A Sulfonylation Reaction: Direct Synthesis of 2-Sulfonylindoles from Sulfonyl Hydrazides and Indoles

Abstract

A metal-free synthesis of 2-sulfonylindole derivatives has been developed through a novel TBHP/I₂-mediated coupling of C3/unsubstituted indoles with sulfonyl hydrazides. The reaction utilizes readily available starting materials under mild reaction conditions, providing an alternative and attractive approach to 2-sulfonylindoles with high yields. The developed synthetic procedure is suitable for both N-protected or unprotected indoles.

Key words

direct synthesis - sulfonylation - 2-sulfonylindoles - sulfonyl hydrazides - indoles

• References and Notes

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• 15 General Procedure for the Synthesis of 2-Sulfonylindoles To a mixture of indole 1 (0.5 mmol) with sulfonyl hydrazide 2 (1 mmol), iodine (20 mol%), TBHP (70% in water, 1 mmol) in DCE (2 mL). The resulting reaction mixture was stirred at r.t. for 2 h. Upon completion, distilled deionized H₂O (10 mL) and sat. Na₂S₂O₃ (10 mL) were added, and the mixture was extracted with EtOAc (3 × 20 mL). The combined organic layer was washed with sat. brine (20 mL), dried over anhydrous Na₂SO₄, and concentrated in vacuum. The crude product was purified by column chromatography using EtOAc–hexanes (1:5) as eluent to afford the desired 2-sulfonylindole 3.
• 16 See Supporting Information for detailed experimental procedures and characterization data. 2-(Phenylsulfonyl)-1H-indole (3a)^8a White solid (118.4 mg, 92% yield); mp 159–161 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.81 (br s, 1 H), 8.04 (d, J = 7.0 Hz, 2 H), 7.66 (d, J = 9.0 Hz, 1 H), 7.50 (d, J = 2.5 Hz, 1 H), 7.48 (d, J = 8.0 Hz, 1 H), 7.31 (d, J = 6.0 Hz, 1 H), 7.21–7.17 (m, 3 H), 7.14 (t, J = 7.0 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 141, 136.3, 133.5, 130.5, 128.9, 128.5, 124.6, 122.9, 120.7, 119.5, 111.4, 108.9. Anal. Calcd (%) for C₁₄H₁₁NO₂S: C, 65.35; H, 4.31; N, 5.44. Found: C, 65.37; H, 4.32; N, 5.45. 2-Tosyl-1H-indole (3b) ^8a White solid (122.1 mg, 90% yield); mp 195–197 °C. ¹H NMR (500 MHz, CDCl₃): δ = 9.02 (br s, 1 H), 7.95 (d, J = 8.0 Hz, 2 H), 7.65 (d, J = 7.5 Hz, 1 H), 7.50 (d, J = 2.5 Hz, 1 H), 7.46 (d, J = 8.0 Hz, 1 H), 7.30–7.27 (m, 1 H), 7.20 (t, J = 7.5 Hz, 1 H), 7.20 (d, J = 8.0 Hz, 2 H), 2.33 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 143.7, 136.3, 135.3, 130.2, 139.3, 128.9, 126.1, 122.8, 120.7, 119.5, 111.3, 108.5, 20.7. Anal. Calcd (%) for C₁₅H₁₃NO₂S: C, 66.40; H, 4.83; N, 5.16. Found: C, 66.43; H, 4.81; N, 5.15. 2-[(4-Chlorophenyl)sulfonyl]-1H-indole (3c) ^8a White solid (128.4 mg, 88% yield); mp 146–148 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.82 (br s, 1 H), 7.83 (d, J = 9 Hz, 2 H), 7.75 (d, J = 8.5 Hz, 2 H), 7.59 (d, J = 8.0 Hz, 1 H), 7.49 (d, J = 2.5 Hz, 1 H), 7.46 (d, J = 8.0 Hz, 1 H), 7.30–7.26 (m, 1 H), 7.20–7.17 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 140, 137.6, 136.3, 130.6, 130.4, 128.6, 126.9, 123.1, 120.9, 119.3, 111.5, 109.1. Anal. Calcd (%) for C₁₄H₁₀ClNO₂S: C, 57.63; H, 3.45; N, 4.80. Found: C, 57.65; H, 3.47; N, 4.82. 2-[(4-Bromophenyl)sulfonyl]-1H-indole (3d) ^8a White solid (142.9 mg, 85% yield); mp 191–193 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.87 (br s, 1 H), 7.71 (d, J = 8.5 Hz, 2 H), 7.50 (d, J = 7.5 Hz, 1 H), 7.42 (d, J = 2.5 Hz, 1 H), 7.39 (d, J = 7.5 Hz, 1 H), 7.19–7.18 (m, 3 H), 7.12–7.09 (m, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 140.5, 138.4, 136.3, 131.5, 130.6, 127.2, 123.1, 120.9, 119.3, 118.1, 111.5, 109. Anal. Calcd (%) for C₁₄H₁₀BrNO₂S: C, 50.01; H, 3.00; N, 4.17. Found: C, 50.04; H, 3.01; N, 4.15. 2-[(4-Methoxyphenyl)sulfonyl]-1H-indole (3e) ^8a White solid (127.9 mg, 89% yield); mp 186–187 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.81 (br s, 1 H), 7.9 (d, J = 8.5 Hz, 2 H), 7.42 (d, J = 2.5 Hz, 1 H), 7.31 (d, J = 8.5 Hz, 1 H), 7.09 (d, J = 7.5 Hz, 2 H), 7.06–7.03 (m, 2 H), 6.91 (d, J = 8.5 Hz, 1 H), 3.77 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 162.9, 136.4, 135, 131.2, 129.8, 128.5, 125.5, 124.5, 115, 113.4, 112.3, 108.6, 55.6. Anal. Calcd (%) for C₁₅H₁₃NO₃S: C, 62.70; H, 4.56; N, 4.87. Found: C, 62.72; H, 4.55; N, 4.89. 2-[(4-Fluorophenyl)sulfonyl]-1H-indole (3f) ^8a White solid (112.9 mg, 82% yield); mp 155–157 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.95 (br s, 1 H), 8.03 (d, J = 8.5 Hz, 2 H), 7.57–7.52 (m, 3 H), 7.36 (t, J = 7.0 Hz, 1 H), 7.24 (t, J = 7.5 Hz, 1 H), 7.16 (d, J = 9 Hz, 2 H). ¹³C NMR (125 MHz, CDCl₃): δ = 166 (d, J = 251.6 Hz), 136.4 (d, J = 3 Hz), 135, 130 (d, J = 9.6 Hz), 128.3, 124.9, 123.4, 121.3, 119.1, 116.3 (d, J = 22.6 Hz), 111.8, 109. Anal. Calcd (%) for C₁₄H₁₀FNO₂S: C, 61.08; H, 3.66; N, 5.09. Found: C, 61.05; H, 3.67; N, 5.06. 2-(Naphthalen-2-ylsulfonyl)-1H-indole (3h) ^8a White solid (138.3 mg 90% yield); mp 156–158 °C. ¹H NMR (500 MHz, CDCl₃): δ = 9.05 (br s, 1 H), 8.46 (s, 1 H), 7.96–7.93 (m, 2 H), 7.72 (d, J = 8.0 Hz, 1 H), 7.65–7.61 (m, 2 H), 7.48–7.45 (m, 2 H), 7.38–7.33 (m, 2 H), 7.29–7.25 (m, 2 H), 7.16–7.13 (m, 2 H). ¹³C NMR (125 MHz, CDCl₃): δ = 138.5, 136.4, 133.6, 131.2, 130.5, 128.9, 128.1, 127.5, 126.8, 126.2, 124.9, 124.6, 123.3, 122.9, 120.8, 119.5, 111.4, 108.6. Anal. Calcd (%) for C₁₈H₁₃NO₂S: C, 70.34; H, 4.26; N, 4.56. Found: C, 70.31; H, 4.23; N, 4.57. 2-(Methylsulfonyl)-1H-indole (3i) ^8a White solid (89.8 mg, 92% yield); mp 184–186 °C. ¹H NMR (500 MHz, CDCl₃): δ = 9.01 (br s, 1 H), 7.65 (d, J = 7.5 Hz, 1 H), 7.43 (d, J = 8.0 Hz, 1 H), 7.29–7.25 (m, 1 H), 7.22–7.16 (m, 2 H), 3.25 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 136.4, 133.3, 126.9, 126.2, 122.9, 121, 111.6, 108.2, 45.2. Anal. Calcd (%) for C₉H₉NO₂S: C, 55.37; H, 4.65; N, 7.17. Found: C, 55.40; H, 4.63; N, 7.15. 5-Methoxy-2-(phenylsulfonyl)-1H-indole (3m) ^8a White solid (137.9 mg, 96% yield); mp 135–137 °C. ¹H NMR (400 MHz, CDCl₃): δ = 9.01 (br s, 1 H), 8.02 (d, J = 8.0 Hz, 2 H), 7.57–7.51 (m, 3 H), 7.36 (d, J = 7.6 Hz, 1 H), 7.22 (s, 1 H), 7.16–7.12 (m, 2 H), 3.81 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 155, 140.9, 134.1, 133.5, 132.6, 129.8, 128.1, 127.7, 117.6, 112.3, 109, 102.3, 55.5. Anal. Calcd (%) for C₁₅H₁₃NO₃S: C, 62.70; H, 4.56; N, 4.87. Found: C, 62.67; H, 4.57; N, 4.85. 4-Methyl-2-(phenylsulfonyl)-1H-indole (3n) ^8a White solid (124.8 mg, 92% yield); mp 166–169 °C. ¹H NMR (400 MHz, CDCl₃): δ = 9.01 (br s, 1 H), 7.96 (d, J = 8.4 Hz, 2 H), 7.50–7.45 (m, 3 H), 7.32–7.27 (m, 3 H), 6.96 (d, J = 7.2 Hz, 1 H), 2.51 (s, 3 H). Anal. Calcd (%) for C₁₅H₁₃NO₂S: C, 66.40; H, 4.83; N, 5.16. Found: C, 66.38; H, 4.80; N, 5.17. 6-Chloro-2-(phenylsulfonyl)-1H-indole (3o) ^8a White solid (116.7 mg, 80% yield); mp 181–183 °C. ¹H NMR (500 MHz, CDCl₃): δ = 9.01 (br s, 1 H), 8.01 (d, J = 8.5 Hz, 2 H), 7.55–7.49 (m, 4 H), 7.24 (d, J = 7.5 Hz, 1 H), 7.09–7.06 (m, 2 H). ¹³C NMR (125 MHz, CDCl₃): δ = 141.9, 136.4, 133.9, 129.7, 128.2, 125.9, 124.8, 123.3, 121.2, 119, 111.7, 109. Anal. Calcd (%) for C₁₄H₁₀ClNO₂S: C, 57.63; H, 3.45; N, 4.80. Found: C, 57.61; H, 3.47; N, 4.78. 7-Methyl-2-(phenylsulfonyl)-1H-indole (3p) ¹ White solid (130.2 mg, 96% yield); mp 171–173 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.97 (br s, 1 H), 7.98 (d, J = 8.0 Hz, 2 H), 7.61–7.53 (m, 4 H), 7.20 (s, 1 H), 7.13–7.07 (m, 2 H), 2.50 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 141.1, 136.2, 134.2, 131.8, 130.2, 129.4, 129, 126.2, 122.9, 120.7, 119.6, 111, 19.7. Anal. Calcd (%) for C₁₅H₁₃NO₂S: C, 66.40; H, 4.83; N, 5.16. Found: C, 66.37; H, 4.81; N, 5.15. 3-Methyl-2-(phenylsulfonyl)-1H-indole (3q) ^8d White solid (120.7 mg 89% yield); mp 168–169 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.87 (br s, 1 H), 7.99 (d, J = 7.6 Hz, 2 H), 7.60–7.49 (m, 4 H), 7.43–7.40 (t, J = 7.6 Hz, 2 H), 7.18–7.15 (t, J = 7.6 Hz, 1 H), 2.53 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 141.5, 136.2, 133.5, 129.4, 128.2, 127, 126.1, 122.2, 120.5, 119.6, 112.1, 111.4, 8.8. Anal. Calcd (%) for C₁₅H₁₃NO₂S: C, 66.40; H, 4.83; N, 5.16. Found: C, 66.42; H, 4.80; N, 5.13. 5-Bromo-2-[(4-chlorophenyl)sulfonyl]-1H-indole (3r) ^8b Brown solid (127.8 mg, 69% yield); mp 183−186 °C. ¹H NMR (500 MHz, CDCl₃): δ = 8.85 (br s, 1 H), 8.02 (d, J = 7.0 Hz, 2 H), 7.81 (s, 1 H), 7.59 (d, J = 7.0 Hz, 2 H), 7.46 (d, J = 7.0 Hz, 1 H), 7.43 (d, J = 7.5, 1 H), 7.14 (d, J = 2.0 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 141.1, 140, 137.4, 136.3, 131, 130, 129.2, 129, 126.4, 115.8, 114.3, 108.5. Anal. Calcd (%) for C₁₄H₉BrClNO₂S: C, 45.37; H, 2.45; N, 3.78. Found: C, 45.39; H, 2.44; N, 3.75. S-p-Tolyl-4-methylbenzenesulfonothioate (3aa) ^9f White solid (194.9 mg 70% yield); mp 91–93 °C. ¹H NMR (500 MHz, CDCl₃): δ = 7.49 (d, J = 7.0 Hz, 2 H), 7.22–7.16 (m, 4 H), 7.14 (d, J = 7.0 Hz, 2 H), 2.36 (s, 3 H), 2.32 (s, 3 H). 1,2-Di-p-tolyldisulfane (3ab) ^9f White solid (36.8, mg 15% yield); mp 45–48 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.42 (d, J = 8.0 Hz, 4 H), 7.12 (d, J = 8.0 Hz, 2 H), 2.35 (s, 6 H).