On the Origin of Regioselectivity in Palladium-Catalyzed Oxidation of Glucosides

The palladium-catalyzed oxidation of glucopyranosides has been investigated using relativistic density functional theory (DFT) at ZORA-BLYP-D3(BJ)/TZ2P. The complete Gibbs free energy profiles for the oxidation of secondary hydroxy groups at C2, C3, and C4 were computed for methyl beta-glucoside and methyl carba-beta-glucoside. Both computations and oxidation experiments on carba-glucosides demonstrate the crucial role of the ring oxygen in the C3 regioselectivity observed during the oxidation of glucosides. Analysis of the model systems for oxidized methyl beta-glucoside shows that the C3 oxidation product is intrinsically favored in the presence of the ring oxygen. Subsequent energy decomposition analysis (EDA) and Hirschfeld charge analysis reveal the role of the ring oxygen: it positively polarizes C1/C5 by inductive effects and disfavors any subsequent buildup of positive charge at neighboring carbon atoms, rendering C3 the most favored site for the beta-hydride elimination.

Automated summary

The palladium-catalyzed oxidation of glucopyranosides was investigated using relativistic density functional theory, showing the crucial role of the ring oxygen in the oxidation process and the importance of C3 regioselectivity.