Substrate‐Controlled Chemo‐/Enantioselective Synthesis of α‐Benzylated Enals and Chiral Cyclopropane‐Fused 2‐Chromanone Derivatives

Abstract Substrate‐controlled cascade reactions between α,β‐unsaturated aldehydes or their analogues and 2,4‐dinitrobenzyl chloride in the presence of a chiral secondary amine as the catalyst and base were developed, to obtain a broad spectrum of α‐benzylated enals and enantioenriched cyclopropane‐fused chroman‐2‐one derivatives. The cyclopropane‐tethered iminium ion clearly served as a key intermediate in these reactions to trigger stereochemical outcomes, one of which was supported by a control experiment. magnified image