Regioselective synthesis of 4azido-Neu2en5,7Ac21Me and its intramolecular transformation to 4azido-Neu2en5,9Ac21Me

Methyl 5-N-acetyl-7-O-acetyl-4-azido-2,3-didehydro-2,4-dideoxy-neuraminic acid (4azido-Neu2en5,7 Ac21Me) was synthesized regioselectively starting from 4azido-Neu2en5Ac1Me in high yield. The transformation of 4azido-Neu2en5,7Ac21Me to the corresponding thermodynamically stable 4azido-Neu2en5,9Ac21Me via intramolecular acetyl migration was confirmed by single-crystal X-ray diffraction analysis. The proposed rearrangement mechanism is discussed.