Synthesis of C-pentopyranosylphloroacetophenone derivatives and their anomerization

A 3-C-β-d-xylopyranosylphloroacetophenone derivative was synthesized via reaction of 2,3,4-tri-O-benzyl-α-d-xylopyranosyl fluoride and 2,4-di-O-benzylphloroacetophenone in the presence of boron trifluoride diethyl etherate. Alternatively, the reaction of 2,3,4-tri-O-benzyl-β-l-arabinopyranosyl fluoride with 2,4-di-O-benzylphloroacetophenone afforded both the 3-C-α-l- and the 3-C-β-l-arabinopyranosylphloroacetophenone derivatives under identical reaction conditions. The C-β-l-arabinoside, the thermodynanic product, was produced via anomerization of the C-α-l-arabinoside, the kinetic product during the reaction. The composition of this product mixture is apparently dictated by both 1,3-diaxial and 2,4-diaxial interactions.