Stereoselective total synthesis of methyl alpha-D and alpha-L-glucopyranosides.

Methyl alpha-L- and alpha-D-glucopyranosides have been synthesized from methyl (R)- and (S)-(2-furyl)glycolates (3), respectively. The key intermediates, methyl 6-O-benzyl-2,3-dideoxy-L(and D)-hex-2-enopyranosid-4-uloses (13), were obtained in seven steps from the ester 3, without change of configuration of the asymmetric center, which became C-5 in the sugar molecule. Reduction of the ketone group at C-4 in the glycoside 13 with sodium borohydride afforded the corresponding methyl 6-O-benzyl-2,3-dideoxy-erythro-hex-2-enopyranosides (14). Epoxidation of the double bond in 14, followed by oxirane ring-opening in the anhydro sugar 16, and subsequent catalytic hydrogenolysis of the benzyl group led to the title compounds.