GLYCOSYLIDENE CARBENES .10. REGIOSELECTIVE GLYCOSIDATION OF 4,6-O-BENZYLIDENE-D-ALTROPYRANOSIDES

Glycosidation by the diazirine 1, the trichloroacetimidate 4, and the bromide 5 of the altro-diol 2, possessing an intramolecular H-bond (HO-C(3) to O-C(l)) in solution, but not in the solid state, proceeds with high and complementary regioselectivity. From 2 and 1, one obtains mostly the 1,2-linked disaccharides 10 and 11 (beta-D > alpha-D), together with the 1,3-linked isomers 12 and 13 (alpha-D > beta-D; 1,2-/1,3-linked products ca. 9: 1), the demethylated 1,3-linked disaccharides 24-27, the trisaccharides 19-22, the lactone azines 23, and the hydroxyglucal 18, while 2 reacted with 4 or 5 to yield mostly the 1,3-linked disaccharides (1,2-/1,3-linked products ca. 1:9). The disaccharides were additionally characterized as acetates (-->14-17, 28-31). Yields and stereoselectivity depended upon the donor, stoichiometry, solvent, temperature, and concentration. Glycosidation of the 1,3-linked disaccharides with 1 yielded the trisaccharides 19-22. Reaction of the beta-D-altro- diol 3 with 1 gave the 1,2- and 1,3-linked disaccharides 32/33 and 34/35 in a 1:1 ratio, characterized as the acetates 36-39, while glycosidation with 5 according to Lemieux proceeded regioselectively (1,2-/1,3-linked products 91:9). The monotosylates 6 and 7 reacted with 1 to yield the anomeric pairs 40/41, and 42/43 of the tosylated disaccharides; the oxiranes 44 and 45 were not observed.