Nucleophilic displacement reactions in carbohydrates. Part V. Reaction of 2,3-O-isopropylidene-5-O-methylsulphonyl-D-lyxofuranose with sodium methoxide: aldehyde-group participation

Abstract

2,3-O-Isopropylidene-5-O-methylsulphonyl-D-lyxofuranose has been prepared by an unambiguous route from 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose. Treatment of the methylsulphonate with sodium methoxide in methanol gave principally methyl 2,3-O-isopropylidene-β-L-ribofuranoside, with inversion of configuration at C-4 of the lyxose derivative. The reaction is considered to involve the initial formation of 4,5-anhydro-2,3-O-isopropylidene-aldehydo-D-lyxose, which undergoes opening of the epoxide ring at C-4 with neighbouring-group participation by the aldehyde group.