Direct Synthesis of Unprotected C-Glycosides via Photoredox Activation of Glycosyl Ester

Abstract

Synthetic C-glycosides play a crucial role in molecular biology and medicine. With the surge of interest in C-glycosides and the demand to provide efforts with sufficient feedstock, it is highly significant to pursue novel methodologies to access C-glycosides in a concise and efficient manner. Here, we disclose an attractive strategy that diverges itself from conventional multistep reaction sequences involving the manipulations of protecting groups. Widely available native sugars first react with 1,4-dihydropyridine acids via a site-selective Mitsunobu reaction, converting them into bench-stable radical precursors. Under visible-light-enabled photoredox catalysis conditions, the resulting glycosyl radicals undergo C-C bond formation reactions, yielding a variety of C-glycosides with excellent stereoselectivity. Our method demonstrates good tolerance to a wide range of functional groups and has been successfully applied in the post-transformation of drug molecules and the preparation of C-glycosyl amino acids.