Synthesis of α-C-Glycoside Conjugates via Giese-like Reaction Triggered by Photoactivated Electron Donor–Acceptor (EDA) Complexes and in situ photocatalytic species

Abstract

Two visible-light-mediated, catalyst-free strategies for the synthesis of α-C-glycoside conjugates are reported. The methods exploit electron donor–acceptor (EDA) complex activation and in situ generated photocatalytically active species to trigger Giese-like radical additions from glycosyl iodide to electron-poor olefins under mild conditions. Iodide derived glycosyl donors participate, enabling the formation of C-glycosidic linkages across a broad range of mono- and disaccharide substrates, dehydroalanine derivatives, and bisphosphonate acceptors. Mechanistic studies indicate that distinct activation pathways operate depending on the reaction conditions: deprotonated Hantzsch ester–halogen EDA complexes in the presence of base, and autocatalytic photoredox processes involving transient streptocyanine-type dyes generated from tertiary amines under irradiation. These findings demonstrate that selective C–C bond formation at the anomeric position can be achieved without exogenous photocatalysts, while highlighting the non-innocent role of amines in visible light driven radical transformations.