N- and C-Glycosylation of 6,7-Difluoro-1,4-dihydro-4-oxo-3-quinoline Carboxylic Acid Ethyl Ester

1,2,3,4,6-Penta-O-acetyl-α-D-glucopyranose reacts with a silylated ethyl ester of 6,7-difluoro-1,4-dihydro-4-oxo-3-quinoline carboxylic acid 1 with C-glycosylation to subsequently afford the ethyl ester of 8-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)- 6,7-difluoro-1,4-dihydro-4-oxo-3-quinoline carboxylic acid 4; on the contrary, condensation of 1,2-di-O-acetyl-3,5-di-O-benzoyl- D-xylofuranose with the heterocycle 1 results in an N-glycosylation product 2.