl)-3-methyldihydrothiophen-2(3H)-one (TL14)

Following the general procedure, compound TL14 was obtained after 8 h and column chromatography (hexane/EtOAc 5:5) in 91% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.74–3.63 (m, 1H), 3.58–3.53 (t, 2H), 2.72–2.43 (m, 1.5H), 2.24 (s, 1H), 2.15–1.95 (m, 1H), 1.74–1.60 (m, 2H), 1.52–1.42 (m, 2.5H), 1.37–1.20 (m, 12H), 1.12–1.09 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.3–210.2, 62.8, 48.8–45.5, 41.4–39.5, 36.7–36.3, 32.7, 29.4–25.7, 15.4–14.4. HRMS calcd for [C14H26O2S + H]+: 259.1760; found: 259.1764.

5-(2-Hydroxyethyl)-3-methyldihydrothiophen-2(3H)-one (TL15)

Following the general procedure, compound TL15 was obtained after 8 h and column chromatography (hexane/EtOAc 5:5) in 92% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 4.01–3.68 (m, 3H), 2.75–2.53 (m, 1.5H), 2.26–1.91 (m, 2.5H), 1.68–1.52 (m, 2H), 1.21–1.17 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.6–210.6, 62.7, 48.5, 45.4–43.8, 41.5, 39.5–39.0, 15.4–14.4. HRMS calcd for [C7H12O2S + H]+: 161.0636; found: 161.0631.

5-(2-Hydroxyethyl)dihydrothiophen-2(3H)-one (TL16)

Following the general procedure, compound TL16 was obtained after 9 h and column chromatography (hexane/EtOAc 4:6) in 71% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 4.07–3.99 (m, 1H), 3.79–3.66 (m, 2H), 2.06 (s, 1H), 2.61–2.55 (m, 2H), 2.55–2.40 (m, 1H), 2.12–1.86 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 209.30, 60.73, 47.90, 41.79, 39.98, 32.26. HRMS calcd for [C6H10O2S + H]+: 147.0480; found: 147.0483.

5-(5,6-Dihydroxyhexyl)-3-methyldihydrothiophen-2(3H)-one (TL17)

Following the general procedure, compound TL17 was obtained after 8 h and column chromatography (DCM/EtOAc 5:5) in 92% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.77–3.67 (m, 3H), 3.45–3.39 (m, 1H), 2.74–2.47 (m, 1.5H), 2.31 (s, 2H), 2.20–2.02 (m, 1H), 1.82–1.68 (m, 2H), 1.55–1.36 (m, 7H), 1.19–1.15 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.4–210.2, 72.1, 66.7, 48.5–45.5, 41.3–39.5, 36.7–36.3, 32.8, 28.5–25.3, 15.4–14.4. HRMS calcd for [C11H20O3S + H]+: 233.1211; found: 233.1209.

3-Methyl-5-(6-(oxiran-2-yl)hexyl)dihydrothiophen-2(3H)-one (TL18)

Following the general procedure, compound TL18 was obtained after 7 h and column chromatography (hexane/EtOAc 7:3) in 67% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.81–3.70 (m, 1H), 2.95–2.89 (m, 1H), 2.78–2.75 (m, 1H), 2.74–2.56 (m, 1.5H), 2.49–2.46 (m, 1H), 2.22–2.04 (m, 1H), 1.80–1.70 (m, 2H), 1.60–1.38 (m, 10.5H), 1.21–1.17 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.0–209.9, 52.3, 48.8–47.1, 47.1, 41.4–39.5, 36.7–36.3, 32.4, 29.2–25.9, 15.4–14.4. HRMS calcd for [C13H22O2S + H]+: 243.1419; found: 243.1414.

3-Methyl-5-((4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)methyl)dihydrothiophen-2(3H)-one (TL19)

Following the general procedure, compound TL19 was obtained after 7 h and column chromatography (hexane/EtOAc 8:2) in 62% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 4.04–3.88 (m, 1H), 2.79–2.55 (m, 1.5H), 2.13–2.09 (m, 1H), 1.51–1.25 (m, 2.5H), 1.25–1.22 (m, 12H), 1.19–1.14 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.4–210.5, 86.7, 49.4–45.5, 43.7–43.4, 43.6, 41.8, 24.8, 15.2–14.4. HRMS calcd for [C12H21BO3S + H]+: 257.1383; found: 257.1380.

4-(3-(4-Methyl-5-oxotetrahydrothiophen-2-yl)propoxy)-2H-chromen-2-one (TL20)

Following the general procedure, compound TL20 was obtained after 8 h and column chromatography (hexane/EtOAc 4:6) in 57% yield as a yellow oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 7.80–7.24 (m, 4H), 5.66 (s, 1H), 4.18–4.14 (m, 2H), 3.88–3.79 (m, 1H), 2.81–2.55 (m, 1.5H), 2.28–1.95 (m, 5H), 1.62–1.50 (m, 0.5H), 1.24–1.17 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 210.3–209.1, 165.5, 163.0, 153.2, 132.5–122.9, 116.7, 90.5, 62.8, 48.5, 45.4–43.9, 41.2–39.5, 33.4–33.0, 27.5–27.3, 15.3–14.4. HRMS calcd for [C17H18O4S + H]+: 319.1004; found: 319.0999.

Methyl 2-Methyl-3-(4-methyl-5-oxotetrahydrothiophen-2-yl)propanoate (TL21)

Following the general procedure, compound TL21 was obtained after 48 h and column chromatography (hexane/EtOAc 8:2) in 89% yield as a colorless oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 4.79–3.66 (m, 1H), 3.64–3.63 (m, 3H), 2.71–2.42 (m, 2.5H), 2.22–1.65 (m, 3H), 1.50–1.38 (m, 0.5H), 1.17–1.09 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 210.2–209.0, 175.9, 51.9, 48.6–48.5, 45.6–44.4, 41.3–39.6, 38.7–37.9, 18.0–14.3. HRMS calcd for [C10H16O3S + H]+: 217.0898; found: 217.0889.

2-(2-(4-Methyl-5-oxotetrahydrothiophen-2-yl)ethyl)isoindoline-1,3-dione (TL22)

Following the general procedure, compound TL22 was obtained after 24 h and precipitation in EtOAc in 30% yield as a white powder. 1H NMR (300 MHz, CDCl3) δ (ppm) = 7.77–7.64 (m, 4H), 3.80–3.61 (m, 3H), 2.68–2.45 (m, 1.7H), 2.15–2.01 (m, 2.6H), 1.55–1.06 (m, 0.8H), 1.11–1.06 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 210.0–209.0, 168.2, 134.2–123.3, 48.3, 45.0–44.5, 40.9–39.1, 36.5–35.4, 15.2–14.4. HRMS calcd for [C15H15NO3S + H]+: 189.0773; found: 289.0782.

3-(4-Methyl-5-oxotetrahydrothiophen-2-yl)propanenitrile (TL23)

Following the general procedure in 1,2-dichlorobenzene with a 1 mol L–1 monoadduct concentration, compound TL23 was obtained after 24 h and column chromatography (hexane/EtOAc 6:4) in 70% yield as a brown oil. 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.87–3.73 (m, 1H), 3.69–1.91 (m, 6.5H), 1.51–1.39 (m, 0.5H), 1.10–1.07 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 209.1–208.0, 118.7, 48.7, 45.4–44.9, 40.3–38.7, 32.1–31.6, 16.1–15.0, 15.1–14.3. HRMS calcd for [C8H11NOS + H]+: 170.0640; found: 170.0643.

Procedure for the Synthesis of Thiolactone TL24

5-(9-Azidononyl)-3-methyldihydrothiophen-2(3H)-one (TL24)

A solution of sodium azide (NaN3, 0.15 g, 2.3 mmol) in H2O (1.5 mL) was prepared and added to a stirred solution of thiolactone TL13 (0.5 g, 1.5 mmol) in acetone (10 mL). The mixture was stirred at refluxing temperature for 6 h and then cooled down to room temperature. The reaction mixture was diluted with 30 mL of diethyl ether and extracted with deionized water (2 × 20 mL) and dried over anhydrous MgSO4. Solvent was removed under reduced pressure, and the crude product was purified by column chromatography (hexane/EtOAc 9:1). TL24 was obtained as a colorless oil (0.31 g, 86%). 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.78–3.62 (m, 1H), 3.27–3.22 (t, 2H), 2.76–2.46 (m, 1.5H), 2.18–2.02 (m, 1H), 1.99–1.78 (m, 2H), 1.78–1.69 (m, 2H), 1.58–1.18 (m, 13H), 1.18–1.14 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.0–209.9, 51.5, 48.8–45.5, 41.4, 39.6, 36.7–36.4, 29.1–26.7, 15.4–14.4. HRMS calcd for [C14H25N3OS + H]+: 284.2039; found: 284.2035.

Procedure for the Synthesis of Thiolactone TL25

S-(9-(4-Methyl-5-oxotetrahydrothiophen-2-yl)nonyl) Ethanesulfonothioate (TL25)

A solution of S-sodium ethanethiosulfonate (0.91 g, 6.2 mmol) in DMF (3 mL) was prepared and added to a stirred solution of thiolactone TL13 (1 g, 3.1 mmol) in DMF (3 mL). The mixture was stirred at 40 °C for 24 h. The reaction mixture was diluted with 50 mL of diethyl ether and extracted with deionized water (3 × 30 mL) and dried over anhydrous MgSO4. Solvent was removed under reduced pressure, and the crude product was purified by column chromatography (hexane/EtOAc 6:4). TL25 was obtained as a colorless oil (1.1 g, 96%). 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.77–3.66 (m, 1H), 3.33–3.26 (q, J = 7.3 Hz, 2H), 3.12–3.07 (m, 2H), 2.70–2.46 (m, 1.5H), 2.18–2.01 (m, 1H), 1.79–1.53 (m, 4H), 1.46–1.41 (t, J = 7.3 Hz, 3H), 1.23–1.17 (m, 13H), 1.17–1.13 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.1–210.0, 57.0, 48.8–45.5, 41.4, 39.5, 36.7–36.2, 29.7–28.2, 15.4–14.4. HRMS calcd for [C16H30O3S3 + H]+: 367.1435; found: 367.1428.

Procedure for the Synthesis of Thiolactone TL26

S-(9-(4-Methyl-5-oxotetrahydrothiophen-2-yl)nonyl)-O-(3-methylbutan-2-yl)carbonodithioate (TL26)

Xanthate salt XAK (0.47 g, 2.3 mmol) was added portionwise to a stirred solution of thiolactone TL13 (0.5 g, 1.55 mmol) in acetone (15 mL) at 0 °C. After stirring for 16 h, the mixture was diluted with 15 mL of diethyl ether, extracted with deionized water (3 × 20 mL), and dried over anhydrous MgSO4. Solvent was removed under reduced pressure to yield TL26 as a yellow oil (0.55 g, 91%). 1H NMR (300 MHz, CDCl3) δ (ppm) = 5.62–5.54 (m, 1H), 3.81–3.66 (m, 1H), 3.13–3.08 (m, 2H), 2.79–2.46 (m, 1.5H), 2.24–1.94 (m, 2H), 1.83–1.65 (m, 4H), 1.58–1.22 (m, 17H), 1.22–1.16 (m, 3H), 1.00–0.97 (m, 6H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 214.7, 211.0–209.9, 85.2, 48.8–45.5, 42.1, 39.6, 36.7–36.4, 35.5, 32.7, 29.3–28.4, 18.2–18.0, 15.8–14.5. HRMS calcd for [C20H36O2S3 + H]+: 405.1956; found: 405.1950.

Procedure for the Synthesis of Thiolactone TL27

5-(9-Mercaptononyl)-3-methyldihydrothiophen-2(3H)-one (TL27)

Thiolactone TL26 (0.250 g, 0.6 mmol) was placed in a Schlenk tube, sealed under vacuum, and immersed into a dry bath maintained at 190 °C. After heating during 15 min, it was cooled down and evacuated under vacuum to remove formed COS, 2-methylbut-2-ene, and methanol; this cycle was reproduced three times. Then, the reaction was heated during 4 h with periodical cooling down and evacuated to remove formed methanol. TL27 was obtained as a colorless oil (0.15 g, 87%). 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.84–3.68 (m, 1H), 2.76–2.60 (m, 1.5H), 2.57–2.52 (m, 2H), 2.22–2.02 (m, 1H), 1.81–1.68 (m, 2H), 1.65–1.60 (m, 2H), 1.53–1.22 (m, 13H), 1.19–1.15 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 211.0–209.9, 48.8–45.5, 41.4, 39.5, 36.7–36.4, 34.0, 29.4–28.2, 24.6, 15.4–14.5.

Procedure for the Synthesis of Tetrahydrothiophene Derivative (THT1)

Methyl 2-Methyl-3-(tetrahydrothiophen-2-yl)propanoate (THT1)

Monoadduct M12 (1.2 g, 3 mmol) was placed in a Schlenk tube, sealed under vacuum, and immersed into a dry bath maintained at 190 °C. After heating during 15 min, it was cooled down and evacuated under vacuum, and this cycle was reproduced three times. Then, the reaction was heated until total cyclization with periodical cooling down and evacuated under vacuum. Finally, crude reaction was purified by column chromatography (hexane/EtOAc 8:2), and THT1 was obtained as a colorless oil (0.49 g, 88%). 1H NMR (300 MHz, CDCl3) δ (ppm) = 3.64–3.63 (s, 3H), 3.39–3.24 (m, 1H), 2.88–2.73 (m, 2H), 2.59–2.46 (m, 1H), 2.13–1.98 (m, 2.5H), 1.91–1.79 (m, 1.5H), 1.73–1.64 (m, 0.5H), 1.58–1.45 (m, 1.5H), 1.15–1.11 (m, 3H). 13C NMR (75 MHz, CDCl3) δ (ppm) = 176.7, 51.6–51.5, 47.1, 46.3, 41.9, 41.2, 39.2, 38.7, 37.5, 37.3, 32.2, 30.2, 30.1, 18.0, 16.6. HRMS calcd for [C9H16O2S – H]−: 187.0786; found: 187.0789.