DAST-mediated regioselective anomeric group migration in saccharides.

When saccharides bearing a sulfur, selenium, or oxygen substituent at the anomeric center and an unprotected hydroxyl group either at C-4 or C-6 were subjected to fluorination with DAST in dichloromethane, a regioselective migration of the anomeric substituent to the C-4 or C-6 position was observed. Certain saccharides gave a mixture of migration and normal fluorination products whereas others yielded mainly or exclusively migration products (beta-glycosyl fluorides). The high thermal and chemical stability of migrated glycosyl fluorides were demonstrated to be an important precursor for many significant carbohydrate analogies. It is therefore suggested that these migrations may have useful applications in organic synthesis.