Cobalt‐Catalyzed Diastereo‐ and Enantioselective Reductive Coupling of Cyclobutenes and Aldimines

A cobalt‐catalyzed protocol for diastereo‐ and enantioselective reductive coupling of unactivated cyclobutenes and aldimines through oxidative cyclization promoted by a chiral bisphosphine–cobalt is presented. Such processes represent an unprecedented reaction pathway for cobalt catalysis that enable umpolung reactivity of cyclobutenes with imines and incorporation of a chiral amino‐containing fragment onto the four‐membered ring scaffold, delivering a broad scope of enantioenriched cyclobutyl amines in up to 98% yield and >99.5:0.5 er as a single diastereomer. Functionalization provided a variety of densely functionalized cyclobutanes that are otherwise difficult to access. Preliminary mechanistic studies revealed that the reaction proceeded through diastereo‐ and enantioselective oxidative cyclization followed by protonation. Density functional theory calculations elucidated the origin of stereoselectivity in detail.