Brønsted Acid-Facilitated Thioetherification Cross-Coupling Reactions with Nickel and Visible Light

Transition metal-catalyzed cross-coupling reactions are essential in modern organic synthesis, facilitating the rapid creation of complex molecular structures. Traditionally, these reactions rely heavily on conventional bases, with only a few exceptions reported. Recently, we developed adaptive dynamic homogeneous catalysis (AD-HoC), a method that enables C(sp2)–S cross-couplings without needing traditional ligands, bases, or additives. Given the growing demand for protocols compatible with acidic conditions in metal-catalyzed cross-couplings, we revisited AD-HoC to pioneer acid-facilitated transition metal-catalyzed thioetherification. Our method enables the swift synthesis of thioethers using nickel and visible light, with a substoichiometric amount of Brønsted acid acting as an enabler. NMR kinetic studies indicate that in the absence of acid, the system displays an induction period characteristic of autocatalysis. Introducing the acid as a simple additive eliminates this induction period and significantly accelerates the reaction. Moreover, the protocol has been successfully scaled to gram-level synthesis using continuous flow technology, achieving productivities of over 100 g per hour in a commercially available lab-scale photoreactor. This highlights the method's robustness and scalability, making it a powerful tool for large-scale applications.