Based on experimental mechanistic studies and the 1,2-RaM reactivity, 17 a proposed catalytic cycle is outlined in Scheme 5E. Photoexcitation of [Pd 0 ] generates the excited [Pd 0 ]* species that reacts with α-bromosugar 1 through an inner-sphere single electron transfer (SET), To elucidate the origins of axial/equatorial and terminal/internal alkene selectivities, we performed computational studies to investigate the reaction pathways leading to the allylation product from the photochemically generated C2-radical intermediate IIIa (Scheme 6). DFT calculations revealed that the free energy barrier for the addition of α-methylstyrene 2 to the axial position of IIIa (TS1) was 1.8 kcal/mol lower than that to the equatorial addition (TS2). Here, the axial addition leading to the 1,2-trans product is sterically favored, as a steric repulsion between Ph on the alkene and the axial C1-OAc destabilizes the equatorial addition transition state TS2. Subsequent β-H elimination from the benzyl Pd(II) intermediate IVb favors hydride elimination from the less substituted carbon (TS3) leading to the external alkene product 3-ext over elimination from the more substituted carbon (TS4) leading to the internal alkene product 3-int. This kinetic selectivity is attributed to the steric repulsion in TS4 in which the pyranose ring is placed adjacent to a more hindered region of the XantPhos ligand occupied by two pseudoaxial P-Ph groups. By contrast, in TS3, a much less hindered primary carbon is placed towards these pseudoaxial P-Ph groups, leading to diminished ligand-substrate steric repulsions. DFT calculations indicate that the alternative reaction pathways, such as Pd(I)-catalyzed H-atom abstraction, Br-atom transfer, and oxidation of intermediate IVa are unlikely (Figure and Figure ).