SYNTHESIS AND SOLVOLYSIS OF SOME D-GLUCOPYRANOSYL BROMIDES HAVING A BENZYL GROUP AT C-2

The long-range effect of p-nitrobenzoyl vs. benzyl groups on the formation and solvolysis of various dglucopyranosyl bromides, all having a benzyl group at C-2, has been studied. For this purpose, 2-O-benzyl-3,4,6-tri-O-p-nitrobenzoyl-α-D-glucopyranosyl bromide (α 3), its anomer (β 3), 2,3-di-O-benzyl-4,6-di-O-pnitrobenzoyl-β-D-glucopyranosyl bromide (β 7), 2,3,4-tri-O-benzyl-6-O-p-nitrobenzoyl-β-D-glucopyranosyl bromide (β 9), and 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl bromide (α 11) have been synthesized through the action of hydrogen bromide on the corresponding 1-O-p-nitrobenzoyl esters in dichloromethane solution. In each case, and regardless of the anomeric configuration of the esters used, the β-D-glucopyranosyl bromide is formed first; equilibration with the more stable β-D-glucopyranosyl bromide then follows at a rate which is inversely related to the number of p-nitrobenzoyl groups present in the halide. The rates of methanolysis of the five n-glucopyranosyl bromides, with and without added bromide ion, have been measured and the ratio of methyl D-glucopyranosides has been determined in each case. In general, the β-D-glucopyranosyl bromides are more reactive than their α anomers and, with one exception, the α-D-glucopyranoside is the main product regardless of the anomeric configuration of the halide used. These and other facts suggest that the more rapid solvolysis of the equatorial bromides is probably the dominant feature of these reactions. Theoretical considerations aside, β 3 has been found to be an easily accessible substance and may prove valuable in the synthesis of α-D-glucopyranosides. © 1969, American Chemical Society. All rights reserved.