Email Record: X-Ray crystallographic and n.m.r. (^1H and ^1^3C) studies of methyl 4,6-O-(R)-benzylidene-3-O-methyl-2-O-p-tolylsulfonyl-α-d-glucopyranoside and methyl 4,6-O-(R)-benzylidene-2-O-methyl-3-O-p-tolylsulfonyl-β-d-glucopyranoside