O-Glycosidation of totally O-unprotected D-galacturonic acid 1 in THF provides α-pyranosides 4a when promoted with BF3·OEt2 whereas β-furanosides 6β were obtained in the presence of FeCl3; when the same reaction is performed with D-glucuronic acid 2 or ‘D-glucurone’3, alkyl-D-glucofuranosidurono-6,3-lactones 7 are synthesized in excellent yields and high β-selectivity.