Synthesis of α-C-glycoside conjugates via a Giese-like reaction triggered by photoactivated electron donor–acceptor (EDA) complexes and in situ photocatalytic species

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 iodides 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 a 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.