Access to tetrachlorophthalimide-protected ethyl 2-amino-2-deoxy-1-thio-β-d-glucopyranosides

Ethyl 2-deoxy-2-tetrachlorophthalimido-1-thio-β-d-glucopyranoside (7) was prepared from glucosamine hydrochloride in four steps with a 20–25% overall yield. Formation of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-tetrachlorophthalimido-β-d-glucopyranoside (5) was found to be crucial for this reaction sequence since the corresponding α-1-acetate did not react in Lewis-acid-catalyzed ethylthio glycosidations. Formation of the β-1-acetate (5) was achieved by treatment of 3,4,6-tri-O-acetyl-2-deoxy-2-tetrachlorophthalimido-α-d-glucopyranosyl bromide (4) with acetic acid under silver zeolite promotion. This was necessary because conditions normally used for β-1-acetate formation were not tolerated by the tetrachlorophthalimido (TCP) group.