Temperature-Controlled Chemoselective Couplings of Alkyl Halides with Disulfides

An unprecedented, transition metal-free S-alkylation of disulfides with alkyl halides is developed for the first time, providing an efficient and green synthesis of thioethers and even thioesters. Notably, this new method allows the full utilization of both sulfur atoms of disulfides under chemical reductant-free conditions and can be easily scaled up in gram scale, showing good practical value. Control experiments suggested that water, unprecedentedly, serves as the terminal reductant of the whole reaction. Moreover, controllable N-alkyl thiopyridones can be readily obtained at a much lower reaction temperature from the same starting materials, suggesting a kinetic control of N-alkylation vs a thermodynamic control of the S-alkylation process may be involved in the reaction. Interestingly, a halo anion-mediated alkyl group migration from N-alkyl thiopyridones to S-alkyl pyridyl thioethers was observed, suggesting that the reaction may undergo a new and novel reaction mechanism.