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 Ph2S with ethyl diazoacetate) to N-acylhydrazones promoted by a chiral silane Lewis acid leads to the highly diastereo- and enantioselective synthesis of B-chloro-alpha-hydrazido esters. The addition of electron-rich arenes and ZnCl2 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.