Nucleophilic displacement reactions in carbohydrates. Part XIX. The reaction of methyl 6-deoxy-3-O-methyl-4-O-methylsulphonyl-2-O-p-tolylsulphonyl-α-D-allopyranoside with sodium benzoate in hexamethylphosphoric triamide: a vicinal axial substituent effect

Abstract

When heated with sodium benzoate in hexamethylphosphoric triamide, the title compound (6) is converted into methyl 2-O-benzoyl-4,6-dideoxy-3-methoxy-α-D-threo-hex-3-enopyranoside (11). Debenzoylation and methylation of the latter compound gave methyl 4,6-dideoxy-3-methoxy-2-O-methyl-α-D-threo-hex-3-enopyranoside(13), which was identified by comparison with the L-enantiomer. The failure of the 4-methylsulphonyloxy-group of compound (6) to undergo direct displacement with benzoate ion is discussed and a mechanism is suggested to account for the formation of the unsaturated sugar benzoate (11).