Synthesis of 2-(α-d-glucopyranosyl)benzoic acid by an intramolecular Friedel—Crafts reaction

6-O-Acetyl-2,3,4-tri-O-benzyl-α-d-glucopyranosyl chloride reacted with silver tetrafluoroborate to give the internal C-glycoside, 1,2″-anhydro-2′-(6″-O-acetyl-3″,4″-di-O-benzyl-α-d-glucopyranosyl)phenylmethanol (2) with complete α-stereoselectivity and good yield. Oxidation of 2 by ruthenium (VIII) oxide gave the lactone, 3,4-dihydro-(6-O-acetyl-3,4-di-O-benzoyl-1,2-dideoxy-α-d-glucopyranoso)[2,1-c]-2-benzopyran-1-one the structure of which was analysed by X-ray diffraction. Alternatively, treatment of 2 by ozone followed by methanolysis gave the title product in 60% yield.