Decreasing the concentration of the reaction suppressed formation of the premature addition sideproduct, while preventing the reductive dehalogenation side-reaction proved considerably more challenging. Several alternative mechanistic strategies were assessed, including the use of supersilanol, bis(catecholato)borate, formate, dimanganese decacarbonyl, as well as carboxylate, 49 phosphorous 26 or boron-based 27 co-catalysts, with no positive influence on the reaction outcome. Alternative redox-active silyl tethering groups, including (iodomethyl)diphenylsilyl and (2iodophenyl)dimethylsilyl groups, also proved ineffective. Gratifyingly, adjusting the ratio of the coupling partners and further screening of the photocatalyst, sacrificial reductant/XAT-agent, and the solvent allowed transformation of the methyl α-D-glucoside substrate 2a into the desired C4-functionalized product 3a in a reasonably high yield of 72% (Fig. , and Fig. , entry 1). The optimal conditions for further investigation of the reaction included the use of [Ir(dF(CF3)ppy)2(dtbbpy)](PF6) (PC1) as the photocatalyst under 440 nm LED irradiation, N,N-diisopropylethylamine ( i Pr2NEt) as the XAT-agent, and MeCN/ t BuOH 9:1 as the solvent mixture. Increasing the concentration of the substrates or excluding t BuOH as a co-solvent had a marginally detrimental effect (entries 2 and 3), while conducting the reaction in dark or in the absence of the photocatalyst completely impeded conversion of the substrate (entries 4 and 5). Alternative oxidizing photocatalysts with comparable redox properties to PC1 proved less effective (entries 6, 7 and 8). Notably, the organic 4CzIPN photocatalyst (PC2) delivered product 3a in a reasonably good yield of 60% (entry 6), exemplifying an attractive variation of the disclosed protocol that does not require any metal-containing reaction components.