Abstract
Benzylidenation of 1, 6-anhydro-β-lactose afforded 1, 6-anhydro-4', 6'-O-benzylidene-β-lactose (2) in 81% yield. Acylation of 2 yielded tetra-O-acyl-1, 6-anhydro-4', 6'-O-benzylidene-β-lactose [acyl=acetyl (3), benzoyl (4)]. Reflux of 3 with N-bromosuccinimide and BaCO3 in CCl4 and 1, 2-dichloroethane gave crystalline tetra-O-acetyl-1, 6-anhydro-4'-O-benzoyl-6'-bromo-6'-deoxy-β-lactose (5) in 52% yield. Catalytic dehydrobromination of 5 afforded crystalline tetra-O-acetyl-1, 6-anhydro-4'-O-benzoyl-6'-deoxy-β-lactose (6). Deacylation of 5 and successive reacetylation yielded 2, 2', 3, 3', 4'-penta-O-acetyl-1, 6-anhydro-6'-bromo-6'-deoxy-β-lactose (7). Dehydrobromination of 7 gave penta-O-acetyl-1, 6-anhydro-6'-deoxy-β-lactose (8). Heating of 7 and sodium azide in hexamethylphosphoric triamide afforded a mixture of crystalline penta-O-acetyl-1, 6-anhydro-6'-azido-6'-deoxy-β-lactose (9) (36%) and sirupy 2, 3-di-O-acetyl-1, 6-anhydro-4-O-(2, 3, 4-tri-O-acetyl-α-L-arabino-hex-5-eno-pyranosyl)-β-D-glucopyranose (10) (34%). Compound 10 was also prepared by treatment of 7 in dry pyridine with silver fluoride. Acetolysis of 9, reduction of the azido group in the acetolysis product (11), N-acetylation, and finally de-O-acetylation afforded the title compound (13) as hydroscopic crystals, [α]24D+80°→+66.7°. In catalytic hydrogenation of 10 over Pd catalyst, 8 was the sole product in 90% yield. Over Pt oxide or Raney Ni catalyst, a low yield of 8 was effected with fairly amounts of unidentified sirup.
