Iodine/Sulfinates: Rapid and Convenient Thiolation of Imidazo Heterocycles without Additives

Abstract

An unprecedented I₂/sulfinate thiolating system is described for the sulfenylation of electron-rich heterocycles. This phosphine-free strategy permits simple, efficient, and fast sulfenylation of imidazo heterocycles, anilines, indoles, coumarins, or enaminones.

Key words

sulfinate - sulfenylation - iodine - microwave heating - heterocycles - thiolation

• References and Notes

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• 10 Thio Ethers 3a–s: General Procedure The appropriate sodium sulfinate 2 (3 equiv) and I₂ (1 equiv) were added to a solution of the heterocycle 1 (1 equiv) in DMF (1 mL) in a microwave vial. The vial was sealed and the mixture was heated at 120 °C by microwave irradiation for 2 h. The solution was then treated with sat. aq Na₂S₂O₃ (10 mL) and the aqueous phase was extracted with EtOAc (3 × 15 mL). The combined organic layers were dried (Na₂SO₄), filtered, and concentrated under a vacuum. 2-Phenyl-3-(phenylsulfanyl)imidazo[1,2-a]pyridine (3a) White solid; yield: 262 mg (87%); mp 110 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.27–8.29 (m, 1 H), 8.20–8.22 (m, 2 H), 7.75 (d, 1 H), 7.42–7.46 (m, 2 H), 7.33–7.40 (m, 2 H), 7.20–7.23 (m, 2 H), 7.12–7.16 (m, 1 H), 6.99–7.02 (m, 2 H), 6.86–6.90 (m, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 151.4, 147.2, 135.3, 133.3, 129.6 (2 CH), 128.8, 128.6 (2 CH), 128.5 (2 CH), 126.9, 126.2, 125.7 (2 CH), 124.7, 117.8, 113.3, 106.5, 106.7.