Green Aerobic Oxidation of Thiols to Disulfides by Flavin–Iodine Coupled Organocatalysis

Abstract

Coupled catalysis using a riboflavin-derived organocatalyst and molecular iodine successfully promoted the aerobic oxidation of thiols to disulfides under metal-free mild conditions. The activation of molecular oxygen occurred smoothly at room temperature through the transfer of electrons from the iodine catalyst to the biomimetic flavin catalyst, forming the basis for a green oxidative synthesis of disulfides from thiols.

Key words

oxidation - thiols - disulfides - flavins - organocatalysis - green chemistry

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• 24 Dioctyl Disulfide (3a): Typical Procedure A mixture of octane-1-thiol (2a; 73.1 mg, 0.50 mmol), flavin 1a (13.6 mg, 0.025 mmol), I₂ (6.35 mg, 0.025 mmol), and t-BuOH (1.0 mL) was stirred at 26 °C (water bath) for 8 h under air (1 atm, balloon) in the dark. The solvent was then evaporated and the residue was purified by column chromatography (silica gel, CHCl₃) to give a colorless oil: yield: 70.7 mg (97%). ¹H NMR (500 MHz, CDCl₃, 25 °C): δ = 2.68 (t, J = 7.4 Hz, 4 H), 1.67 (quin, J = 7.4 Hz, 4 H), 1.41–1.33 (m, 4 H), 1.32–1.20 (m, 16 H), 0.88 (t, J = 6.9 Hz, 6 H). ¹³C{¹H} NMR (126 MHz, CDCl₃, 25 °C): δ = 39.3, 31.8, 29.3, 28.6, 22.7, 14.1.