Cinchona Alkaloid-Amides Catalyzed Enantioselective Formal [2+2] Cycloadditions of Allenoates and Imines: Enantioselective Synthesis of 2,4-Substituted Azetidines

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