Catalytic Regio- and Enantioselective Proton Migration from Skipped Enynes to Allenes

Chiral allenes are highly valuable as versatile synthetic intermediates and core skeletons of various functional organic molecules. Despite marked recent advances, the straightforward catalytic enantioselective synthesis of hydrocarbon allenes from readily available starting materials without relying on polar functional groups is still very challenging. Here, we report a copper(I)-catalyzed enantioselective proton migration from skipped enynes to allenes as an efficient approach in chiral allene synthesis. With catalyst loading as low as 0.5 mol %, the reaction proceeds smoothly under mild conditions without the need for additional stoichiometric reagents or generation of waste. Novel chiral ligand L6 plays a critical role in furnishing high catalyst activity, promoting regioselective protonation to produce allenes instead of conjugated enynes, and inducing axial chirality of allenes. The multiple roles of the chiral ligand are rationalized by density functional theory calculations.