Based on literature precedents and a previous radical trapping experiment, [15] the authors proposed a mechanism shown in Scheme 26-B. The key step involves the subsequent fragmentation of the DHP ester to deliver glycosyl radicals upon the release of Hantzsch pyridine and dioxide. Another important step is the activation of the carboxylic acid by DEDC (diethyl decarbonate). The oxidative addition of the resulting mixed decarbonates 192 by Ni(0) species 191 delivers Ni(II) intermediate 193 , followed by capturing glycosyl radical 189 to form acyl-Ni(III)-glycosyl complex 194 . Subsequently, the reductive elimination of194 produces the desired acyl C-glycosides 183 and Ni(I)Br 190 . Ni(I)Br is reduced by reduced photocatalyst to regenerate active Ni(0) catalyst 191 .
Scheme 26 Synthetic application and plausible mechanism