REACTIONS OF 2-ACETOXY-4,6-DI-O-ACETYL-3-O-(2,6-DICHLOROBENZOYL)-<scp>D</scp>-GLUCAL, TRI-O-ACETYL-3-DEOXY-α-<scp>D</scp>-erythro-HEX-2-ENOPYRANOSYL CHLORIDE, AND RELATED COMPOUNDS

Abstract

Attempts to dehydrobrominate tri-O-acetyl-3-O-tosyl-α-D-glucopyranosyl bromide with diethylamine led directly to products resulting from the replacement of the tosyloxy group by the diethylamine. It was readily possible to prepare 2-acetoxy-di-O-acetyl-3-(2,6-dichlorobenzoyl)-D-glucal (V). Acetolysis of this compound gave an equimolar mixture of the α- and β-anomers (II and VI, respectively) of 2-acetoxy-di-O-acetyl-pseudo-D-glucal as the first products of the reaction. Compound V reacted only reluctantly with methanol in pyridine to give a mixture of the anomeric methyl di-O-acetyl-3-deoxy-D-erythro-hex-2-enopyranosides. These glycosides were readily prepared by reaction of tri-O-acetyl-3-deoxy-α-D-erythro-hex-2-eno-pyranosyl chloride with methanol in the presence of pyridine. 2-Acetoxy-di-O-acetyl-3-O-mesitoyl-D-glucal was prepared from 3-O-mesitoyl-β-D-glucose. The anomerizations of compounds II and VI were examined with both sulfuric acid in 1:1 acetic acid – acetic anhydride and potassium acetate in acetic acid. The conformations of II and VI are discussed, as are a number of the mechanistic features of the reactions studied.