One-pot synthesis of optically active 1,4-disubstituted-3-carbamoyl-azetidinones from 5-[(N-arylamino)(hydroxyl)methylene]-2,2-dimethyl-1,3-dioxa-4,6-diones and chiral aldimines is achieved via thermal generation of carbamoyl ketenes and subsequent [2+2] cycloaddition. Three possible chiral induction approaches were tested and (R)-(+)-1-phenylethylamine was confirmed as the best chiral auxiliary. Among
Ketenes generated during the thermal decomposition of 5-[(N-aryl/alkylamino)(hydroxyl)methylene]-2,2-dimethyl-1,3-dioxa-4,6-diones react with highly electrophilic iminium ions. The initial [2+2] cycloaddition product rearranges to 2-arylidene malonamide. Mechanistic aspects of the process are presented.