Novel 1-adamantanylthio sialosides were synthesized andcoupled to acceptors under NIS/TfOH promotion conditions.These donors showed higher reactivity than the phenylthiosialosides and could be activated by NIS/TfOH in nitrilesolvents at −78 °C to afford improved α-sialylations. Withthe N-acetyl-5-N,4-O-oxazolidinone-protected 1-adamantanylthio sialyl donor high α-selectivities could be achievedin the sialylations of both primary and sterically hinderedsecondary acceptors, including the important galactose 3-OHacceptors.