Selectivity in the SmI2-induced deoxygenation of thiazolylketoses for formyl C-glycoside synthesis and revised structure of C-ribofuranosides

Deoxygenation of thiazolylketose acetates using SmI2–(CH2OH)2 or TMSOTf–Et3SiH affords thiazolyl C-glycosides with opposite α/β ratios. Examination of the thiazolyl α- and β-C-ribofuranoside pair by NOE experiments reveals that the earlier configuration assigned to one of these isomers has to be revised. Having prepared authentic anomeric α- and β-ribofuranose aldehydes from the corresponding thiazolyl C-glycosides by cleavage of the thiazole ring, each aldehyde was transformed into (1→6)-C-disaccharides via Wittig olefination with a galactose 6-phosphorane.