Synthesis and properties of five-membered heterocycles containing two exocyclic conjugated double bonds

Heterocyclic compounds containing two exocyclic double bonds are underrepresented in the literature compared with aromatic heterocycles. However, over the past decade, there has been a growing interest among organic chemists, both in Russia and globally, in developing effective methods for the synthesis (or generation) of heterocycles that incorporate two or more exocyclic double bonds. Exocyclic bonds are involved in chemical reactions that yield products of various structural forms, including spirocyclic compounds, condensed heterocycles and indolones featuring a C3 quaternary stereocentre. Among these compounds, compounds with diverse biological activities were identified. Currently available reviews focus on specific types of heterocycles or particular scaffolds, or address catalytic reactions only. This review summarizes and systematizes the literature concerning the synthesis, properties, and biological activities of five-membered heterocycles containing two exocyclic conjugated bonds such as C=C and C=C, C=C and C=N, C=C and C=O, C=O and C=N, and C=C and C=S, with a primary focus on materials published between 2016 and 2025.
The bibliography includes 218 references. Keywords: heterocycles, furans, pyrroles, indoles