Mechanistically, the authors suggested the generation of photoactive electron-donor-acceptor complexes between the redox-active electrophile (NHPI ester or pyridinium salt), Hantzsch ester, and LiI (or Et3N) are central to the success of the developed approaches, which was supported by spectroscopy experiments. A detailed mechanism was proposed, as described in Scheme 31. The photoinduced single-electron transfer enables the generated EDA complex to undergo decarboxylative or deaminative fragmentation, affording alkyl radical species 222 . In a concurrent nickel-catalyzed cycle, a Ni(0)-mediated halogen atom abstraction enabled the formation of glycosyl radical from a glycosyl halide 215 . The resulting glycosyl radical diastereoselectively re-associates with the nickel center to produce a glycosyl-Ni(II) intermediate 228 , followed by trapping of alkyl radical 222 generated from EDA, furnishing a glycosyl-Ni(III)-alkyl species 229 . Subsequent reductive elimination of this crucial intermediate produces the desired alkyl C-glycoside adduct 218 . The active nickel catalyst 226is regenerated by a single-electron reduction of 227 .
Scheme 31 Plausible mechanism