Unsaturated carbohydrates. Part V. Displacements of 4- and 6- sulphonyloxy-groups from methyl 2,3-didehydro-2,3-dideoxyhexopyranoside derivatives
Methyl 2,3-didehydro-2,3-dideoxy-4,6-di-O-methanesulphonyl-α-D-erythro- and -threo-hexoside, on treatment with sodium benzoate in dimethylformamide solution, undergo direct displacement of the 4-sulphonyloxy-group with inversion of configuration followed by reaction at the primary site. In experiments designed to give mixed products, methyl 4-O-benzoyl-2,3-didehydro-2,3-dideoxy-6-O-methanesulphonyl-α-D-threo-hexoside and methyl 4,6-di-O-benzoyl-2,3-didehydro-2,3-dideoxy-α-D-threo-hexoside were obtained from the erythro-disulphonate in a combined yield of 64%; the corresponding erythro-products were isolated in 67% yield. No evidence was obtained for the formation of compounds having a 3,4-double bond.