To gain better insight into the key regio-and stereodetermining steps of the reaction, the relevant mechanistic steps were investigated through density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) level of theory using the Grimme correction for dispersion (D3) and the Conductor-like Polarizable Continuum Model (CPCM, UFF, MeCN), as implemented in the Gaussian 16 software (see the Supplementary Information for details). The calculations were performed with α-and β-configured model glycoside substrates derived from D-glucose (2a and 2c) and D-galactose (2b and 2d) (Fig. ). The experimentally observed 1,6-HAT pathway was found to be consistently favorable for all of the substrates, while the alternative 1,5-HAT pathway was less favorable both kinetically and thermodynamically. The formation of the C4-centered endocyclic radicals (2-C4-rad) upon the regioselectivity-determining 1,6-HAT step proceeds with reasonably low barriers (ΔG ‡ = 11.6-13.6 kcal mol -1 ) and a substantial driving force (ΔG = -6.1 to -7.5 kcal mol -1 ). Depending on the C4-configuration of the initial sugar, the latter step produces either axial (2a/c-C4-rad-ax) or equatorial (2b/d-C4-rad-eq) C4-radical intermediates displaying pyramidal geometry. Subsequently, these intermediates engage in a rapid axial/equatorial interconversion (ΔG ‡ = 2.6-4.8 kcal mol -1 ) with only minimal energy differences between the stable conformers (ΔG = 0.9 kcal mol -1 ) for both α-and β-configured substrates. The following C-C bond forming reaction between the C4-radical and the acrylate somophile exhibits significantly higher reaction barriers (ΔG ‡ = 7.2-10.1 kcal mol -1 ) and considerable driving forces (ΔG = -6.6 to -8.9 kcal mol -1 ), identifying this as the stereoselectivity determining step for the overall transformation. The latter implies that the stereochemical outcome of the reaction can be estimated using the Curtin-Hammet principle, according to which the ratio of products is defined only by the difference in energy of the barriers leading to the alternative products (ΔΔG ‡ = 2.0 and 0.6 kcal mol -1 for α-and β-glycosides, respectively) and not by the difference in energy between the unstable intermediates. Thereby, the predicted ratios of gluco/galacto products amount to 1:30 for α-configured substrates and to 1:3 for β-configured substrates.