PREPARATION OF SOME 2-DEOXY-GLYCOSYL FLUORIDES AND 2,6-DIDEOXY-GLYCOSYL FLUORIDES

Treatment of 1,3,4,6-tetra-O-acetyl-2-deoxy-D-arabino-hexose (1) and 1,3,4-tri-O-acetyl-2,6-dibromo-2,6-dideoxy-D-glucose (7) with HF.pyridine gave the corresponding alpha-glycosyl fluorides 2 and 9, respectively, wheras treatment of 3,4,6-tri-O-acetyl-2-deoxy-D-arabino-hexose (4) and of 3,4-di-O-acetyl-2,6-dibromo-2,6-dideoxy-D-glucose (8) with diethylaminosulfur trifluoride (DAST) led to mixtures of the alpha- and beta-fluorides 2 and 5, and 9 and 12, respectively. The 3,4,6-tri-O-acetyl-2-bromo-2-deoxy-beta-D-glucopyranosyl fluoride (6) was obtained as the only product from treatment of 3,4,6-tri-O-acetyl-2-bromo-2-deoxy-alpha-D-glucopyranosyl bromide (3) with silver fluoride. Similarly, the 3,4-di-O-acetyl-2,6-dibromo-2,6-dideoxy-alpha-D-glucopyransoyl bromide (17) gave the corresponding beta-fluoride (12) by treatment with silver fluoride. The 3,4-di-O-acetyl-2,6-dibromo-2,6-dideoxy-D-mannopyranosyl derivatives (19, 20, 21) all gave the 3,4-di-O-acetyl-2,6-dibromo-2,6-dideoxy-alpha-D-mannopyranosyl fluoride (22) by the three methods mentioned. The bromodeoxy-glucosyl fluorides 6, 9, 12 and 22 were converted into 2-deoxy- and 2,6-dideoxy-alpha- or -beta-glycosyl fluorides (5, 11 and 16) by treatment with tributylstannane. Deacetylation of the glycosyl fluorides 9 and 22 gave the deprotected fluorides, 2,6-dibromo-2,6-dideoxy-alpha-D-gluco- (10) and -D-mannopyranosyl fluoride (23), respectively. Benzylation of the glucosyl fluoride 10 gave the 3,4-di-O-benzylated fluoride 15, whereas the mannosyl fluoride 23 reacted to give the mono-O-benzylated 3,6-anhydro sugar 14 as the only product.