Sialylation reactions: Expanding the C-5 effect to phosphate leaving groups.

With the expanding use of phosphates as leaving groups in sialylations, little remains known about the C-5 effect towards their reactivity and stereoselectivity in the presence of a range of acceptors, and in different solvents. Herein we report the comparison between sialyl phosphate donors bearing N-acetyloxazolidinone and trifluoroacetamido functionalities at C-5. Excellent results and complete stereoselectivity were observed in several sialylations, but the outcome was influenced by the nature of the solvent and/or glycosyl acceptor.