,-Unsaturated Aldehydes in the Synthesis of Five-Membered Heterocyclic Compounds with One Heteroatom: Recent Advances from Developments in Metal- and Organocatalysis

The ever-increasing interest in the chemistry of five-membered heterocyclic compounds is due to their paramount importance in such essential fields as pharmacology, medicine, biology, organic synthesis of fine chemicals, agricultural chemistry, and the chemical industry. This Review summarizes and highlights methods for the synthesis of five-membered O-, N-, and S-heterocycles based on transformations of ,-enals. Over the last decade, these reactions, which often differ from the processes involving other ,-unsaturated carbonyl compounds in methodology and results, have been gathering momentum. Many of the catalytic and technological novelties discussed in the review, such as asymmetric metal- and organocatalysis, multiple catalysts, one-pot multicomponent reactions proceeding through domino, cascade, or tandem reactions, and microwave activation, promote the formation of diverse target products, the structures of which becomes clear from the mechanistic schemes given in the review. The mechanisms discussed reflect great advances in the chemo-, regio-, and stereoselectivity of the reactions with participation of ,-alkenals, achieved in the last 15years, which allows new five-membered heteroarenes and related compounds (pyrroles, dihydropyrroles, pyrrolidines, furans, thiophenes) to be synthesized.