Asymmetric Synthesis of Oxa‐Bridged Oxazocines through a Catalytic RhII/ZnII Relay [4+3] Cycloaddition Reaction

Oxa‐bridged oxazocines bearing three chiral carbon centers were synthesized efficiently through a bimetallic catalytic asymmetric tandem reaction of β,γ‐unsaturated α‐ketoesters with diazoimides. The process contained a rhodium‐promoted in situ generation of isomünchnone from diazoimide decomposition, and a 4+3]‐cycloaddition of β,γ‐unsaturated α‐ketoester catalyzed by a chiral N,N′‐dioxide‐Zn^II complex. Ligand‐accelerated catalysis was found, and a possible transition‐state model was proposed to explain the origin of stereoselectivity.