Koenigs–Knorr Syntheses of some α-1 → 2 and β-1 → 2 linked Nitro Disaccharides

2,3,4,6-Tetra-O-benzyl-α-D-glucopyranosyl bromide (1) and, in one instance, its α-D-galacto isomer (2) were condensed under conditions of the Heiferich modification of the Koenigs–Knorr reaction with the four stereoisomeric methyl 4,6-O-benzylidene-3-deoxy-3-nitrohexopyranosides having the α-D-galacto (3), β-D-galacto (4), α-D-gluco (5), and β-D-gluco (6) configurations. Six new, 1 → 2 linked, fully blocked nitro disaccharides (7–12) were isolated. The configurations of the disaccharidic linkages were established by n.m.r. spectroscopy to be α in four of the products (8, 9, 11, and 12) and β in two (7 and 10). The steric course of the disaccharide bond formation was found to depend on the anomeric as well as the over-all configuration of the alcoholic components 3–6.