Chem. Res. Chin. Univ., 2014, 30(4), 596—600 doi: 10.1007/s40242-014-4061-7

——————————— *Corresponding authors. E-mail: wgcao@staff.shu.edu.cn; mcmills@ohio.edu Received February 27, 2014; accepted March 24, 2014. Supported by the National Natural Science Foundation of China(No.21272152). © Jilin University, The Editorial Department of Chemical Research in Chinese Universities and Springer-Verlag GmbH

Stereoselective Synthesis of Sulfonyl-substituted trans-2,3-Dihydrofuran Derivatives via Reaction of

Arsonium Ylides with α,β-Unsaturated Ketones

CAO Long1, ZHOU Xiaohong1, CHEN Jie1, ZHANG Hui3, DENG Hongmei3, SHAO Min3, McMILLS Mark C.4* and CAO Weiguo1,2*

1. Department of Chemistry, Shanghai University, Shanghai 200444, P. R. China; 2. State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,

Chinese Academy of Sciences, Shanghai 200032, P. R. China; 3. Instrumental Analysis and Research Center, Shanghai University, Shanghai 200444, P. R. China;

4. Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701, USA

Abstract Trans-2,3-dihydrofuran derivatives 3 or 4 substituted with a sulfonyl group were prepared with high che-moselectivity and good yields by [1+4]-addition reaction of α,β-unsaturated ketones 1 with arsonium bromide 2 in CH2Cl2 in the presence of potassium carbonate at room temperature. The structures of the products were characte-rized by IR, MS, 1H NMR, elemental analysis and single crystal X-ray diffraction analysis. A mechanism for the for-mation of products was also proposed. Keywords Stereoselectivity; Dihydrofuran; Arsonium Ylide

1 Introduction

Dihydrofurans are important heterocyclic scaffolds used for the construction of a variety of naturally occurring sub-stances that generally possess a diversity of biological activi-ties[1―4]. Dihydrofuran derivatives substituted with a sulfonyl group have attracted considerable interest recently because of their promising utility as building blocks for a series of valuable spirocyclic compounds[5,6]. For these reasons, the development of new and efficient methods for the synthesis of substituted dihydrofurans remains an area of keen interest[7―15]. To date a number of methods have been devised for the synthesis of dihydrofuran derivatives con- taining sulfonyl groups[16,17].

In 1996, Moorhoff[18] first reported the synthesis of dihy-drofurans by the reaction of arsonium Ylides with α,β-unsaturated ketones. During the same time period, our group reported a similar reaction, but with high chemoselec- tivity and with the formation of a single stereoisomer[19]. Sub-sequently, a series of approaches to dihydrofurans were pub-lished by our group including the stereoselective synthesis of dihydrofurans substituted with a sulfonyl moiety[20―26]. Yang et al.[27,28] utilized an ammonium Ylide in place of an arsonium Ylide and found that the reaction gave high chemical yield, but produced a mixture of the cis and trans isomers.

In this paper, we report the stereoselective synthesis of sulfonyl-substituted trans-2,3-dihydrofurans via the reaction of α,β-unsaturated sulfones with a variety of arsonium Ylides.

2 Experimental

2.1 General Methods

Unless otherwise noted, all the reagents were purchased from commercial sources and used without further purification. Solvents were distilled before use.

Melting points were measured on a WRS-1 melting point apparatus and were uncorrected. 1H and 13C NMR spectra were recorded on a Bruker DRX-300MHz spectrometer with tetra-methyl silane as the internal standard. IR spectra were obtained on an AVATAR370 FTIR spectrometer. Elemental analyses were performed on an Elementar Vario EL-III instrument. Mass spectra were recorded on a Hewlett Packard-5989A mass spec-trometer. X-Ray analysis was performed on a Bruker Smart Apex2 CCD spectrometer. All yields reported in this publica-tion referred to isolated ones of compounds and their purity was determined by 1H NMR.

α,β-Unsaturated sulfone derivatives 1[20] and arsonium bromide 2 were prepared as described in ref.[29].

2.2 General Procedure for the Synthesis of Com-pounds 3 and 4

To a solution of 4-aryl-3-tosyl-but-3-en-2-one(1, 1 mmol) in dichloromethane(12 mL) were added arsonium bromide (2, 2.1 mmol) and K2CO3(4.0 mmol). The mixture was stirred at ambient temperature for some hours as indicated in Table 1.

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After the completion of the reaction[as monitored by thin layer chromography(TLC)], the solid residue was filtered off and the solvent was evaporated under reduced pressure. The residue was purified by column chromatography on silica gel using ethyl acetate/petroleum ether(1:5, volume ratio) as the eluent to provide trans-2,3-dihydrofuran 3 or 4, respectively. Further purification of the solid samples was carried out by recrystallization from ethyl acetate/petroleum ether.

Table 1 Preparation conditions of compounds 3 and 4

Entry Product Ar R Reaction time/h Yield(%)

1 3Aa C6H5 C6H5 7 71 2 3Ab 4-ClC6H4 C6H5 9 76 3 3Ac 4-CH3OC6H4 C6H5 7 71 4 3Ad 2-ClC6H4 C6H5 10 69 5 3Ae 3-ClC6H4 C6H5 10 67 6 3Ba C6H5 CH3O 8 90 7 3Bb 4-ClC6H4 CH3O 9 86 8 3Bc 4-CH3OC6H4 CH3O 8 82 9 3Bd 2-ClC6H4 CH3O 10 85

10 3Be 3-ClC6H4 CH3O 10 80 11 4Ca C6H5 8 88 12 4Cb 4-ClC6H4 9 84 13 4Cc 4-CH3OC6H4 8 83 14 4Cd 2-ClC6H4 10 78 15 4Ce 3-ClC6H4 10 86 16 3Da C6H5 Furyl 9 59 17 3Db 4-ClC6H4 Furyl 9 75 18 3Dc 4-CH3OC6H4 Furyl 9 72 19 3Dd 2-ClC6H4 Furyl 9 88 20 3De 3-ClC6H4 Furyl 9 61 21 3Ea C6H5 Thineyl 9 62 22 3Eb 4-ClC6H4 Thienyl 10 71 23 3Ec 4-CH3OC6H4 Thienyl 10 61 24 3Ed 2-ClC6H4 Thienyl 10 73 25 3Ee 3-ClC6H4 Thienyl 10 83

2-Benzoyl-3-phenyl-4-tosyl-5-methyl-trans-2,3-dihydro- furan(3Aa): m. p. 196.0―196.7 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.31(s, 3H), 2.44(d, J=1.37 Hz, 3H), 4.48(dd, J=4.94, 1.37 Hz, 1H), 5.66(d, J=4.94 Hz, 1H), 6.98―7.78(m, 14H); IR(KBr), /cm–1: 1682, 1632, 1594, 1493, 1313, 1156; MS(EI), m/z(%): 263(37), 262(14), 158(34), 105(100); elemental anal.(%) calcd. for C25H22O4S: C 71.75, H 5.30; found: C 71.76, H 5.28.

2-Benzoyl-3-(4-chlorophenyl)-4-tosyl-5-methyl-trans-2,3-dihydrofuran(3Ab): m. p. 176.7―177.0 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.38(s, 3H), 2.48(d, J=1.37 Hz, 3H), 4.44(dd, J=5.22, 1.37 Hz, 1H), 5.60(d, J=5.22 Hz, 1H), 6.96―7.78(m, 13H); IR(KBr), /cm–1: 1682, 1632, 1594, 1493, 1313, 1156; MS(EI), m/z(%): 452(1), 297(53), 192(20), 105(100); elemental anal.(%) calcd. for C25H21O4SCl: C 66.29, H 4.67; found: C 66.20, H 4.91.

2-Benzoyl-3-(4-methoxyphenyl)-4-tosyl-5-methyl-trans-2,3-dihydrofuran(3Ac): m. p. 144.3―144.9 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.36(s, 3H), 2.48(d, J=1.37 Hz, 3H), 3.81(s, 3H), 4.48(dd, J=4.95, 1.37 Hz, 1H), 5.66(d, J=4.95 Hz, 1H), 6.98―7.78(m, 13H); IR(KBr), /cm–1: 1699, 1639, 1598, 1502, 1302, 1157; MS(EI), m/z(%): 448(1), 293(100), 188(22), 105(70); elemental anal.(%) calcd. for C26H24O5S: C 69.62,

H 5.39; found: C 69.66, H 5.50. 2-Benzoyl-3-(2-chlorophenyl)-4-tosyl-5-methyl-trans-2,3-

dihydrofuran(3Ad): m. p. 192.3―192.5 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.36(s, 3H), 2.44(d, J=1.37 Hz, 3H), 5.02(brs, 1H), 5.63(brs, 1H), 7.04―7.78(m, 13H); IR(KBr), /cm–1: 1683, 1636, 1597, 1492, 1313, 1156; MS(EI), m/z(%): 452(1), 297(52), 192(17), 105(100); elemental anal.(%) calcd. for C25H21O4SCl: C 66.29, H 4.67; found: C 66.36, H 4.33.

2-Benzoyl-3-(3-chlorophenyl)-4-tosyl-5-methyl-trans-2,3-dihydrofuran(3Ae): m. p. 156.7―157.2 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.36(s, 3H), 2.44(d, J=1.38 Hz, 3H), 4.52(dd, J=5.22, 1.38 Hz, 1H), 5.59(d, J=5.22 Hz, 1H), 6.82(s, 1H), 6.97―7.79(m, 12H); IR(KBr), /cm–1: 1682, 1632, 1594, 1493, 1313, 1156; MS(EI), m/z(%): 452(1), 297(61), 192(18), 105(100); elemental anal.(%) calcd. for C25H21O4SCl: C 66.29, H 4.67; found: C 66.27, H 4.54.

2-Methoxycarbonyl-3-phenyl-4-tosyl-5-methyl-trans-2,3- dihydrofuran(3Ba): m. p. 121.1―121.9 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.31(s, 3H), 2.46(d, J=1.37 Hz, 3H), 3.80(s, 3H), 4.49(dd, J=4.94, 1.37 Hz, 1H), 4.82(d, J=4.94 Hz, 1H), 6.99―7.22(m, 9H); IR(KBr), /cm–1: 1754, 1639, 1594, 1492, 1309, 1154; MS(EI), m/z(%): 372(3), 217(100), 158(19), 43(58); elemental anal.(%) calcd. for C20H20O5S: C 64.50, H 5.41; found: C 64.46, H 5.20.

2-Methoxycarbonyl-3-(4-chlorophenyl)-4-tosyl-5-methyl- trans-2,3-dihydrofuran(3Bb): m. p. 106.6―107.5 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.38(s, 3H), 2.46(d, J=1.37 Hz, 3H), 3.80(s, 3H), 4.42(dd, J=5.22, 1.37 Hz, 1H), 4.79(d, J=5.22 Hz, 1H), 6.91―7.28(m, 8H); IR(KBr), /cm–1: 1759, 1635, 1598, 1491, 1316, 1153; MS(EI), m/z(%): 347(1), 253(37), 251(100), 43(59); elemental anal.(%) calcd. for C20H19O5SCl: C 59.04, H 4.67; found: C 59.00, H 4.90.

2-Methoxycarbonyl-3-(4-methoxyphenyl)-4-tosyl-5- methyl-trans-2,3-dihydrofuran(3Bc): m. p. 94.5―94.6 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.35(s, 3H), 2.41(d, J=1.37 Hz, 3H), 3.78(s, 3H), 3.81(s, 3H) 4.41(dd, J=5.22, 1.37 Hz, 1H), 4.79(d, J=5.22 Hz, 1H), 6.62―7.23(m, 8H); IR(KBr), /cm–1: 1754, 1636, 1609, 1150; MS(EI), m/z(%): 402(1), 247(100), 188(15), 43(41); elemental anal.(%) calcd. for C21H22O6S: C 62.67, H 5.51; found: C 62.67, H 5.42.

2-Methoxycarbonyl-3-(2-chlorophenyl)-4-tosyl-5-methyl- trans-2,3-dihydrofuran(3Bd): m. p. 79.3―79.7 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.32(s, 3H), 2.46(d, J=1.37 Hz, 3H), 4.84(s, 3H), 4.93(brs, 1H), 4.99(brs, 1H), 7.02―7.37(m, 8H); IR(KBr), /cm–1: 1759, 1639, 1597, 1443, 1318, 1156; MS(EI), m/z(%): 253(16), 251(45), 192(20), 43(100); elemental anal.(%) calcd. for C20H19O5SCl: C 59.04, H 4.71; found: C 59.02, H 4.58.

2-Methoxycarbonyl-3-(3-chlorophenyl)-4-tosyl-5-methyl- trans-2,3-dihydrofuran(3Be): m. p. 72.7―73.3 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.32(s, 3H), 2.46(d, J=1.09 Hz, 3H), 3.80(s, 3H), 4.42(dd, J=5.22, 1.38 Hz, 1H), 4.78(d, J=5.22 Hz, 1H), 6.75(s, 1H), 6.92―7.22(m, 7H); IR(KBr), /cm–1: 1759, 1638, 1597, 1437, 1314, 1156; MS(EI), m/z(%): 253(36), 251(100), 91(48), 43(55); elemental anal.(%) calcd. for C20H19O5SCl: C 59.04, H 4.71; found C 59.32, H 4.68.

(3-Phenyl-4-tosyl-5-methyl-trans-2,3-dihydrofuran-2-yl)-

598   Chem. Res. Chin. Univ. Vol.30

pent-3-en-2one(4Ca): m. p. 121.6―122.3 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.01(d, J=1.10 Hz, 3H), 2.21(s, 3H), 2.34(s, 3H), 2.44(d, J=1.37 Hz, 3H), 4.16(dd, J=6.32, 1.37 Hz, 1H), 4.80(d, J=6.32 Hz, 1H), 6.08(s, 1H), 6.95―7.20(m, 9H); IR(KBr),

/cm–1: 1754, 1639, 1594, 1492, 1309, 1154; MS(EI), m/z(%): 372(3), 217(100), 158(19), 43(58); elemental anal.(%) calcd. for C23H22O5S: C 67.30, H 5.40; found: C 67.25, H 5.68.

[3-(4-Chlorophenyl)-4-tosyl-5-methyl-trans-2,3-dihydro- furan-2-yl]pent-3-en-2one(4Cb): m. p. 145.2―145.9 °C; 1H NMR(CDCl3, 300 MHz), δ: 1.95(d, J=1.10 Hz, 3H), 2.21(s, 3H), 2.36(s, 3H), 2.48(d, J=1.37 Hz, 3H), 4.11(dd, J=6.32, 1.37 Hz, 1H), 4.72(d, J=6.32 Hz, 1H), 6.08(s, 1H), 6.85―7.25(m, 8H); IR(KBr), /cm–1: 1759, 1635, 1598, 1491, 1316, 1153; MS(EI), m/z(%): 347(1), 253(37), 251(100), 43(59); elemental anal.(%) calcd. for C23H21O5SCl: C 62.09, H 4.76; found: C 62.14, H 4.53.

[3-(4-Methoxyphenyl)-4-tosyl-5-methyl-trans-2,3-di- hydrofuran-2-yl]pent-3-en-2one(4Cc): m. p. 135.1―135.7 °C; 1H NMR(CDCl3, 300 MHz), δ: 1.99(d, J=0.55 Hz, 3H), 2.20(s, 3H), 2.35(s, 3H), 2.45(dd, J=1.37, 0.55 Hz, 3H), 3.75(s, 3H), 4.08(d, J=6.32 Hz, 1H), 4.72(d, J=6.32 Hz, 1H), 6.08(s, 1H), 6.61―7.25(m, 8H); IR(KBr), /cm–1: 1754, 1636, 1609, 1150; MS(EI), m/z(%): 402(1), 247(100), 188(15), 43(41); elemental anal.(%) calcd. for C24H24O6S: C 65.44, H 5.49; found: C 65.49, H 5.27.

[3-(2-Chlorophenyl)-4-tosyl-5-methyl-trans-2,3-dihydro- furan-2-yl]pent-3-en-2one(4Cd): m. p. 134.5―135.2 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.00(d, J=1.10 Hz, 3H), 2.21(s, 3H), 2.32(s, 3H), 2.48(s, 3H), 4.66(brs, 1H), 4.68(brs, 1H), 6.06(s, 1H), 6.96―7.40(m, 8H); IR(KBr), /cm–1: 1759, 1639, 1597, 1443, 1318, 1156; MS(EI), m/z(%): 253(16), 251(45), 192(20), 43(100); elemental anal.(%) calcd. for C23H21O5SC: C 62.09, H 4.76; found: C 62. 15, H 4.55.

[3-(3-Chlorophenyl)-4-tosyl-5-methyl-trans-2,3-dihydro- furan-2-yl]pent-3-en-2one(4Ce): m. p. 78.2―78.6 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.01(d, J=1.10 Hz, 3H), 2.22(s, 3H), 2.35(s, 3H), 2.46(d, J=1.37 Hz, 3H), 4.15(dd, J=6.32, 1.37 Hz, 1H), 4.72(d, J=6.32 Hz, 1H), 6.06(s, 1H), 6.74(s, 1H), 6.92―7.22(m, 7H); IR(KBr), /cm–1: 1759, 1638, 1597, 1437, 1314, 1156; MS(EI), m/z(%): 253(36), 251(100), 91(48), 43(55); elemental anal.(%) calcd. for C23H21O5SCl: C 62.09, H 4.76; found: C 62.13, H 4.46.

2-Furoyl-3-phenyl-4-tosyl-5-methyl-trans-2,3-dihydro- furan(3Da): m. p. 173.3―173.7 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.32(s, 3H), 2.43(d, J=1.37 Hz, 3H), 4.50(dd, J=4.94, 1.37 Hz, 1H), 5.40(d, J=4.94 Hz, 1H), 6.56―7.59(m, 12H); IR(KBr), /cm–1: 1687, 1635, 1592, 1493, 1314, 1156; MS(EI), m/z(%): 253(100), 158(43), 95(99), 91(52); elemental anal.(%) calcd. for C23H20O5S: C 67.63, H 4.94; found: C 67.68, H 4.67.

2-Furoyl-3-(4-chlorophenyl)-4-tosyl-5-methyl-trans-2,3- dihydrofuran(3Db): m. p. 164.7―165.5 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.38(s, 3H), 2.48(d, J=1.37 Hz, 3H), 4.48(dd, J=4.95, 1.37 Hz, 1H), 5.38(d, J=4.95 Hz, 1H), 6.58―7.59(m, 11H); IR(KBr), /cm–1: 1689, 1636, 1592, 1495, 1315, 1156; MS(EI), m/z(%): 288(16), 286(42), 191(12), 95(100); elemental anal.(%) calcd. for C23H19O5SCl: C 62.37, H 4.32; found: C 62.41, H 4.01.

2-Furoyl-3-(4-methoxyphenyl)-4-tosyl-5-methyl-trans- 2,3-dihydrofuran(3Dc): oil; 1H NMR(CDCl3, 300 MHz), δ: 2.36(s, 3H), 2.42(d, J=1.37 Hz, 3H), 3.72(s, 3H), 4.44(dd, J=5.22, 1.37 Hz, 1H), 5.50(d, J=5.22 Hz, 1H), 6.58―7.56(m, 11H); IR(liquid film), /cm–1: 1644, 1632, 1567, 1480, 1300, 1160; MS(EI), m/z(%): 438(3), 283(100), 224(13), 95(100); elemental anal.(%) calcd. for C24H22O6S: C 65.74, H 5.06; found: C 65.70, H 5.32.

2-Furoyl-3-(2-chlorophenyl)-4-tosyl-5-methyl-trans-2,3- dihydrofuran(3Dd): oil; 1H NMR(CDCl3, 300 MHz), δ: 2.38(s, 3H), 2.48(d, J=1.37 Hz, 3H), 5.08(brs, 1H), 5.32(brs, 1H), 6.58―7.59(m, 11H); IR(liquid film), /cm–1: 1687, 1635, 1592, 1462, 1314, 1156; MS(EI), m/z(%): 288(10), 286(32), 192(19), 95(100); elemental anal.(%) calcd. for C23H19O5SCl: C 62.37, H 4.32; found: C 62.42, H 4.01.

2-Furoyl-3-(3-chlorophenyl)-4-tosyl-5-methyl-trans-2,3- dihydrofuran(3De): m. p. 154.9―155.8 °C; 1H NMR(CDCl3, 300 MHz), δ: 2.37(s, 3H), 2.51(d, J=1.37 Hz, 3H), 4.52(dd, J=4.95, 1.37 Hz, 1H), 5.38(d, J=4.95 Hz, 1H), 6.59―7.60(m, 11H); IR(KBr), /cm–1: 1678, 1638, 1596, 1560, 1464, 1155; MS(EI), m/z(%): 288(29), 286(87), 191(20), 95(100); elemental anal.(%) calcd. for C23H19O5SCl: C 62.37, H 4.32; found: C 62.32, H 4.60.

2-Thienoyl-3-phenyl-4-tosyl-5-methyl-trans-2,3-dihydro- furan(3Ea): m. p. 119.8―120.2 °C; 1H NMR(CDCl3, 300Hz), δ: 2.32(s, 3H), 2.48(d, J=1.37 Hz, 3H), 4.59(dd, J=5.22, 1.37 Hz, 1H), 5.42(d, J=5.22 Hz, 1H), 6.96―7.72(m, 12H); IR(KBr),

/cm–1: 1667, 1639, 1597, 1494, 1315, 1156; MS(EI), m/z(%): 253(100), 158(43), 95(99), 91(52); elemental anal.(%) calcd. for C23H20O4S2: C 65.07, H 4.75; found: C 65.11, H 4.98.

2-Thienoyl-3-(4-chlorophenyl)-4-tosyl-5-methyl-trans- 2,3-dihydrofuran(3Eb): m. p. 174.8―175.8 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.38(s, 3H), 2.50(d, J=1.37 Hz, 3H), 4.58(dd, J=5.49, 1.37 Hz, 1H), 5.39(d, J=5.49 Hz, 1H), 6.96―7.76(m, 11H); IR(KBr), /cm–1: 1668, 1639, 1597, 1494, 1315, 1157; MS(EI), m/z(%): 304(27), 302(77), 192(27), 111(100); elemental anal.(%) calcd. for C23H19O4S2Cl: C 60.19, H 4.17; found: C 60.23, H 4.36.

2-Thienoyl-3-(4-methoxyphenyl)-4-tosyl-5-methyl-trans-2,3-dihydrofuran(3Ec): m. p. 144.0―144.7 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.36(s, 3H), 2.48(d, J=1.37 Hz, 3H), 3.80(s, 3H), 4.52(dd, J=5.22, 1.37 Hz, 1H), 5.39(d, J=5.22 Hz, 1H), 6.69―7.74(m, 11H); IR(KBr), /cm–1: 1675, 1638, 1611, 1513, 1319, 1154; MS(EI), m/z(%): 438(3), 283(100), 224(13), 95(100); elemental anal.(%) calcd. for C24H22O5S2: C 63.45, H 4.45; found: C 63.41, H 4.78.

2-Thienoyl-3-(2-chlorophenyl)-4-tosyl-5-methyl-trans- 2,3-dihydrofuran(3Ed): oil; 1H NMR(CDCl3, 300 MHz), δ: 2.35(s, 3H), 2.48(d, J=1.37 Hz, 3H), 5.09(brs, 1H), 5.42(brs, 1H), 7.06―7.72(m, 11H); IR(liquid film), /cm–1: 1714, 1640, 1595, 1482, 1325, 1150; MS(EI), m/z(%): 348(7), 346(18), 192(27), 111(100); elemental anal.(%) calcd. for C23H19O4S2Cl: C 60.19, H 4.17; found: C 60.15, H 4.37.

2-Thienoyl-3-(3-chlorophenyl)-4-tosyl-5-methyl-trans- 2,3-dihydrofuran(3Ee): m. p. 152.4―152.7 °C; 1H NMR (CDCl3, 300 MHz), δ: 2.39(s, 3H), 2.51(d, J=1.37 Hz, 3H), 4.61(dd, J=4.95, 1.37 Hz, 1H), 5.37(d, J=4.95 Hz, 1H), 6.81(s,

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1H), 6.98―7.74(m, 10H); IR(KBr), /cm–1: 1667, 1639, 1597, 1413, 1315, 1157; MS(EI), m/z(%): 304(35), 302(98), 191(25), 111(100); elemental anal.(%) calcd. for C23H19O4S2Cl: C 60.19, H 4.17; found: C 60.26, H 4.36.

3 Results and Discussion A series of α,β-unsaturated ketones bearing a 2-substituted

tosyl group 1 was reacted with a variety of arsonium Ylides derived from arsonium bromide 2 to prepare the 3-tosyl substi-tuted trans-2,3-dihydrofuran derivatives 3 or 4 (Scheme 1, Table 1). Structures of the products were identified by IR, MS, 1H NMR, elemental analysis and single crystal X-ray diffrac-tion analysis(Fig.1, CCDC No.663390).

Scheme 1 Preparation of trans-2,3-dihydrofuran

derivatives

Fig.1 Molecular structure of compound 3Bc The proposed reaction mechanism shown in Scheme 2

accounts for the diastereoselective formation of the trans- substituted dihydrofuran product. In the event, the olefin of the α,β-unsaturated ketone 1 is attacked by the carban ion derived from arsonium bromide to yield an intermediate with two stereogenic atoms C2 and C3, followed by an intramolecular nucleophilic substitution by the enolate oxygen atom. Two possible modes of attack are available to the pendant enolate ion, either syn(II) to the COR or anti(III) when the oxygen atom attack C2 from the backside of leaving group(Ph3As) as in structures II and III in Scheme 2. Intermediate II appears to be more stable than III owing to the relief of steric crowding by the removal of the offending Ar-COR interaction. The preferred reactive conformer II will generate the

trans-dihydrofuran 3. Alternatively, when acetylmethyl triphe-nylarsonium bromide (2C) is reacted with α,β-unsaturated ke-tone 1, dihydrofuran 4 is formed through a subsequent Wittig reaction of arsonium Ylide 2C with dihydrofuran 3.

Scheme 2 Mechanism for the formation of compound 3

4 Conclusions This work provides a simple and practical procedure for

the synthesis of trans-2,3-dihydrofurans with a pendant sul-fonyl group. Moreover, high stereoselectivity along with ex-ceptional chemical yield makes the method a practical one for the preparation of these useful scaffolds.

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