Thioester-assisted α-sialylation reaction

α-Selective sialylation reactions were carried out using novel sialic acid building blocks that possess a thioester auxiliary. In contrast to other arylthio- and benzylthioester derivatives, sialyl phosphite 1a (with the phenylthioester moiety) was employed as the α-selective building block, and was reacted with various primary alcohols, including the C6–OH group of galactose and glucose, with moderate to excellent α-selectivities. For C3–OH of the galactose, 4,6-di-O-benzylgalactal afforded desired α-linkage with excellent selectivity.