Enantioselective N‐Heterocyclic Carbene‐Catalyzed Annulations of 2‐Bromoenals with 1,3‐Dicarbonyl Compounds and Enamines <i>via</i> Chiral α,β‐Unsaturated Acylazoliums

Abstract

Abstract The N‐heterocyclic carbene (NHC)‐catalyzed generation of chiral α,β‐unsaturated acylazoliums from 2‐bromoenals followed by their interception with 1,3‐dicarbonyl compounds or enamines, the formal [3+3] annulation reaction, is reported. The reaction results in the enantioselective synthesis of synthetically and medicinally important dihydropyranones and dihydropyridinones, and tolerates a wide range of functional groups. It is noteworthy that the reaction takes place under mild reaction conditions utilizing relatively low catalyst loadings. In addition, based on DFT calculations, a mechanistic scenario involving the attack of the nucleophile from below the plane of the α,β‐unsaturated acylazoliums, and the mode of enantioinduction is presented.