Cinchona Alkaloid Amide Catalyzed Enantioselective Formal [2+2] Cycloadditions of Allenoates and Imines: Synthesis of 2,4‐Disubstituted Azetidines

Abstract

Mix and go: The quinidine amide 1 catalyzed [2+2] cycloaddition between N-sulfonylimines 2 and alkyl 2,3-butadienoates 3 afforded the R-configured azetidines 4 in excellent yields and enantioselectivities (M.S.=molecular sieve). The S enantiomer was obtained when a quinine amide catalyst, the pseudoenantiomer of 1, was used.