Syntheses of N-acetyl- d-neuraminic acid derivatives are reported. Methyl 4,7,8,9-tetra- O-acetyl- N-acetyl-2-chloro-2-deoxy-β- d-neuraminate ( 3) was prepared directly from methyl N-acetyl-β- d-neuraminate ( 2) in good yield. Koenigs-Knorr reaction of 3 with an excess of methanol gave the methyl α-glycoside of methyl N-acetyl- d-neuraminate ( 4). 2,3- O-Isopropylidene- d-ribono-1,4-lactone, 2,3- O-isopropylideneuridine, and 5-fluoro-2,3- O-isopropylideneuridine reacted with 3 to give anomeric mixtures of methyl N-acteyl- d-neuraminate derivatives. The stereochemistry of these compounds was confirmed from n.m.r. and c.d. spectra, and measurements of the rate of hydrolysis of the glycosidic bond.