Synthesis of C-glycopyranosylphloroacetophenone derivatives and their anomerization facilitated by 1,3-diaxial interactions Original Research Article

The reaction of 2,3,4-tri-O-benzyl-6-deoxy-α-d-glucopyranosyl fluoride, 2,3,4,6-tetra-O-benzyl-α-d-allopyranosyl fluoride, and 2,3,4-tri-O-benzyl-α-l-fucopyranosyl fluoride with 2,4-di-O-benzylphloroacetophenone, in the presence of boron trifluoride diethyl etherate, afforded, respectively, the corresponding 3-C-β-d-glycopyranosylphloroacetophenone derivatives exclusively in anomerically pure form. Alternatively, the reaction of 2,3,4,6-tetra-O-benzyl-α-d-gulopyranosyl fluoride with 2,4-di-O-benzylphloroacetophenone afforded both the 3-C-β-d-gulopyranosylphloroacetophenone derivative (4C1 conformation) as the major product and the 3-C-α-d-gulopyranosylphloroacetophenone derivative (1C4 conformation) as the minor product under identical conditions. Including the previously prepared C-glycosylphloroacetophenone derivatives that contain 3-C-β-d-glucosyl, 3-C-β-d-xylosyl, 3-C-β-2-deoxy-d-arabino-hexosyl, 3-C-β-d-galactosyl, 3-C-β-l-arabinosyl, and 3-C-α-l-arabinosyl moieties, the conformation is dictated primarily by the preference of the bulky aromatic aglycon to orient equatorially, due to the strong repulsion of the aglycon. The anomerization is directed secondarily by the presence of 1,3-diaxial interactions in the sugar moiety.