Article Autocondensation Glycosylation reactions Hydroxyl groups Innovative approaches Oligosaccharides Regio-selective Regioselectivity Thioglycosides acetylation acylation alkylation benzylation carbohydrate synthesis conformation conformational transition deacylation disaccharide furan derivative galactose oligosaccharide glycosylation hydroxyl group ion transport n acetylgalactosamine oligosaccharide one pot synthesis regioselectivity ring opening stereochemistry thioglycoside