Formal Asymmetric Catalytic Thiolation witha Bifunctional Catalyst at a Water-Oil Interface: Synthesis of Benzyl Thiols

The enantioselective conjugated addition of tritylthiol to insitu generated ortho-quinone methides (o-QMs) is catalyzed by an acid-base bifunctional squaramide organocatalyst. The transformation proceeds with high yield (up to 99%) and stereoselectivity (up to 97:3 e.r.) using water as solvent under mild conditions. The catalyst system provides a new strategy for the synthesis of optically active benzyl mercaptans. Control experiments suggested that o-QMs are generated by the tertiary amine moiety of the squaramide organocatalyst and that the water-oil biphase is crucial for achieving high reactivity and stereoselectivity.