NUCLEOPHILIC DISPLACEMENT REACTIONS IN CARBOHYDRATES .9. SOLVOLYSIS OF METHYL 6-0-METHANESULPHONYL-2,3-DI-0-METHYL-BETA-D-GALACTOPYRANOSIDE - A METHOXY-GROUP PARTICIPATION

The solvolysis of methyl 6-O-methanesulphonyl-2,3-di-O-methyl-β-d-galactoyranoside (8) in boiling 50% aqueous methanol, in the presence of sodium acetate afforded three products which were identified as methyl 3,6-anhydro-2-O-methyl-β-d-galactopyranoside (9), methyl 2,3,6-tri-O-methyl-β-d-galactopyranoside (12), and methyl 2,3-di-O-methyl-β-d-galactopyranoside (7). Anhydro-sugar 9 is considered to result from attack of solvent on an oxonium-ion intermediate 14, formed as a consequence of methoxy-group participation in displacement of the sulphonic ester group, while compounds 7 and 12 may result either from solvent attack upon the oxonium ion or from a solvent-assisted displacement of the sulphonic ester group. © 1969.