Synthesis of Diheteroatomic Five‐Membered Heterocyclic Compounds from α,β‐Unsaturated Aldehydes

The recent increase in interest in the chemistry of azoles has been owing to their paramount importance in several essential fields of research, such as pharmacology, medicine, biology, the organic synthesis of fine chemicals, agricultural chemistry, and the chemical industry. This Focus Review summarizes and highlights recently developed methods for the synthesis of five‐membered N,N‐, N,O‐, and N,S‐heterocycles based on the transformations of 2‐alkenals. Over the last 15 years, these reactions, which often differ from reactions involving other α,β‐unsaturated carbonyl compounds in terms of method and results, have gathered significant momentum. The multitude of catalytic and technological novelties discussed in this Focus Review, such as asymmetric metal‐ and organocatalysis, one‐pot multicomponent reactions that proceed through domino, cascade, or tandem sequences, and microwave activation, promote the formation of a diverse range of target products, the structures of which become clear from the mechanistic schemes given in this Focus Review. The mechanisms discussed reflect great advances in the chemo‐, regio‐, and stereoselectivity of the reactions of 2‐alkenals, which allows new azoles and related compounds (imidazoles, pyrazoles, oxazoles, thiazoles, and their hydrogenated derivatives) to be synthesized.