Catalytic Asymmetric Synthesis of Disubstituted Azetidines

Significance

Masson, Zhu and colleagues report a catalytic asymmetric formal [2+2] cycloaddition between N-sulfonylimines 1 and allenoates 2. The resulting azetidines 3 were obtained in moderate to good yields and with excellent enantioselectivity. Cinchona alkaloid derived catalyst 4 was found to be optimal, and selectively catalyzed the formation of the desired cycloadduct 3 over the aza-Morita-Baylis-Hillman product 5 under optimized conditions. The authors propose a reaction mechanism which accounts for both products via two competitive pathways A and B.