Synthesis of a 'direct-linked' C-disaccharide from a pyranulose glycoside

Syntheses of five 'direct linked' C-disaccharides 8a-e were reported. The ( Et3SiH/BF3. Et2O) reduction of pyranulose glycoside 1 yielded (6S)- and (6R )-6-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)pyran-3(2H,6H)-one (2a and 2b ) in a ratio of ca. 2:1 and in 88% combined yield. The absolute stereochemi stry of each was determined from its CD spectrum. The reduction of 2a with NaBH4 in methanol afforded two allylic alcohols 6a and 6b in 14 and 73% yie ld, respectively. The reduction of 2b with NaBH4 afforded 6c and 6d in 30 a nd 56% yield, respectively. Cis hydroxylation of the double bond in compoun ds 6a-d with osmium tetroxide gave 7a-e. The stereoisomers 7a-e were separa ted and their configuration was established by H-1 NMR spectroscopy. Debenz oylation of compounds 7a-e with aqueous sodium carbonate produced deprotect ed C-disaccharides 8a-e. (C) 1999 Elsevier Science Ltd. All rights reserved .