Tandem asymmetric Aza-Darzens/ring-opening reactions: dual functionality from the silane lewis acid.

The addition of a stabilized sulfur ylide (generated by the rhodium-catalyzed reaction of Ph(2)S with ethyl diazoacetate) to N-acylhydrazones promoted by a chiral silane Lewis acid leads to the highly diastereo- and enantioselective synthesis of beta-chloro-alpha-hydrazido esters. The addition of electron-rich arenes and ZnCl(2) to the reaction mixture leads to the highly diastereo- and enantioselective one-pot synthesis of diarylalanine derivatives. In both cases, the silane Lewis acid responsible for the first reaction performs the second function of activating the aziridine intermediate toward nucleophilic attack.