Rapid Method for the Ring Expansion of 1,3-Dithiolanes and 1,3-Dithianes with tert-Butyl Hypochlorite

Abstract

A new method for the ring expansion of 1,3-dithiolanes and 1,3-dithianes to dihydro-1,4-dithiins and dihydro-1,4-dithiepines, respectively, using tert-butyl hypochlorite at room temperature is described. The salient features of the protocol include mild reaction conditions, very short reaction time, and high yield.

Key words

tert-butyl hypochlorite - 1,3-dithiolanes - 1,3-dithianes - sulfur-containing rings - ring expansion

References

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18

General Experimental Procedure: To a stirred solution of 1,3-dithiolane/1,3-dithiane (1.0 equiv) in CCl₄ (10 mL) was added tert-butyl hypochlorite (1.05 equiv) dropwise at r.t. under a stream of nitrogen. The reaction mixture was stirred at r.t. until the starting material had been completely consumed (TLC). The reaction mixture was diluted with CH₂Cl₂. The organic layer was washed successively with a 5% solution of sodium thiosulfate (2 × 15 mL), H₂O (2 × 15 mL), and brine (15 mL). The organic layer was dried over Na₂SO₄ and concentrated in vacuo. Purification by silica gel column chromatography (10% EtOAc-hexane) afforded the pure dihydro-1,4-dithiins and dihydro-1,4-dithianes.

19

2-Phenyl-5,6-dihydro-1,4-dithiin (Table [2] , entry 1): white solid; mp 54-55 °C. ¹H NMR (CCl₄, 60 MHz): δ = 3.25-3.34 (m, 4 H), 6.27 (s, 1 H), 7.38-7.53 (m, 5 H). ¹³C NMR (CDCl₃, 125 MHz): δ = 30.29, 32.26, 113.54, 126.36, 127.97, 128.47, 128.62, 129.81. Anal. Calcd for C₁₀H₁₀S₂: C, 61.86; H, 5.15; S, 32.98. Found: C, 61.83; H, 5.12.
3-Methyl-2-phenyl-5,6-dihydro-1,4-dithiin (Table [2] , entry 3): viscous oil. ¹H NMR (CCl₄, 60 MHz): δ = 2.22 (s, 3 H), 3.64 (m, 4 H), 7.68 (m, 5 H). ¹³C NMR (CDCl₃, 125 MHz): δ = 22.49, 29.83, 30.21, 121.14, 124.65, 127.93, 128.27, 129.71, 139.78. MS (70 eV): m/z = 208, 180, 147, 121. Anal. Calcd for C₁₁H₁₂S₂: C, 63.46; H, 5.77; S, 30.77. Found: C, 63.34; H, 5.72.
2-(4-Chlorophenyl)-5,6-dihydro-1,4-dithiin (Table [2] , entry 6): off-white soild; mp 64-65 °C. ¹H NMR (CDCl₃, 60 MHz): δ = 3.18-3.30 (m, 4 H), 6.31 (s, 1 H), 7.14-7.25 (m, 4 H). ¹³C NMR (CDCl₃, 125 MHz): δ = 32.82, 33.65, 121.31, 128.76, 129.84, 131.45, 133.24, 134.79. Anal. Calcd for C₁₀H₉ClS₂: C, 52.50; H, 3.94; Cl, 5.54; S, 28.01. Found: C, 52.43; H, 3.89; Cl, 15.61.
2-(4-Nitrophenyl)-5,6-dihydro-1,4-dithiin (Table [2] , entry 9): yellow solid; mp 139-140 °C. ¹H NMR (CDCl₃, 60 MHz): δ = 3.28-3.57 (m, 4 H), 6.54 (s, 1 H), 7.46-7.61 (d, J = 8.88 Hz, 2 H), 8.09-8.24 (d, J = 8.88 Hz, 2 H). ¹³C NMR (CDCl₃, 125 MHz): δ = 30.79, 32.96, 121.28, 122.79, 123.45, 127.63, 127.68, 144.36. Anal. Calcd for C₁₀H₉NO₂S₂: C, 50.20; H, 3.77; N, 5.86; S, 26.78. Found: C, 50.15; H, 3.71; N, 5.78.
2-(4-Allyloxyphenyl)-5,6-dihydro-1,4-dithiin (Table [2] , entry 10): viscous oil. ¹H NMR (CDCl₃, 60 MHz): δ = 3.13-3.33 (m, 4 H), 4.44-4.52 (m, 2 H), 5.15-5.45 (m, 2 H), 5.72-6.15 (m, 2 H), 6.68-6.82 (d, J = 8.4 Hz, 2 H), 7.19-7.36 (d, J = 8.4 Hz, 2 H). Anal. Calcd for C₁₃H₁₄OS₂: C, 62.40; H, 5.60; S, 25.60. Found: C, 62.32; H, 5.58.