An Unexpected Phosphine-Catalyzed Asymmetric and Stereospecific [3+2] Cyclization for the Construction of Oxetane γ-Spirolactams

Herein, we disclose an unexpected phosphine-catalyzed asymmetric [3+2] cyclization of oxetane MBH carbonates with aryl aldimines. In this process, the MBH carbonate employs its γ-carbon and ester group to participate in the cyclization, affording a series of oxetane γ-spirolactams bearing an exocyclic vinyl ether, in moderate to good yields with moderate to good enantioselectivity. The process exhibits stereospecificity, and controllable synthesis of the E or Z configuration has been achieved.