Stereoselective syntheses of C-(D-glucopyranosyl)alkenes

alpha-D-Glucopyranose pentaacetate (1) was found to undergo stereoselective conversion in good yield into 3-(tetra-O-acetyl-alpha-D-glucopyranosyl)-1-propene (4) by treatment with allyltrimethylsilane and boron trifluoride etherate in acetonitrile. Similar treatment of methyl tetra-O-acetyl-alpha-D-glucopyranoside or tetra-O-acetyl-alpha-D-glucopyranosyl bromide also gave 4 in preference to its beta anomer, but net yields were lower. Similar reaction of 1 with (E)-penta-2,4-dienyltrimethylsilane afforded the readily polymerizable 5-(tetra-O-acetyl-alpha-D-glucopyranosyl)-(E)-1,3-pentadiene, accompanied by a minor proportion of its beta anomer.