α-Selective Sialylations at −78 °C in Nitrile Solvents with a 1-Adamantanyl Thiosialoside

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Abstract
Novel 1-adamantanylthio sialosides were synthesized and coupled to acceptors under NIS/TfOH promotion conditions. These donors showed higher reactivity than the phenylthio sialosides and could be activated by NIS/TfOH in nitrile solvents at −78 °C to afford improved α-sialylations. With the N-acetyl-5-N,4-O-oxazolidinone-protected 1-adamantanylthio sialyl donor high α-selectivities could be achieved in the sialylations of both primary and sterically hindered secondary acceptors, including the important galactose 3-OH acceptors.