O-Glycosylation of a variety of long chain alcohols with totally unprotected uronic acids (D-glucuronic and D-galacturonic acids) and neutral carbohydrates (D-glucose, D-galactose, D-mannose and D-glucofuranurono-6,3-lactone), performed in heterogeneous media and promoted by Lewis acids (ferric chloride or boron trifluoride diethyl etherate), afforded alkyl D-glycofuranosiduronic acids and alkyl D-glycofuranosides, respectively, in high yields. Both chemoselectivity and anomeric stereoselectivity were enhanced by complexing agents, i.e. calcium or barium chloride. (C) 1998 Elsevier Science Ltd. All rights reserved