Switchable Divergent Photocatalytic C-Glycosylation of Glycosyl Benzoates

Abstract

Metabolically robust C-glycosides are crucial in various biological and medical applications, underscoring the need for efficient synthesis methods. While radical C-glycosylation reactions are known for their reliability and functional group tolerance, challenges such as glycosyl donor stability and atom economy persist. In this study, we investigate the underexplored potential of condition-controlled divergent synthesis of C-glycosides through a switchable photocatalytic C-glycosylation strategy, involving reductive anomeric C─O bond cleavage. Utilizing simple, readily available, and bench-stable glycosyl benzoates as novel O-based glycosyl radical precursors, we successfully achieve deoxygenative glycosylation of simple alkenes and styryl boronic acids, establishing a versatile platform for C-glycoside synthesis. A critical aspect of the challenging reductive cleavage of these benzoate esters is the introduction of strong single-electron transfer (SET) reductants, combined with Brønsted acids to accelerate fragmentation following substrate reduction. Notably, CO2•−, generated via the consecutive photon-induced electron transfer process, is utilized for the first time in glycosylation reactions. By meticulously tuning the reaction conditions, including photocatalysts and formate additives, we facilitate the divergent synthesis of alkyl and alkenyl C-glycosides with good to high stereoselectivity and yields. Mechanistic studies provide insight into the reaction pathway and the underlying rationale behind this finely tuned, easily controlled photocatalytic system.