Regio- and stereoselective syntheses of allylic thioethers under metal free conditions

Abstract

A metal free, regio and stereoselective syntheses of allylic thioethers using allyl iodides and aryl or alkyl disulfides as coupling partners is described. The densely functionalized allyl iodides having different stereochemistry (E & Z) reacted well with a variety of disulfides in a regio and stereoselective manner providing the resulting allyl aryl thioethers in 62–92% yields.

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Introduction

Due to environmental concerns and cost issues, the metal-free organic transformations are in great need. Enough progress has been made in this direction by using various catalytic systems in recent years;¹ the peroxide alone or with additives has emerged as the perfect substitute to the traditional transition metal catalysis for several organic transformations.² Meanwhile, aryl thioethers have been found to play important roles in organic synthesis, the pharmaceutical industry and materials science.^3,4 Various transition metals such as Pd,^5a–d Cu,^5e–g Fe,^5h,i Ni,^5j,k In,^5l Co,^5m Au,⁵ⁿ Ag,^5o Mg^5p etc. have been used so far for the syntheses of thioethers via C–S bond formation between aryl halides or pseudo halides and thiols.⁶ Recently, the syntheses of aryl thioethers and thioesters have been reported under metal-free conditions via C–H functionalization using a variety of sulphur surrogates.^7,8 Various catalyst or catalytic systems such as DTBP,^7a,c,d,f,g TBHP,^7h,i K₂S₂O₈,^7j–l AcOOH,^8c etc. have been used so far for the syntheses of thioethers via C–H functionalization. In the case of syntheses of allyl aryl thioethers, various metals such as Rh,^9a In,^9b Co,^9c Ni,^9d etc. were used for the C–S coupling between allyl halides/acetates and disulfides (Scheme 1). A palladium acetate catalyzed synthesis of allyl aryl thioethers via cross-coupling reaction between Baylis–Hillman acetates and diphenyl disulfides was reported by Sreedhar and co-workers (Scheme 1).^9e The syntheses of allyl aryl thioethers via the C–S bond formation between allyl halides and sulphur surrogate under metal free conditions is not well studied. Therefore, we have decided to find out suitable methodology for the synthesis of allylic thioethers and herein report the first regio- and stereoselective syntheses of allylic thioethers via C–S bond formation between densely functionalized allyl iodides and disulfides under metal free conditions (Scheme 2).

Scheme 1 Syntheses of allylic thioethers.

Scheme 2 Synthesis of allyl aryl thioethers 4a.

Results and discussion

Accordingly, we have selected the allyl iodide 1a (2.0 mmol) and diphenyl disulfide 2a (1.0 mmol) as model substrate and treated them under the influence of DCP (dicumyl peroxide, 10.0 mmol) using CH₃CN as solvent at 80 °C for 48 h. The data collection of isolated product revealed the formation of only allyl phenyl thioether 4a in 42% yield (Table 1, entry 1). There was no formation of the thioethers 3a and 3b which were confirmed by GCMS of crude reaction mixture. It is to note here that complete retention in stereochemistry across the double bond was obtained in this reaction i.e. Z-selectivity.

Table 1 Optimization of the reaction conditions^a

Entry	Oxidant (equiv.)	Time (h)	Yield^b (%)
a Reaction conditions: allyl iodide 1a (2.0 mmol), diphenyl disulfide 2a (1.0 mmol) and oxidant (10.0 mmol) were reacted in CH3CN (2.0 mL) at 80 °C for 12 h.b Isolated yields are based on 1a.c TBHP solution in water.d 2.0 mmol of 2a was used.e 120 °C.f 1.0 mL CH3CN was used.g 2.0 equivalent of DTBP was used.
1	DCP (5.0)	12	42
2	BPO (5.0)	12	36
3	K2S2O8 (5.0)	12	30
4	H2O2 (5.0)	12	51
5^c	TBHP (5.0)	12	58
6	TBPB (5.0)	12	55
7	DTBP (5.0)	12	60
8	DTBP (5.0)	48	68
9^d	DTBP (5.0)	48	88
10^e	DTBP (5.0)	48	82
11^f	DTBP (5.0)	48	76
12^g	DTBP (2.0)	48	48

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Encouraged by these results, we decided to optimize the reaction conditions for this fascinating C–S bond formation strategy. Accordingly, a variety of oxidants were employed to catalyze the reaction between 1a and 2a (Table 1). Oxidant such as BPO (benzoyl peroxide), K₂S₂O₈ could not provide the encouraging results (entries 2 & 3). H₂O₂, TBHP (tert-butyl hydroperoxide) and TBPB (tert-butyl peroxybenzoate) provided slightly better results (entries 4–6). The DTBP (di-tert-butyl peroxide) provided the desired product in 60% yield after 12 h (entry 7). When the same reaction was carried out for 48 h under the influence of DTBP, provided the thioether 4a in 68% yield (entry 8). Interestingly, when the amount of disulfide was doubled, thioether 4a was obtained in 88% yield (entry 9). Enhancement in the reaction temperature could not increase the yield significantly (entry 10). Diminishing the CH₃CN and DTBP amounts were not found favourable for this coupling between 1a and 2a (entry 11 & 12).

Once we have optimized reaction conditions in hand (Table 1, entry 9), we then studied the substrate scope for this interesting C–S bond formation. Accordingly, a variety of allyl iodides 1 and 5 were synthesized from the Baylis–Hillman alcohols following the literature procedures.^10a,b It is worth mentioning here that Baylis–Hillman adducts or their derivatives possessing ester functionality (obtained from alkyl acrylates) and nitrile functionality (obtained from acrylonitrile) be evidence for remarkable opposite stereochemical directions in various organic transformations.^10a,b,11 This effect of reversibility might be attributed to the steric difference between the nitrile (smaller) and ester (larger) functionalities. The alcohols possessing ester functionality provided the allyl iodides as Z-isomer¹² only whereas the alcohols possessing nitrile functionality provided allyl iodides as E-isomer. Therefore, Z-isomer of allyl iodides 1 and E-isomer of allyl iodide 5 was used as coupling partner for C–S bond formation with disulfides.

Firstly, the various allyl iodides possessing ester functionality with Z stereochemistry were treated with different disulfides 2 under the influence of DTBP following the optimized reaction conditions, provided the resulting allylic thioethers 4 in 62–85% isolated yields. The structures of these allylic thioethers 4 were determined from their spectral (¹H NMR, ¹³C NMR and MS) data which suggested complete retention in stereochemistry across the double bond in the products i.e. Z-stereochemistry were observed (in ¹H NMR the olefinic proton appeared at δ 7.64–7.81 range confirm Z-stereochemistry).^10a,b,11 Allyl iodides possessing substitutes at o/m/p-position underwent regio- and stereo selective C–S coupling reaction with both aryl and alkyl disulfides to provide the desired allyl aryl thioethers (4a–d & 4f–r) and allyl alkyl thioethers (4e & 4s–v) in good to excellent yields. We have also employed the allyl iodides 1 (E-isomer) possessing alkyl group instead that of aryl group for the C–S bond formation with disulfides under the optimized reaction conditions, provided the desired allyl aryl thioethers 4w and 4x in 72% and 70% yields respectively. In these case also complete retention in stereochemistry across the double bond in the products i.e. E-stereochemistry were observed.¹²

Subsequently, we have employed the densely functionalized E-allyl iodides 5 possessing nitrile functionality for the C–S coupling with variety of disulfides 2 under the influence of DTBP following the optimized reaction conditions. Both the aryl and alkyl disulfide coupled well with allyl iodides 5 to provide the resulting allylic thioethers 6 in 72–92% yield. Substrates possessing substituent at o, m, p position of phenyl ring coupled well under the reaction conditions employed. The structures of these allylic thioethers 6 were determined from their spectral (¹H NMR, ¹³C NMR and MS) data which suggest that a complete retention in stereochemistry across the double bond in the products i.e. E-stereochemistry were observed (in ¹H NMR the olefinic proton appeared at δ 6.47–6.76 range confirm E-stereochemistry).^10a,b,11

To establish a possible reaction pathway for this methodology, we have performed few control experiments as shown in Scheme 3. Initially, we have performed the C–S coupling reaction between allyl iodide 1a and disulfide 2a in absence of DTBP under optimized reaction conditions and observed that no reaction took place (Path A, Scheme 3). Next, the same reaction was carried out in presence of TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) using optimized reaction conditions which provided the allylic thioether 4a in 76% isolated yield (Path B, Scheme 3). It was found that the TEMPO coupled well with allyl iodide 1a under same reaction conditions to provide coupled product 7 in 82% isolated yield (Path C, Scheme 3). On the basis of these control experiments we proposed plausible mechanism which follows the radical pathway (Scheme 4).

Scheme 3 Control experiments.

Scheme 4 Plausible mechanism for the synthesis of thioether 4a.

A plausible mechanism for the syntheses of allylic thioethers is presented in the Scheme 4 by taking 4a as model case. In the presence of DTBP, the allyl iodide 1a generated allyl radical A. At the same time disulfide converted into phenyl sulphide radical. The coupling of allyl radical A with phenyl sulphide radical yielded into the resulting thioether 4a.

Conclusions

In conclusions, we have developed a methodology for the synthesis of allylic thioethers via C–S bond formation between allyl iodides and disulfides under metal free conditions for the first time. A variety of densely functionalized allyl iodides and disulfides coupled well under the influence of DTBP provided the thioethers in 62–92% yield. A complete stereo- and regioselectivity were observed in these transformations.

Experimental

General information

All chemicals were purchased from commercial suppliers and used without further purification. NMR spectra were recorded on a Jeol resonance-400 instrument using CDCl₃ as solvent. Chemical shifts are reported in parts per million (ppm) and referenced to the residual solvent resonance. Coupling constant (J) are reported in hertz (Hz). Standard abbreviations indicating multiplicity were used as follows: s = singlet, d = doublet, t = triplet, dd = double doublet, q = quartet, m = multiplet. HRMS data were collected on Waters – Xevo G2S QTof with UPLC H-Class Ultra Performance Liquid chromatography-mass spectrometry (LC-MS) facility.

General procedure for Table 1

To a stirred solution of allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol) and diphenyl disulfide (2.0 mmol, 0.436 g) in CH₃CN (2.0 mL) was added oxidant (10.0 mmol) and then the reaction mixture was stirred for 80 °C under nitrogen atmosphere for 48 h. The solvent was then removed under reduced pressure and the crude product thus obtained was purified by column chromatography (silica gel, 1% EtOAc in hexanes) to provide the allyl thioether 4a as pale yellow colour liquid.

Representative example of Table 1: methyl-(Z)-3-phenyl-2-((phenylthio)methyl)acrylate (entry 9, 4a)^10c

The title compound was prepared following the general procedure for Table 1, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), diphenyl disulfide (2.0 mmol, 0.436 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4a as pale yellow liquid. Yield: 0.499 g, 88%; ¹H NMR (400 MHz, CDCl₃): δ 3.77 (s, 3H), 4.05 (s, 2H), 7.20–7.32 (m, 3H), 7.38–7.42 (m, 7H), 7.79 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.3, 52.3, 126.8, 128.2, 128.7, 129.0, 129.1, 129.6, 130.7, 134.8, 136.0, 141.6, 167.6.

General procedure for Table 2

To a stirred solution of allyl iodide 1 (2.0 mmol) and disulfide (2.0 mmol) in CH₃CN (2.0 mL) was added DTBP (10.0 mmol), then the reaction mixture was stirred for 48 h at 80 °C under nitrogen atmosphere. The solvent was then removed under reduced pressure and the crude product thus obtained was purified by column chromatography (silica gel, 1% EtOAc in hexanes) to provide the allyl thioether 4.

Methyl-(Z)-2-(((4-chlorophenyl)thio)methyl)-3-phenylacrylate (4b). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), bis(4-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4b as pale yellow liquid. Yield: 0.522 g, 82%; ¹H NMR (400 MHz, CDCl₃): δ 3.77 (s, 3H), 3.98 (s, 2H), 7.11 (d, J = 8.8 Hz, 2H), 7.21 (d, J = 8.8 Hz, 2H), 7.30–7.32 (m, 5H), 7.73 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.5, 52.3, 128.0, 128.7, 129.0, 129.1, 129.4, 132.4, 132.9, 134.3, 134.7, 141.6, 167.4; HRMS (ESI) exact mass calcd for C₁₇H₁₅ClO₂S + K (M + K), 357.0118; found: 357.0127.

Table 2 DTBP-promoted C–S bond formation between allyl iodides 1 and disulfides 2^a,b

a Reaction conditions: allyl iodide 1 (2.0 mmol), disulfide 2 (2.0 mmol) and DTBP (10.0 mmol) were reacted in CH3CN (2.0 mL) at 80 °C for 48 h.b Isolated yields are based on allyl iodide 1.

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Methyl-(Z)-2-(((4-bromophenyl)thio)methyl)-3-phenylacrylate (4c). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), bis(4-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4c as pale yellow liquid. Yield: 0.515 g, 71%; ¹H NMR (400 MHz, CDCl₃): δ 3.80 (s, 3H), 4.00 (s, 2H), 7.16 (d, J = 8.8 Hz, 2H), 7.29 (d, J = 8.8 Hz, 2H), 7.31–7.33 (m, 5H), 7.75 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.3, 52.4, 120.9, 127.9, 128.7, 129.1, 129.4, 131.9, 132.5, 141.7, 167.5; HRMS (ESI) exact mass calcd for C₁₇H₁₅BrO₂S + Na (M + Na), 384.9874; found: 384.9881.

Methyl-(Z)-2-(((3-chlorophenyl)thio)methyl)-3-phenylacrylate (4d). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), bis(3-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4d as pale yellow liquid. Yield: 0.433 g, 68%; ¹H NMR (400 MHz, CDCl₃): δ 3.82 (s, 3H), 4.05 (s, 2H), 7.08–7.24 (m, 3H), 7.26–7.42 (m, 6H), 7.79 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 31.9, 52.4, 126.7, 127.7, 128.3, 128.8, 129.2, 129.4, 129.8, 129.9, 134.61, 134.65, 138.2, 142.0, 167.5; HRMS (ESI) exact mass calcd for C₁₇H₁₅ClO₂S + Na (M + Na), 341.0379; found: 341.0367.

Methyl-(Z)-2-((cyclohexylthio)methyl)-3-phenylacrylate (4e). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), dicyclohexyl disulfide (2.0 mmol, 0.44 mL), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4e as pale yellow liquid. Yield: 0.359 g, 62%; ¹H NMR (400 MHz, CDCl₃): δ 1.06–1.38 (m, 6H), 1.62–1.75 (m, 2H), 1.78–1.93 (m, 2H), 2.61–2.66 (m, 1H), 3.61 (s, 2H), 3.79 (s, 3H), 7.25–7.40 (m, 3H), 7.41–7.52 (m, 2H), 7.68 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 25.9, 26.1, 26.9, 33.5, 44.5, 52.2, 128.6, 128.9, 129.5, 129.7, 135.1, 140.3, 167.9; HRMS (ESI) exact mass calcd for C₁₇H₂₂O₂S + Na (M + Na), 313.1238; found: 313.1059.

Methyl-(Z)-3-(4-chlorophenyl)-2-((phenylthio)methyl)acrylate (4f)^10c. The title compound was prepared following the general procedure for Table 2, using allyl iodide 1b i.e. methyl-(Z)-3-(4-chlorophenyl)-2-(iodomethyl)acrylate (2.0 mmol, 0.673 g), diphenyl disulfide (2.0 mmol, 0.436 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4f as pale yellow liquid. Yield: 0.484 g, 76%; ¹H NMR (400 MHz, CDCl₃): δ 3.78 (s, 3H), 3.98 (s, 2H), 7.20–7.282 (m, 3H), 7.34 (s, 4H), 7.36 (d, J = 8.4 Hz, 2H), 7.67 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.3, 52.4, 127.0, 128.8, 128.9, 129.0, 130.8, 131.1, 133.2, 135.0, 135.6, 140.1, 167.4.

Methyl-(Z)-3-(4-chlorophenyl)-2-(((4-chlorophenyl)thio)methyl) acrylate (4g). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1b i.e. methyl-(Z)-3-(4-chlorophenyl)-2-(iodomethyl)acrylate (2.0 mmol, 0.673 g), bis(4-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4g as pale yellow liquid. Yield: 0.600 g, 85%; ¹H NMR (400 MHz, CDCl₃): δ 3.77 (s, 3H), 3.93 (s, 2H), 7.14 (d, J = 8.8 Hz, 2H), 7.222 (d, J = 8.8 Hz, 2H), 7.228 (d, J = 8.8 Hz, 2H), 7.28 (d, J = 8.8 Hz, 2H), 7.64 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.5, 52.4, 128.5, 128.9, 129.0, 130.6, 132.6, 133.0, 133.2, 133.9, 135.1, 140.2, 167.2; HRMS (ESI) exact mass calcd for C₁₇H₁₄Cl₂O₂S + Na (M + Na), 374.9989; found: 374.9922.

Methyl-(Z)-3-(4-chlorophenyl)-2-(((3-chlorophenyl)thio)methyl) acrylate (4h). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1b i.e. methyl-(Z)-3-(4-chlorophenyl)-2-(iodomethyl)acrylate (2.0 mmol, 0.673 g), bis(3-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4h as pale yellow liquid. Yield: 0.480 g, 68%; ¹H NMR (400 MHz, CDCl₃): δ 3.77 (s, 3H), 3.96 (s, 2H), 7.05–7.20 (m, 3H), 7.22–7.36 (m, 5H), 7.66 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 31.8, 52.5, 126.9, 128.2, 128.5, 129.0, 129.9, 130.0, 130.7, 133.0, 134.6, 135.2, 137.8, 140.5, 167.1; HRMS (ESI) exact mass calcd for C₁₇H₁₄Cl₂O₂S + Na (M + Na), 374.9989; found: 374.9978.

Methyl-(Z)-2-(((4-bromophenyl)thio)methyl)-3-(4-chlorophenyl) acrylate (4i). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1b i.e. methyl-(Z)-3-(4-chlorophenyl)-2-(iodomethyl)acrylate (2.0 mmol, 0.673 g), bis(4-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4i as yellow solid. Mp: 63 °C; yield: 0.675 g, 85%; ¹H NMR (400 MHz, CDCl₃): δ 3.77 (s, 3H), 3.93 (s, 2H), 7.14 (d, J = 8.4 Hz, 2H), 7.22 (d, J = 8.4 Hz, 2H), 7.27–7.29 (m, 4H), 7.64 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.3, 52.5, 121.2, 128.4, 128.9, 130.6, 131.9, 132.7, 133.0, 134.6, 135.1, 140.2, 167.2; HRMS (ESI) exact mass calcd for C₁₇H₁₄BrClO₂S + K (M + K), 434.9223; found: 434.9227.

Methyl-(Z)-2-((phenylthio)methyl)-3-(p-tolyl)acrylate (4j). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1c i.e. methyl-(Z)-2-(iodomethyl)-3-(p-tolyl)acrylate (2.0 mmol, 0.632 g), diphenyl disulfide (2.0 mmol, 0.436 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4j as pale yellow liquid. Yield: 0.447 g, 75%; ¹H NMR (400 MHz, CDCl₃): δ 2.37 (s, 3H), 3.81 (s, 3H), 4.09 (s, 2H), 7.18 (d, J = 8.4 Hz, 2H), 7.21–7.29 (m, 3H), 7.38 (d, J = 8.4 Hz, 2H), 7.40–7.42 (m, 2H), 7.80 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 21.5, 32.3, 52.3, 126.7, 127.2, 129.0, 129.5, 129.8, 130.6, 132.0, 136.3, 139.4, 141.9, 167.8; HRMS (ESI) exact mass calcd for C₁₈H₁₈O₂S + K (M + K), 337.0665; found: 337.0652.

Methyl-(Z)-2-(((4-chlorophenyl)thio)methyl)-3-(p-tolyl)acrylate (4k). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1c i.e. methyl-(Z)-2-(iodomethyl)-3-(p-tolyl)acrylate (2.0 mmol, 0.632 g), bis(4-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4k as pale yellow liquid. Yield: 0.551 g, 83%; ¹H NMR (400 MHz, CDCl₃): δ 2.35 (s, 3H), 3.79 (s, 3H), 4.03 (s, 2H), 7.15 (d, J = 8.4 Hz, 2H), 7.16 (d, J = 8.4 Hz, 2H), 7.26 (d, J = 8.8 Hz, 2H), 7.29 (d, J = 8.8 Hz, 2H), 7.75 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 21.4, 32.5, 52.2, 127.0, 128.9, 129.4, 129.6, 131.8, 132.2, 132.9, 134.5, 139.4, 141.9, 167.5; HRMS (ESI) exact mass calcd for C₁₈H₁₇ClO₂S + K (M + K), 371.0275; found: 371.0271.

Methyl-(Z)-2-(((4-bromophenyl)thio)methyl)-3-(p-tolyl)acrylate (4l). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1c i.e. methyl-(Z)-2-(iodomethyl)-3-(p-tolyl)acrylate (2.0 mmol, 0.632 g), bis(4-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4l as yellow solid. Mp: 61 °C; yield: 0.505 g, 67%; ¹H NMR (400 MHz, CDCl₃): δ 2.35 (s, 3H), 3.79 (s, 3H), 4.02 (s, 2H), 7.14–7.19 (m, 4H), 7.27–7.31 (m, 4H), 7.74 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 21.5, 32.3, 52.3, 120.8, 126.9, 129.5, 129.6, 131.8, 131.9, 132.3, 135.2, 139.5, 142.0, 167.7; HRMS (ESI) exact mass calcd for C₁₈H₁₇BrO₂S + Na (M + Na), 399.0030; found: 398.9935.

Methyl-(Z)-2-(((3-chlorophenyl)thio)methyl)-3-(p-tolyl)acrylate (4m). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1c i.e. methyl-(Z)-2-(iodomethyl)-3-(p-tolyl)acrylate (2.0 mmol, 0.632 g), bis(3-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4m as pale yellow liquid. Yield: 0.438 g, 66%; ¹H NMR (400 MHz, CDCl₃): δ 2.35 (s, 3H), 3.81 (s, 3H), 4.07 (s, 2H), 7.05–7.24 (m, 5H), 7.25–7.40 (m, 3H), 7.78 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 21.5, 31.9, 52.3, 126.6, 128.1, 129.60, 129.65, 129.67, 129.9, 131.8, 134.6, 138.4, 139.6, 142.2, 167.5; HRMS (ESI) exact mass calcd for C₁₈H₁₇ClO₂S + Na (M + Na), 355.0535; found: 355.0531.

Methyl-(Z)-2-(((3-bromophenyl)thio)methyl)-3-phenylacrylate (4n). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), bis(3-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4n as pale yellow liquid. Yield: 0.566, 78%; ¹H NMR (400 MHz, CDCl₃): δ 3.81 (s, 3H), 4.04 (s, 2H), 7.07 (t, J = 8.0 Hz, 1H), 7.23 (d, J = 8.0 Hz, 1H), 7.29 (d, J = 8.0 Hz, 1H), 7.33–7.44 (m, 5H), 7.46 (s, 1H), 7.79 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.0, 52.4, 122.7, 127.7, 128.8, 128.9, 129.2, 129.4, 129.7, 130.2, 132.7, 134.6, 138.4, 142.0, 167.5; HRMS (ESI) exact mass calcd for C₁₇H₁₅BrO₂S + Na (M + Na), 384.9874; found: 384.9698.

Methyl-(Z)-2-(((3-bromophenyl)thio)methyl)-3-(4-chlorophenyl) acrylate (4o). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1b i.e. methyl-(Z)-3-(4-chlorophenyl)-2-(iodomethyl)acrylate (2.0 mmol, 0.673 g), bis(3-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4o as pale yellow liquid. Yield: 0.635 g, 80%; ¹H NMR (400 MHz, CDCl₃): δ 3.80 (s, 3H), 3.98 (s, 2H), 7.07 (t, J = 8.0 Hz, 1H), 7.21–7.23 (m, 1H), 7.26–7.32 (m, 5H), 7.43 (t, J = 1.6 Hz, 1H), 7.69 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 32.0, 52.5, 122.7, 128.3, 129.0, 129.2, 129.9, 130.2, 130.7, 133.0, 135.2, 138.0, 140.5, 167.2; HRMS (ESI) exact mass calcd for C₁₇H₁₄BrClO₂S + K (M + K), 434.9223; found: 434.9226.

Methyl-(Z)-2-(((3-bromophenyl)thio)methyl)-3-(p-tolyl)acrylate (4p). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1c i.e. methyl-(Z)-2-(iodomethyl)-3-(p-tolyl)acrylate (2.0 mmol, 0.632 g), bis(3-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4p as pale yellow liquid. Yield: 0.467 g, 62%; ¹H NMR (400 MHz, CDCl₃): δ 2.36 (s, 3H), 3.81 (s, 3H), 4.06 (s, 2H), 7.08 (t, J = 8.0 Hz, 1H), 7.17 (d, J = 8.0 Hz, 2H), 7.24–7.32 (m, 4H), 7.46 (t, J = 1.6 Hz, 1H), 7.77 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 21.5, 32.0, 52.4, 122.7, 126.6, 128.7, 129.5, 129.6, 130.1, 131.7, 132.5, 138.6, 139.6, 142.2, 167.6; HRMS (ESI) exact mass calcd for C₁₈H₁₇BrO₂S + Na (M + Na), 399.0030; found: 399.6734.

Methyl-(Z)-2-(((2-bromophenyl)thio)methyl)-3-phenylacrylate (4q). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), bis(2-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4q as pale yellow liquid. Yield: 0.537 g, 74%; ¹H NMR (400 MHz, CDCl₃): δ 3.81 (s, 3H), 4.04 (s, 2H), 7.02 (td, J = 8.0 Hz & 1.6 Hz, 1H), 7.19 (td, J = 8.4 Hz & 1.2 Hz, 1H), 7.27 (dd, J = 6.4 Hz & 1.6 Hz, 1H), 7.32–7.38 (m, 3H), 7.41–7.45 (m, 2H), 7.50 (dd, J = 6.4 Hz & 1.6 Hz, 1H), 7.81 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 31.4, 52.4, 125.1, 127.2, 127.6, 127.8, 128.8, 129.2, 129.5, 130.6, 133.0, 134.6, 137.3, 142.4, 167.5; HRMS (ESI) exact mass calcd for C₁₇H₁₅BrO₂S + K (M + K), 400.9613; found: 400.9681.

Methyl-(Z)-2-(((2-bromophenyl)thio)methyl)-3-(4-chlorophenyl)acrylate (4r). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1b i.e. methyl-(Z)-3-(4-chlorophenyl)-2-(iodomethyl)acrylate (2.0 mmol, 0.673 g), bis(2-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4p as yellow solid. Mp: 74 °C; yield: 0.595 g, 75%; ¹H NMR (400 MHz, CDCl₃): δ 3.80 (s, 3H), 3.99 (s, 2H), 7.03 (t, J = 7.2 Hz, 1H), 7.19 (t, J = 7.6 Hz, 1H), 7.26–7.38 (m, 5H), 7.50 (d, J = 8.0 Hz, 1H), 7.72 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 31.4, 52.5, 125.4, 127.7, 127.922, 127.928, 129.03, 130.9, 131.0, 133.0, 133.1, 135.2, 136.9, 141.0, 167.2; HRMS (ESI) exact mass calcd for C₁₇H₁₄BrClO₂S + K (M + K), 434.9223; found: 434.9214.

Methyl-(Z)-2-((benzylthio)methyl)-3-phenylacrylate (4s). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), dibenzyl disulfide (2.0 mmol, 0.492 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4s as pale yellow liquid. Yield: 0.417 g, 70%; ¹H NMR (400 MHz, CDCl₃): δ 3.46 (s, 2H), 3.64 (s, 2H), 3.72 (s, 3H), 7.10–7.16 (m, 5H), 7.21–7.22 (m, 3H), 7.28–7.30 (m, 2H), 7.63 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 28.5, 37.4, 52.3, 127.0, 128.5, 128.7, 129.0, 129.1, 129.8, 134.9, 138.3, 140.8, 168.0; HRMS (ESI) exact mass calcd for C₁₈H₁₈O₂S + Na (M + Na), 321.0925; found: 321.0920.

Methyl-(Z)-2-((benzylthio)methyl)-3-(4-chlorophenyl)acrylate (4t). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1b i.e. methyl-(Z)-3-(4-chlorophenyl)-2-(iodomethyl)acrylate (2.0 mmol, 0.673 g), dibenzyl disulfide (2.0 mmol, 0.492 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4t as pale yellow liquid. Yield: 0.493 g, 74%; ¹H NMR (400 MHz, CDCl₃): δ 3.52 (s, 2H), 3.74 (s, 2H), 3.82 (s, 3H), 7.22–7.32 (m, 9H), 7.65 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 28.3, 37.4, 52.4, 127.1, 128.5, 128.94, 128.99, 129.0, 129.5, 131.0, 133.2, 135.0, 138.1, 139.5, 167.7; HRMS (ESI) exact mass calcd for C₁₈H₁₇ClO₂S + Na (M + Na), 355.0535; found: 355.0529.

Methyl-(Z)-2-((methylthio)methyl)-3-phenylacrylate (4u)¹³. The title compound was prepared following the general procedure for Table 2, using allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g), dimethyl disulfide (2.0 mmol, 0.188 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4u as colourless oil. Yield: 0.293 g, 66%; ¹H NMR (400 MHz, CDCl₃): δ 2.01 (s, 3H), 3.55 (s, 2H), 3.76 (s, 3H), 7.25–7.34 (m, 3H), 7.40 (d, J = 7.6 Hz, 2H), 7.68 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 16.1, 30.4, 52.2, 128.6, 128.8, 129.3, 129.5, 134.9, 140.6, 167.9.

Methyl-(Z)-2-((methylthio)methyl)-3-(p-tolyl)acrylate (4v). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1c i.e. methyl-(Z)-2-(iodomethyl)-3-(p-tolyl)acrylate (2.0 mmol, 0.632 g), dimethyl disulfide (2.0 mmol, 0.188 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4v as colourless oil. Yield: 0.297 g, 63%; ¹H NMR (400 MHz, CDCl₃): δ 2.09 (s, 3H), 2.35 (s, 3H), 3.63 (s, 2H), 3.82 (s, 3H), 7.19 (d, J = 8.0 Hz, 2H), 7.38 (d, J = 8.0 Hz, 2H), 7.72 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 16.1, 21.3, 30.5, 52.1, 128.3, 129.3, 129.6, 132.0, 139.0, 140.7, 168.0; HRMS (ESI) exact mass calcd for C₁₃H₁₆O₂S + K (M + K), 275.0508; found: 275.0501.

Methyl-(E)-4-methyl-2-((phenylthio)methyl)pent-2-enoate (4w). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1d i.e. methyl-(E)-2-(iodomethyl)-4-methylpent-2-enoate (2.0 mmol, 0.536 g), diphenyl disulfide (2.0 mmol, 0.436 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4w as pale yellow liquid. Yield: 0.360 g, 72%; ¹H NMR (400 MHz, CDCl₃): δ 0.84 (s, 3H), 0.85 (s, 3H), 2.39–2.45 (m, 1H), 3.71 (s, 3H), 3.79 (s, 2H), 6.60 (d, J = 10.4 Hz, 1H), 7.18–7.26 (m, 3H), 739–7.41 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 19.1, 22.1, 28.4, 31.4, 52.0, 125.9, 127.1, 128.8, 128.9, 131.9, 135.9, 152.0, 167.4; HRMS (ESI) exact mass calcd for C₁₄H₁₈O₂S + Na (M + Na), 273.0925; found: 273.0920.

Methyl-(E)-2-(((4-chlorophenyl)thio)methyl)-4-methylpent-2-enoate (4x). The title compound was prepared following the general procedure for Table 2, using allyl iodide 1d i.e. methyl-(E)-2-(iodomethyl)-4-methylpent-2-enoate (2.0 mmol, 0.536 g), bis(3-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 4x as pale yellow liquid. Yield: 0.398 g, 70%; ¹H NMR (400 MHz, CDCl₃): δ 0.87 (s, 3H), 0.88 (s, 3H), 2.39–2.45 (m, 1H), 3.72 (s, 3H), 3.76 (s, 2H), 6.62 (d, J = 10.4 Hz, 1H), 7.22 (dd, J = 8.4 Hz & 2.0 Hz, 2H), 7.32 (dd, J = 8.4 Hz & 2.0 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 22.1, 28.4, 31.6, 52.0, 125.6, 128.9, 133.2, 134.4, 152.3, 167.2; HRMS (ESI) exact mass calcd for C₁₄H₁₇ClO₂S + Na (M + Na), 307.0535; found: 307.0539.

General procedure for Table 3

To a stirred solution of allyl bromide 5 (2.0 mmol) and disulfide (2.0 mmol) in CH₃CN (2.0 mL) was added DTBP (10.0 mmol), then the reaction mixture was stirred for 48 h at 80 °C under nitrogen atmosphere. The solvent was then removed under reduced pressure and the crude product thus obtained was purified by column chromatography (silica gel, 1% EtOAc in hexanes) to provide the allyl thioether 6.

(E)-3-Phenyl-2-((phenylthio)methyl)acrylonitrile (6a)^10c. The title compound was prepared following the general procedure for Table 3, using allyl iodide 5a i.e. (E)-2-(iodomethyl)-3-phenylacrylonitrile (2.0 mmol, 0.538 g), diphenyl disulfide (2.0 mmol, 0.436 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6a as pale yellow liquid. Yield: 0.426 g, 85%; ¹H NMR (400 MHz, CDCl₃): δ 3.73 (s, 2H), 6.65 (s, 1H), 7.27–7.35 (m, 6H), 7.44–7.46 (m, 2H), 7.58–7.59 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 41.1, 107.7, 118.2, 128.1, 128.8, 128.9, 129.3, 130.5, 132.9, 133.1, 133.5, 144.9.

Table 3 DTBP-promoted C–S bond formation between allyl iodides 5 and disulfides 2^a,b

a Reaction conditions: allyl iodide 5 (2.0 mmol), disulfide 2 (2.0 mmol) and DTBP (10.0 mmol) were reacted in CH3CN (2.0 mL) at 80 °C for 48 h.b Isolated yields are based on allyl iodide 5.

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(E)-2-(((4-Chlorophenyl)thio)methyl)-3-phenylacrylonitrile (6b). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5a i.e. (E)-2-(iodomethyl)-3-phenylacrylonitrile (2.0 mmol, 0.538 g), bis(4-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6b as pale yellow liquid. Yield: 0.433 g, 76%; ¹H NMR (400 MHz, CDCl₃): δ 3.71 (s, 2H), 6.68 (s, 1H), 7.24 (dd, J = 8.8 Hz & 2.0 Hz, 2H), 7.35–7.37 (m, 5H; multiplet conations one doublet at δ 7.36, J = 8.4 Hz, 2H and multiplet for 3H), 7.58–7.61 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 41.2, 107.5, 118.0, 128.8, 128.9, 129.4, 130.7, 132.0, 132.9, 134.2, 134.3, 145.1, HRMS (ESI) exact mass calcd for C₁₆H₁₂ClNS + Na (M + Na), 308.0277; found: 308.0092.

(E)-2-(((4-Bromophenyl)thio)methyl)-3-phenylacrylonitrile (6c). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5a i.e. (E)-2-(iodomethyl)-3-phenylacrylonitrile (2.0 mmol, 0.538 g), bis(4-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6c as yellow solid. Mp: 83 °C; yield: 0.475 g, 72%; ¹H NMR (400 MHz, CDCl₃): δ 3.72 (s, 2H), 6.70 (s, 1H), 7.28 (d, J = 8.4 Hz, 2H), 7.36–7.40 (m, 5H, multiplet contains one doublet at δ 7.37, J = 8.4 Hz, 2H and one multiplet for 3H), 7.59–7.61 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 41.0, 107.4, 118.0, 122.3, 128.8, 129.0, 130.7, 132.3, 132.7, 132.9, 134.3, 145.1; HRMS (ESI) exact mass calcd for C₁₆H₁₂BrNS + Na (M + Na), 351.9772; found: 351.9749.

(E)-2-(((4-Methoxyphenyl)thio)methyl)-3-phenylacrylonitrile (6d). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5a i.e. (E)-2-(iodomethyl)-3-phenylacrylonitrile (2.0 mmol, 0.538 g), bis(4-methoxyphenyl)disulfide (2.0 mmol, 0.556 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6d as pale yellow liquid. Yield: 0.488 g, 87%; ¹H NMR (400 MHz, CDCl₃): δ 3.60 (s, 2H), 3.71 (s, 3H), 6.47 (s, 1H), 6.79 (d, J = 8.8 Hz, 2H), 7.32–7.34 (m, 3H), 7.38 (d, J = 8.8 Hz, 2H), 7.53–7.55 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 42.7, 55.4, 108.0, 114.8, 118.2, 123.5, 128.7, 128.9, 130.4, 133.1, 136.3, 144.7, 160.1; HRMS (ESI) exact mass calcd for C₁₇H₁₅NOS + K (M + K), 320.0511; found: 320.0517.

(E)-2-(((3-Chlorophenyl)thio)methyl)-3-phenylacrylonitrile (6e). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5a i.e. (E)-2-(iodomethyl)-3-phenylacrylonitrile (2.0 mmol, 0.538 g), bis(3-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6e as pale yellow liquid. Yield: 0.502 g, 88%; ¹H NMR (400 MHz, CDCl₃): δ 3.75 (s, 2H), 6.76 (s, 1H), 7.07–7.22 (m, 2H), 7.24–7.44 (m, 5H), 7.55–7.65 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 40.5, 107.2, 118.0, 128.0, 128.9, 129.0, 130.2, 130.3, 130.7, 131.7, 132.9, 134.8, 135.7, 145.3; HRMS (ESI) exact mass calcd for C₁₆H₁₂ClNS + Na (M + Na), 308.0277; found: 308.0091.

(E)-2-(((3-Bromophenyl)thio)methyl)-3-phenylacrylonitrile (6f). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5a i.e. (E)-2-(iodomethyl)-3-phenylacrylonitrile (2.0 mmol, 0.538 g), bis(3-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6f as pale yellow liquid. Yield: 0.587 g, 89%; ¹H NMR (400 MHz, CDCl₃): δ 3.74 (s, 2H), 6.76 (s, 1H), 7.11 (t, J = 8.0 Hz, 1H), 7.21–7.41 (m, 5H), 7.56 (s, 1H), 7.61–7.66 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 40.6, 107.2, 118.0, 122.9, 128.9, 129.05, 129.06, 130.7, 130.8, 130.9, 132.9, 134.5, 136.1, 145.4; HRMS (ESI) exact mass calcd for C₁₆H₁₂BrNS + Na (M + Na), 351.9772; found: 351.9625.

(E)-2-(((2-Bromophenyl)thio)methyl)-3-phenylacrylonitrile (6g). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5a i.e. (E)-2-(iodomethyl)-3-phenylacrylonitrile (2.0 mmol, 0.538 g), bis(2-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6g as yellow solid. Mp: 79 °C; yield: 0.574 g, 87%; ¹H NMR (400 MHz, CDCl₃): δ 3.81 (s, 2H), 6.74 (s, 1H), 7.10 (td, J = 7.6 Hz & 1.6 Hz, 1H), 7.21 (td, J = 7.6 Hz & 1.2 Hz, 1H), 7.31–7.37 (m, 3H), 7.45 (dd, J = 8.0 Hz & 1.6 Hz, 2H), 7.53–7.62 (m, 3H); ¹³C NMR (100 MHz, CDCl₃): δ 39.5, 106.8, 118.1, 127.3, 128.2, 128.8, 128.9, 129.3, 130.7, 133.0, 133.5, 133.6, 134.5, 145.4; HRMS (ESI) exact mass calcd for C₁₆H₁₂BrNS + Na (M + Na), 351.9772; found: 351.9713.

(E)-2-((Phenylthio)methyl)-3-(p-tolyl)acrylonitrile (6h)^10c. The title compound was prepared following the general procedure for Table 3, using allyl iodide 5b i.e. (E)-2-(iodomethyl)-3-(p-tolyl)acrylonitrile (2.0 mmol, 0.566 g), diphenyl disulfide (2.0 mmol, 0436 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6h as pale yellow liquid. Yield: 0.482 g, 91%; ¹H NMR (400 MHz, CDCl₃): δ 2.33 (s, 3H), 3.71 (s, 2H), 6.63 (s, 1H), 7.14 (d, J = 8.0 Hz, 2H), 7.26–7.29 (m, 3H), 7.44 (d, J = 8.0 Hz, 2H), 7.52 (d, J = 8.0 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 21.6, 41.1, 106.3, 118.4, 128.0, 128.9, 129.3, 129.6, 130.4, 132.8, 133.7, 141.0, 144.9.

(E)-2-(((4-Chlorophenyl)thio)methyl)-3-(p-tolyl)acrylonitrile (6i). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5b i.e. (E)-2-(iodomethyl)-3-(p-tolyl)acrylonitrile (2.0 mmol, 0.566 g), bis(4-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6i as yellow solid. Mp: 73 °C; yield: 0.551 g, 92%; ¹H NMR (400 MHz, CDCl₃): δ 2.35 (s, 3H), 3.71 (s, 2H), 6.65 (s, 1H), 7.17 (d, J = 8.0 Hz, 2H), 7.24 (d, J = 8.4 Hz, 2H), 7.36 (d, J = 8.8 Hz, 2H), 7.52 (d, J = 8.4 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 22.7, 41.3, 106.1, 118.1, 128.8, 129.3, 129.6, 130.2, 132.1, 134.20, 134.29, 141.2, 145.0; HRMS (ESI) exact mass calcd for C₁₇H₁₄ClNS + K (M + K), 338.0173; found: 338.0179.

(E)-2-(((3-Chlorophenyl)thio)methyl)-3-(p-tolyl)acrylonitrile (6j). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5b i.e. (E)-2-(iodomethyl)-3-(p-tolyl)acrylonitrile (2.0 mmol, 0.566 g), bis(3-chlorophenyl)disulfide (2.0 mmol, 0.574 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6j as yellow solid. Mp: 70 °C; yield: 0.539 g, 90%; ¹H NMR (400 MHz, CDCl₃): δ 2.31 (s, 3H), 3.74 (s, 2H), 6.75 (s, 1H), 7.13 (d, J = 7.6 Hz, 2H), 7.16–7.17 (m, 2H), 7.22–7.31 (m, 1H), 7.39 (s, 1H), 7.46–7.56 (m, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 21.6, 40.5, 105.8, 118.3, 127.8, 128.9, 129.7, 130.0, 130.2, 130.3, 131.4, 134.7, 136.0, 141.2, 145.4; HRMS (ESI) exact mass calcd for C₁₇H₁₄ClNS + Na (M + Na), 322.0433; found: 322.0439.

(E)-2-(((3-Bromophenyl)thio)methyl)-3-(p-tolyl)acrylonitrile (6k). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5b i.e. (E)-2-(iodomethyl)-3-(p-tolyl)acrylonitrile (2.0 mmol, 0.566 g), bis(3-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6k as yellow solid. Mp: 79 °C; yield: 0.605 g, 88%; ¹H NMR (400 MHz, CDCl₃): δ 2.35 (s, 3H), 3.75 (s, 2H), 6.73 (s, 1H), 7.10–7.20 (m, 3H), 7.30–7.39 (m, 2H), 7.52–7.58 (m, 3H); ¹³C NMR (100 MHz, CDCl₃): δ 21.6, 40.7, 105.8, 118.2, 122.8, 128.9, 129.7, 130.1, 130.5, 130.7, 130.8, 134.5, 136.1, 141.3, 145.4; HRMS (ESI) exact mass calcd for C₁₇H₁₄BrNS + K (M + K), 381.9667; found: 381.9666.

(E)-2-(((2-Bromophenyl)thio)methyl)-3-(p-tolyl)acrylonitrile (6l). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5b i.e. (E)-2-(iodomethyl)-3-(p-tolyl)acrylonitrile (2.0 mmol, 0.566 g), bis(2-bromophenyl)disulfide (2.0 mmol, 0.752 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6l as yellow solid. Mp: 69 °C; yield: 0.537 g, 78%; ¹H NMR (400 MHz, CDCl₃): δ 2.34 (s, 3H), 3.80 (s, 2H), 6.71 (s, 1H), 7.10 (td, J = 7.6 Hz & 1.6 Hz, 1H), 7.15 (d, J = 8.0 Hz, 2H), 7.21 (td, J = 7.6 Hz, & 1.2 Hz, 1H), 7.43 (dd, J = 8.0 Hz & 1.6 Hz, 1H), 7.49 (d, J = 8.0 Hz, 2H), 7.58 (dd, J = 8.0 Hz & 1.6 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 21.6, 39.5, 105.5, 118.3, 127.5, 128.1, 128.8, 129.3, 129.6, 130.2, 133.4, 133.9, 141.2, 145.4; HRMS (ESI) exact mass calcd for C₁₇H₁₄BrNS + K (M + K), 381.9667; found: 381.9673.

(E)-2-((benzylthio)methyl)-3-(p-tolyl)acrylonitrile (6m). The title compound was prepared following the general procedure for Table 3, using allyl iodide 5b i.e. (E)-2-(iodomethyl)-3-(p-tolyl)acrylonitrile (2.0 mmol, 0.566 g), dibenzyl disulfide (2.0 mmol, 0.492 g), DTBP (10 mmol, 1.46 g, 1.8 mL) and CH₃CN (2.0 mL), providing 6m as yellow liquid; yield: 0.441 g, 79%; ¹H NMR (400 MHz, CDCl₃): δ 2.40 (s, 3H), 3.31 (s, 2H), 3.76 (s, 2H), 6.83 (s, 1H), 7.24 (d, J = 8.0 Hz, 2H), 7.31–7.35 (m, 5H), 7.67 (d, J = 8.0 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃): δ 21.6, 35.4, 36.2, 106.7, 118.5, 127.4, 128.8, 129.0, 129.1, 129.7, 130.3, 137.2, 141.2, 144.6; HRMS (ESI) exact mass calcd for C₁₈H₁₇NS + K (M + K), 318.0719; found: 318.0726.

Methyl (E)-3-phenyl-2-(((2,2,6,6-tetramethylpiperidin-1-yl)oxy)methyl)acrylate (7). To a stirred solution of allyl iodide 1a i.e. methyl-(Z)-2-(iodomethyl)-3-phenylacrylate (2.0 mmol, 0.604 g) in CH₃CN (2.0 mL) was added TEMPO (2.0 mmol, 0.312 g) and then the reaction mixture was stirred for 80 °C under nitrogen atmosphere for 48 h. The solvent was then removed under reduced pressure and the crude product thus obtained was purified by column chromatography (silica gel, 1% EtOAc in hexanes) to provide the allyl thioether 7 as pale yellow colour liquid. Yield: 0.543 g, 82%; ¹H NMR (400 MHz, CDCl₃): δ 1.06 (s, 6H), 1.09 (s, 6H), 1.40–1.42 (m, 6H), 3.82 (s, 3H), 4.67 (s, 2H), 7.34–7.68 (m, 3H), 7.47–7.49 (m, 2H), 7.83 (s, 1H); ¹³C NMR (100 MHz, CDCl₃): δ 17.1, 20.2, 32.9, 40.0, 52.0, 59.9, 70.8, 128.3, 128.9, 129.5, 135.1, 143.6, 168.5; HRMS (ESI) exact mass calcd for C₂₀H₂₉NO₃ + K (M + K), 370.1785; found: 370.1778.

Acknowledgements

SERB-DST, New Delhi (YSS/2015/001870) and UGC-India (Start-up grant) are gratefully acknowledged for financial support. P. S. and R. C. thanks the UGC and R. B. thanks the SERB-DST for their fellowships. S. S. B. is DST INSPIRE Faculty (IFA-2014/CH-167), DST-India. We thank MRC-MNIT Jaipur for NMR and USIC University of Rajasthan, Jaipur for HRMS & GCMS data collection.

Notes and references

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c7ra04817c

‡ Authors contributed equally.

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