Stereoselective synthesis and structure elucidation of spiro-ketodisaccharides

Abstract Cycloglycosylation of 3,4,5,7-tetra- O -benzyl-α- d -hept-2-ulopyranoses ( 2a – c ) was carried out stereoselectively under the catalysis of Lewis acid to afford two spiro-cyclodisaccharides 3a – c and 4a – c in good yields. The reaction provided the kinetic products 3a – c or the thermodynamic products 4a – c as the predominant products under different conditions, respectively. The unprotected disaccharides 5a – c and 6a – c and the acetylated derivatives 7a – c and 8a – c were prepared by catalytic hydrogenation and followed by acetylation. The structures of compounds 4a – c , 6a – c and 8a – c were confirmed to be α,β-anomeric configuration with chair–chair–chair form for the tri-cycles based on the X-ray crystallographic analysis of 6a – c . The α,α-anomeric configurations of compounds 3a – c , 5a – c and 7a – c were determined based on the measurements of the three bond coupling constants 3 J C,H between the C-1 and the H-3 of 7a – c .