Chiral amine-catalyzed enantioselective cascade aza-ene-type cyclization reactions

A study was conducted to analyze the organocatalytic highly enantioselective cascade anaene-type cyclization reaction. The study is based on a hypothesis that a chiral secondary amine activated enal enabled a nucleophilic attack by enamide to produce intermediate enamine/iminium. The study found that the reaction of trans-4-nitrocinnamaldehyde with enamide and an organic catalyst, depend on the organocatalysts and additives. The study also found that a base additive can activate the enamide through deprotation and catalysis reaction by readily (S)-diphenylprolinol-TMS ether can establish multistep iminium/enamine transformation in one-pot operation. The study also observed that electronic and steric nature of the aryl rings of enals has limited impact on the stereochemical outcome.