English

• 1.   Introduction

  The simultaneous introduction of two different functional groups to the carbon-carbon triple bond of alkynes is a fundamentally important process in organic synthesis, which offers high impetus for developing novel, short and useful methodologies for synthesizing a variety of organic compounds.^[1] In this context, the free-radical-mediated 1, 2-difunctionalization of alkynes has attracted increasing attention because of its mild conditions, high selectivity and convenient work-up, and has become one of the most powerful methodologies for the construction of polysubstituted alkenes.^{[2, 3]} In particular, the iodosulfonylation of alkynes is a particularly useful reaction, because both iodo and sulfonyl groups can further be used for introducing extensions through various known couplings.^[4] Thus, much attention has been paid to develop convenient and selective methods for the construction of β-iodovinyl sulfones. Commonly, (E)-β-iodovinyl sulfones are synthesized by the addition of sodium sulfinate to alkynes in the presence of NaI or KI with stoichiometric amount of Ce(NH₄)₂(NO₃)₆ or PhI(OAc)₂ as oxidant (Scheme 1a).^[5] In 2013, Li and co-workers^[6] reported theiodosulfonylation of alkynes with sulfonylhydrazides and iodine using tert-butyl hydroperoxide (TBHP) as the oxidant (Scheme 1b). In 2013, an efficient synthetic approach for the construction of various (E)-β-iodovinyl sulfones was achieved by Xie and co-workers (Scheme 1c).^[7] Among the very recent report, the group of Reddy developed I₂/TBHP promoted iodosulfonylation of internal alkynes for the synthesis of various multisubstituted α, β-enones (Scheme 1d).^[8] In spite of these progresses, most of them suffer from the harsh reaction conditions or use of excess peroxide. As part of our continuing efforts toward the development of high efficient radical reactions, ^[9] herein we wish to report a facile and efficient synthetic method for the construction of (E)-β-iodovinyl sulfones through selective iodosulfonylation of terminal alkynes with iodine pentoxide and sulfonylhydrazides (Scheme 1e). Compared to previous work, this methodology avoids the use of insecure peroxide, and various synthetically useful β-iodosulfonyl alkenes were obtained in moderate to good yields.

  Figure 1

  

  Figure 1.  Different synthetic approaches to (E)-β-iodovinyl sulfones

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  2.   Results and discussion

  In an initial experiment, we started our investigation by choosing 1.0 equiv. of phenylacetylene (1a) and 2.0 equiv. p-toluenesulfonylhydrazide (2a) as model substrates to optimize the reaction conditions in the presence of I₂O₅ (1.0 equiv.) under 80 ℃ (Table 1). Gratifyingly, when the model reaction was carried out with CH₃CN as solvent, the desired product (E)-β-iodovinyl sulfone (3a) was obtained as a single regio and stereo isomer in 38% yield (Table 1, Entry 1). Inspired by this result, we next tested different solvents, such as N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), toluene, dimethylacetamide (DMAc), 1, 4-dioxane and tetrahydrofuran (THF), and results indicated that the iodosulfonylation occurs well in 1, 4-dioxane giving the product 3a in the best yield (93%, Table 1, Entry 7). Further elaboration of the loading of 2a to 1.5 equiv. or decreasing the reaction temperature proved to be less effective (Table 1, Entries 8, 9).

  Table 1

  

  Table 1.  Optimization of reaction conditions^a

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  Entry	2a/equiv.	Solvent	Yieldb/%
  1	2.0	MeCN	38
  2	2.0	DMF	77
  3	2.0	DMSO	49
  4	2.0	Toluene	74
  5	2.0	DMAc	84
  6	2.0	1, 4-Dioxane	93
  7	2.0	THF	31
  8	1.5	1, 4-Dioxane	63
  9	2.0	1, 4-Dioxane	69c
  a Reaction conditions: 1a (0.5 mmol), 2a, I2O5 (1.0 equiv, 0.5 mmol) and solvent (2.0 mL) at 80 ℃ for 8 h. b Isolated yield based on 1a. c Room temperature.

  After establishing the optimal reaction conditions for this iodosulfonylation, we next explored the scope of the reaction with various alkynes and sulfonylhydrazides, and the results are summarized in Table 2. Firstly, the impact of substitution variation at the phenyl ring of alkynes was investigated. It was found that various functional groups at the phenyl ring were tolerated well under the present reaction conditions affording the products in moderate to good yields (3b~3k). It is worth noting that halogen-substituted substrates (F, Cl, Br) were also tolerated in this reaction (3f, 3g, 3j, 3k), which were suitable for potential further functionalization. However, under the standard conditions, the iodosulfonylation of heterocyclic acetylenes delivered the desired products 3l in trace amount yield. It is noted that a higher yield of 3d and 3l were obtained while using DMAc as solvent. Furthermore, the application of internal alkyne and aliphatic alkyne also successfully underwent this iodosulfonylation and the desired products 3m and 3n were obtained in 27% and 26% yield, respectively. Finally, sulfonylhydrazides with different substituents were investigated to extend the reaction scope. It was found that various para-substituted sulfonylhydrazides such as those bearing H, F, Cl, Br, CF₃ or OMe groups afforded the products 3o~3t in moderate to good yields. 2-Chloro- benzenesulfonohydrazide and naphthalene-2-sulfono-hydrazide could also transform into the corresponding products in 69% and 87% yields, respectively (3u, 3v).

  Table 2

  

  Table 2.  Substrate scope of the reaction^a

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  To demonstrate the synthetic utility of this method, a gram-scale synthesis of (E)-β-iodovinyl sulfone (3a) was conducted in an open flask under standard reaction conditions. This transformation proceeded smoothly to furnish the desired product 3a in 89% yield. No substantial drop in the yield was observed during the gram-scale synthesis.

  According to the above experimental results and previous reports, ^{[6, 8, 10, 11]} a plausible mechanism is proposed in Scheme 2. The overall process can be divided into three steps. In the first step sulfonyl radical is initiated from sulfonylhydrazide with the assistance of I₂O₅, which underwent a single-electron oxidation process.^[12] In the second step, the selective addition of resultant sulfonyl radicals to carbon-carbon triple bonds afford a (E)-carbon-centered radical intermediate (I), which probably results from the steric effect. Finally, the resultant radical intermediate (I) upon capturing molecular iodine affords (E)-β-iodovinyl sulfones (Path A). It is also possible that 3 is formed via the addition of arenesulphonyl iodides, which is generated from the reaction of sulfonyl radicals with I₂ or iodine free radicals, to aryl acetylenes.^[11i]

  Figure 2

  

  Figure 2.  Plausible mechanism

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  3.   Conclusions

  In summary, we have developed an efficientI₂O₅-promoted iodosulfonylation of alkynes for direct synthesis of (E)-β-iodovinyl sulfones. The present protocol employ commercially available sulfonylhydrazides and I₂O₅ as the sulfonyl and iodine sources, respectively. In addition, this coupling reaction exhibits a broad substrate scope and good functional group tolerance, and various synthetically useful (E)-β-iodosulfonyl alkenes were obtained in moderate to good yields. Compared to previous work, this methodology avoids the use of insecure peroxide. Future efforts will focus on the development of othercoupling processes and the investigation of their applications in organic synthesis.

  4.   Experimental section

  4.1   General information

  All commercially available reagents were used withoutfurther purification. Column chromatography was performed on silica gel (200~300 mesh). ¹H NMR and ¹³C NMR spectra were recorded on a 500 MHz spectrometeroperating at 500 and 125 MHz, respectively. Melting points were tested in an X-4B instrument without correcting temperature.

  4.2   General procedure for the synthesis of (E)-β-iodovinyl sulfones

  An oven-dried reaction vessel was charged with alkyne (0.5 mmol), sulfonylhydrazide (1.0 mmol) and I₂O₅ (166.5 mg, 0.5 mmol) in 2 mL of 1, 4-dioxane. The vessel was sealed and heated to 80 ℃ for 8 h. After completion of reaction, the reaction solution was cooled to room temperature and the volatiles were removed under vacuum. The residue was purified by flash column chromatography (petroleum ether/ethyl acetate, V:V=15:1) to afford the desired product 3.

  (E)-1-[(2-Iodo-2-phenylvinyl)sulfonyl]-4-methylbenzene (3a):^{[6, 7, 9, 13]} White solid (178.5 mg, 93%), m.p. 76~77 ℃ (lit.^[6] 77~79 ℃); ¹H NMR (500 MHz, CDCl₃) δ: 7.48 (d, J=8.2 Hz, 2H), 7.39 (s, 1H), 7.35~7.27 (m, 3H), 7.25 (d, J=6.7 Hz, 2H), 7.20 (d, J=8.1 Hz, 2H), 2.40 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 144.6, 141.3, 139.7, 137.3, 129.8, 129.7, 127.9, 127.9, 127.7, 114.3, 21.7.

  (E)-1-[(2-Iodo-2-(p-tolyl)vinyl)sulfonyl]-4-methylben-zene (3b):^[6] White solid (123.4 mg, 62%), m.p. 102~103 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.55~7.50 (m, 2H), 7.33 (s, 1H), 7.24~7.17 (m, 4H), 7.14~7.10 (m, 2H), 2.42 (s, 3H), 2.38 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 144.6, 140.7, 140.2, 137.5, 136.9, 129.7, 128.6, 127.9, 127.8, 114.8, 21.7, 21.5.

  (E)-1-Ethyl-4-(1-iodo-2-tosylvinyl)benzene (3c):^[7] White solid (133.5 mg, 65%), m.p. 84~85 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.45 (d, J=8.2 Hz, 2H), 7.33 (s, 1H), 7.16 (d, J=8.0 Hz, 4H), 7.09 (d, J=8.0 Hz, 2H), 2.64 (q, J=7.6 Hz, 2H), 2.37 (s, 3H), 1.24 (t, J=7.6 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 146.4, 144.5, 140.9, 137.4, 136.9, 129.6, 127.9, 127.9, 127.4, 114.8, 28.8, 21.7, 15.4.

  (E)-1-((2-Iodo-2-(4-methoxyphenyl)vinyl)sulfonyl)-4-methylbenzene (3d):^[6] White solid (62.2 mg, 30%), m.p. 116~117 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.51 (d, J=8.2 Hz, 2H), 7.31 (s, 1H), 7.26 (d, J=8.7 Hz, 2H), 7.21 (d, J=8.0 Hz, 2H), 6.81 (d, J=8.7 Hz, 2H), 3.83 (s, 3H), 2.40 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 160.8, 144.5, 140.3, 137.5, 131.9, 129.9, 129.7, 127.8, 114.9, 113.3, 55.4, 21.7.

  (E)-1-((2-Iodo-2-(4-(pentyloxy)phenyl)vinyl)sulfonyl)-4-methylbenzene (3e): Brown liquid (166.8 mg, 71%); ¹H NMR (500 MHz, CDCl₃) δ: 7.50 (d, J=8.2 Hz, 1H), 7.46~7.34 (m, 1H), 7.30~7.17 (m, 4H), 7.03 (d, J=8.7 Hz, 1H), 6.87~6.66 (m, 3H), 3.95 (dt, J=11.5, 6.4 Hz, 2H), 2.39 (s, 3H), 1.78 (dt, J=10.7, 6.0 Hz, 2H), 1.46~1.37 (m, 4H), 0.94 (t, J=7.1 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 160.5, 140.2, 137.5, 134.6, 131.6, 129.9, 129.6, 127.8, 113.7, 94.4, 68.1, 28.8, 28.2, 22.5, 21.7, 14.1. HRMS (ESI) calcd for C₂₀H₂₄IO₃S (M+H⁺) 471.0491, found 471.0489.

  (E)-1-Fluoro-4-(1-iodo-2-tosylvinyl)benzene (3f):^[6] White solid (122.6 mg, 61%), m.p. 85~86 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.49 (d, J=8.1 Hz, 2H), 7.35 (s, 1H), 7.26~7.20 (m, 4H), 6.98 (t, J=8.5 Hz, 2H), 2.41 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 164.5, 162.0, 144.8, 141.8, 137.4, 135.7 (d, J=3.75 Hz), 130.1 (d, J=6.25 Hz), 128.8 (d, J=236.25 Hz), 115.1 (d, J=27.5 Hz), 112.5, 21.6.

  (E)-1-Chloro-4-(1-iodo-2-tosylvinyl)benzene (3g):^{[6, 7]} White solid (117.1 mg, 56%), m.p. 143~144 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.50 (d, J=8.1 Hz, 2H), 7.34 (s, 1H), 7.29~7.22 (m, 4H), 7.18 (d, J=8.3 Hz, 2H), 2.41 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 144.9, 141.7, 138.1, 137.1, 135.9, 129.8, 129.1, 128.2, 127.9, 112.0, 21.7.

  (E)-1-(1-iodo-2-tosylvinyl)-3-methylbenzene (3h): White solid (171.1 mg, 86%), m.p. 118~119 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.46 (d, J=8.2 Hz, 2H), 7.38 (s, 1H), 7.21~7.16 (m, 3H), 7.09 (dd, J=29.1, 7.5 Hz, 2H), 6.94 (s, 1H), 2.40 (s, 3H), 2.29 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 144.5, 141.3, 139.6, 137.7, 137.4, 130.6, 129.6, 128.0, 127.9, 127.9, 124.8, 114.6, 21.6, 21.3; HRMS (ESI) calcd for C₁₆H₁₆IO₂S (M+H⁺) 398.9916, found 398.9913.

  (E)-1-(1-Iodo-2-tosylvinyl)-3-methoxybenzene (3i): White solid (196.6 mg, 95%), m.p. 87~88 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.47 (d, J=8.1 Hz, 2H), 7.38 (s, 1H), 7.20 (t, J=8.1 Hz, 3H), 6.84 (t, J=9.2 Hz, 2H), 6.66 (s, 1H), 3.76 (s, 3H), 2.40 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 158.8, 144.5, 141.6, 140.7, 137.3, 129.6, 129.0, 127.9, 120.1, 115.9, 113.6, 112.6, 55.3, 21.6; HRMS (ESI) calcd for C₁₆H₁₆IO₃S (M+H⁺) 414.9865, found 414.9864.

  (E)-1-Fluoro-3-(1-iodo-2-tosylvinyl)benzene (3j): White solid (172.8 mg, 86%), m.p. 89~90 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.51 (d, J=8.2 Hz, 2H), 7.38 (s, 1H), 7.33~7.21 (m, 3H), 7.10~6.99 (m, 2H), 6.86 (d, J=9.1 Hz, 1H), 2.42 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 161.7 (d, J=246.3 Hz), 144.9, 142.1, 141.5 (d, J=8.7 Hz), 137.1, 129.8, 129.7 (d, J=7.5 Hz), 127.9, 123.5 (d, J=2.5 Hz), 116.7 (d, J=21.3 Hz), 114.7 (d, J=22.5 Hz), 111.3 (d, J=2.5 Hz), 21.7; HRMS (ESI) calcd for C₁₅H₁₃FIO₂S (M+H⁺) 402.9665, found 402.9661.

  (E)-1-Bromo-3-(1-iodo-2-tosylvinyl)benzene (3k): White solid (206.1 mg, 89%), m.p. 146~147 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.47 (d, J=8.2 Hz, 2H), 7.45~7.41 (m, 2H), 7.22 (dd, J=15.7, 7.9 Hz, 4H), 7.15 (s, 1H), 2.44 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 144.9, 142.6, 141.4, 137.0, 132.6, 130.0, 129.8, 129.5, 127.9, 126.3, 121.8, 111.0, 21.7; HRMS (ESI) calcd for C₁₅H₁₃BrIO₂S (M+H⁺) 462.8864, found 462.8862.

  (E)-2-(1-Iodo-2-tosylvinyl)thiophene (3l):^[6] Brown liquid (60.5 mg, 31%). ¹H NMR (500 MHz, CDCl₃) δ: 7.61 (d, J=8.2 Hz, 2H), 7.56 (d, J=3.6 Hz, 1H), 7.52 (d, J=5.0 Hz, 1H), 7.33 (s, 1H), 7.26 (d, J=8.1 Hz, 2H), 7.07~7.00 (m, 1H), 2.42 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 144.7, 141.2, 141.1, 137.1, 131.5, 130.1, 129.7, 127.8, 127.4, 103.5, 21.7.

  (E)-(1-Iodo-2-tosylethene-1, 2-diyl)dibenzene (3m): White solid (62.1 mg, 27%), m.p. 185~186 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.42~7.32 (m, 8H), 7.29 (d, J=5.4 Hz, 2H), 7.23~7.17 (m, 2H), 7.12 (d, J=8.1 Hz, 2H), 2.39 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 149.1, 144.3, 142.5, 139.4, 136.8, 131.5, 130.3, 129.2, 129.0, 128.6, 128.3, 127.9, 127.4, 118.1, 21.6; HRMS (ESI) calcd for C₂₁H₁₈IO₂S (M+H⁺) 461.0072, found 461.0070.

  (E)-1-[(2-Iodohept-1-en-1-yl)sulfonyl]-4-methylbenzene (3n):^[6] Brown liquid (49.1 mg, 26%). ¹H NMR (500 MHz, CDCl₃) δ: 7.47 (d, J=7.8 Hz, 2H), 7.36 (s, 1H), 7.09 (d, J=7.6 Hz, 2H), 2.65~2.58 (m, 2H), 2.40 (s, 3H), 1.69~1.61 (m, 2H), 1.38 (s, 4H), 0.94 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 144.4, 140.9, 136.9, 129.6, 127.9, 114.9, 35.8, 31.5, 30.9, 22.6, 21.6, 14.1.

  (E)-[1-Iodo-2-(phenylsulfonyl)vinyl]benzene (3o):^[6] Colourless liquid (164.6 mg, 89%). ¹H NMR (500 MHz, CDCl₃) δ: 7.55 (dd, J=18.9, 7.4 Hz, 3H), 7.41~7.35 (m, 3H), 7.28 (dt, J=14.4, 6.9 Hz, 3H), 7.21 (d, J=6.9 Hz, 2H); ¹³C NMR (125 MHz, CDCl₃) δ: 140.1, 139.2, 138.5, 132.5, 128.8, 127.9, 126.9, 126.8, 126.6, 113.7.

  (E)-1-[(2-Iodo-2-phenylvinyl)sulfonyl]-4-methoxyben-zene (3p): White solid (160.1 mg, 80%), m.p. 113~114 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.53~7.47 (m, 2H), 7.39 (s, 1H), 7.35~7.28 (m, 3H), 7.28~7.22 (m, 2H), 6.88~6.83 (m, 2H), 3.85 (s, 3H); ¹³C NMR (125 MHz, CDCl₃) δ: 163.6, 141.7, 139.7, 131.7, 130.1, 129.8, 127.9, 127.7, 114.3, 113.7, 55.7; HRMS (ESI) calcd for C₁₅H₁₄IO₃S (M+H⁺) 400.9708, found 400.9705.

  (E)-1-Fluoro-4-[(2-iodo-2-phenylvinyl)sulfonyl]benzene (3q): White solid (161.1 mg, 83%), m.p. 84~85 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.56 (ddd, J=9.9, 5.0, 2.5 Hz, 2H), 7.42 (s, 1H), 7.36~7.27 (m, 3H), 7.22 (dt, J=6.8, 1.4 Hz, 2H), 7.09~7.01 (m, 2H); ¹³C NMR (125 MHz, CDCl₃) δ: 165.6 (d, J=255 Hz), 141.2, 139.5, 136.2 (d, J=3.75 Hz), 130.7 (d, J=10 Hz), 129.9, 128.1, 127.7, 116.3 (d, J=22.5 Hz), 114.9; HRMS (ESI) calcd for C₁₄H₁₁FIO₂S (M+H⁺) 388.9508, found 388.9504.

  (E)-1-Chloro-4-[(2-iodo-2-phenylvinyl)sulfonyl]ben-zene (3r): White solid (177.7 mg, 88%), m.p. 98~99 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.45 (d, J=8.6 Hz, 2H), 7.38 (s, 1H), 7.34~7.25 (m, 5H), 7.18 (d, J=7.1 Hz, 2H); ¹³C NMR (125 MHz, CDCl₃) δ: 140.9, 140.2, 139.5, 138.7, 130.0, 129.3, 129.3, 128.1, 127.7, 115.3; HRMS (ESI) calcd for C₁₄H₁₁ClIO₂S (M+H⁺) 404.9213, found 404.9210.

  (E)-1-Bromo-4-[(2-iodo-2-phenylvinyl)sulfonyl]ben-zene (3s): White solid (168.1 mg, 75%), m.p. 106~107 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.54~7.49 (m, 2H), 7.40 (dd, J=6.9, 1.8 Hz, 3H), 7.37~7.27 (m, 3H), 7.23~7.19 (m, 2H); ¹³C NMR (125 MHz, CDCl₃) δ: 140.9, 139.5, 139.2, 132.3, 130.0, 129.4, 128.9, 128.1, 127.7, 115.4; HRMS (ESI) calcd for C₁₄H₁₁BrIO₂S (M+ H⁺) 448.8708, found 448.8705.

  (E)-1-[(2-Iodo-2-phenylvinyl)sulfonyl]-4-(trifluoro-methyl)benzene (3t): White solid (168.6 mg, 77%), m.p. 133~134 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.68~7.57 (m, 4H), 7.42 (s, 1H), 7.33~7.28 (m, 1H), 7.27~7.22 (m, 2H), 7.18~7.13 (m, 2H); ¹³C NMR (125 MHz, CDCl₃) δ: 143.7, 140.7, 139.4, 134.9 (q, J=32.5 Hz), 130.1, 128.5, 128.1, 127.6, 125.8 (q, J=3.8 Hz), 123.1 (q, J=272.5 Hz), 116.0; HRMS (ESI) calcd for C₁₅H₁₁F₃IO₂S (M+H⁺) 438.9477, found 438.9475.

  (E)-1-Chloro-2-[(2-iodo-2-phenylvinyl)sulfonyl]benzene (3u): White solid (139.3 mg, 69%); m.p. 87~88 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 7.59 (s, 1H), 7.50~7.38 (m, 3H), 7.23~7.18 (m, 1H), 7.17~7.07 (m, 5H); ¹³C NMR (125 MHz, CDCl₃) δ: 140.4, 139.3, 138.0, 134.3, 132.4, 131.4, 130.8, 129.8, 127.8, 127.4, 126.9, 114.9; HRMS (ESI) calcd for C₁₄H₁₁ClIO₂S (M+H⁺) 404.9213, found 404.9211.

  (E)-2-[(2-Iodo-2-phenylvinyl)sulfonyl]naphthalene (3v): White solid (182.7 mg, 87%)), m.p. 77~78 ℃; ¹H NMR (500 MHz, CDCl₃) δ: 8.00 (s, 1H), 7.81 (dd, J=42.6, 8.4 Hz, 3H), 7.68~7.52 (m, 3H), 7.46 (s, 1H), 7.27~7.14 (m, 5H); ¹³C NMR (125 MHz, CDCl₃) δ: 141.3, 139.5, 136.9, 135.1, 131.9, 130.0, 129.9, 129.4, 129.3, 128.7, 128.6, 127.9, 127.9, 127.7, 127.6, 122.4; HRMS (ESI) calcd for C₁₈H₁₄IO₂S (M+H⁺) 420.9759, found 420.9756.

  Supporting Information    ¹H NMR and ¹³C NMR spectra of the products 3a~3v. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn.

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  Figure 1  Different synthetic approaches to (E)-β-iodovinyl sulfones

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  Figure 2  Plausible mechanism

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  Table 1.  Optimization of reaction conditions^a

  Entry	2a/equiv.	Solvent	Yieldb/%
  1	2.0	MeCN	38
  2	2.0	DMF	77
  3	2.0	DMSO	49
  4	2.0	Toluene	74
  5	2.0	DMAc	84
  6	2.0	1, 4-Dioxane	93
  7	2.0	THF	31
  8	1.5	1, 4-Dioxane	63
  9	2.0	1, 4-Dioxane	69c
  a Reaction conditions: 1a (0.5 mmol), 2a, I2O5 (1.0 equiv, 0.5 mmol) and solvent (2.0 mL) at 80 ℃ for 8 h. b Isolated yield based on 1a. c Room temperature.

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  Table 2.  Substrate scope of the reaction^a

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