NUCLEOPHILIC DISPLACEMENT REACTIONS IN CARBOHYDRATES .12. REACTION OF 6-DEOXY-2,3-O-ISOPROPYLIDENE-4-O-METHANESULPHONYL-ALPHA-L-TALOPYRANOSE WITH SODIUM METHOXIDE

Oxidation of benzyl 6-deoxy-2,3-O-isopropylidene-α-l-mannopyranoside (3) with ruthenium tetroxide in carbon tetrachloride gave benzyl 6-deoxy-2,3,-O-isopropylidene-α-l-lyxo-hexopyranosid-4-ulose (4) in excellent yield. Ketone 4 was reduced stereospecifically, with sodium borohydride in methanol, to yield benzyl 6-deoxy-2,3-O-isopropylidene-α-l-talopyranoside (5), which was converted into the crystalline 4-methanesulphonate 6. Catalytic debenzylation of methanesulphonate 6 gave 6-deoxy-2,3-O-isopropylidene-4-O-methanesulphonyl-α-l-talopyranose (7), which, on solvolysis with sodium methoxide in methanol at room temperature, was converted into 1,4-anhydro-6-deoxy-2,3-O-isopropylidene-α-l-mannopyranose (1,5-anhydro-6-deoxy-2,3-O-isopropylidene-β-l-mannofuranose) (9, 58%), methyl 6-deoxy-2,3-O-isopropylidene-α-l-talofuranoside (12, 26%), and methyl 6-deoxy-2,3-O-isopropylidene-α-l-mannofuranoside (14, 12%). The mechanisms of formation of these products are discussed. © 1969.