Synthesis of 1-C-alkyl-α-D-glucopyranosides by Lewis acid- or Bronsted acid-catalyzed O-glycosidation

We prepared several kinds of 1-C-alkyl-2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranose derivatives containing methyl, ethyl, n-butyl, and benzyl groups as the alkyl groups at their anomeric positions. The Lewis acid- or Br phi nsted acid-catalyzed O-glycosidations using them as the glycosyl donors to synthesize 1-C-alkyl-D-glucopyranosides were investigated. Using 10 mol % of triphenylmethyl perchlorate efficiently catalyzed the glycosidation of 2,3,4,6-tetra-O-benzyl-1-C-methyl-alpha-D-glucopyranosyl dimethylphosphinothioate. The glycosidation using the 1-C-alkyl-2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl acetates smoothly proceeded in the presence of only 5 mol % of scandium(III) trifluoromethanesulfonate. The dehydration-condensation type glycosidation using the 1-C-alkyl-2,3,4,6-tetra-O-benzyl-alpha-D-glueopyranoses was significantly promoted using 5 mol % of bis(trifluoromethane)sulfonimide. These glycosidations successfully afforded various 1-C-alkyl-alpha-D-glucopyranosides in good yields with high alpha-stereoselectivities. (c) 2006 Published by Elsevier Ltd.