Synthesis of CH2-linked α(2,3)sialylgalactose analogue: On the stereoselectivity of the key Ireland-Claisen rearrangement

A CH2-linked α(2,3)sialylgalactose analogue was efficiently synthesized using an Ireland-Claisen rearrangement, which was developed recently by our group for constructing a CF2-sialoside. The reaction conditions of the rearrangement were optimized for α-stereoselective formation of the CH2-sialoside. On the basis of the observed temperature effects, the origin of the stereoselectivity of the Ireland-Claisen rearrangement is discussed. Moreover, reconstruction of the 2α-hydroxyl group on the galactose unit of the rearrangement product was achieved by means of stereoselective dihydroxylation and deoxygenation.