Abstract Unprotected methyl D-glycosides were selectively acylated by using thiazolidine-2- thione and 2-mercapto-5-methyl-1, 3, 4-thiadiazole alkoxycarbonyl or carbonyl derivatives. Under suitable conditions the corresponding 6-O-alkoxycarbonyl compounds or the cyclic Five or six membered carbonates could be obtained.