Convenient preparation of l-arabino-hexos-5-ulose derivatives from lactose Original Research Article

2,6-Di-O-benzyl- (9), 2-O-benzyl-3,4-O-isopropylidene- (19), and 2-O-benzyl-6-O-m-chlorobenzoyl-l-arabino-hexos-5-ulose (20) have been prepared using 4′-deoxy-4′-eno- and 6′-deoxy-5′-eno lactose dimethyl acetal derivatives 7 and 14 as key intermediates. The synthesis of enol ethers 7 and 14 has been performed with good yields by base-promoted elimination of acetone or p-toluenesulfonic acid from 2′,6′-di-O-benzyl-, and 6′-O-p-toluenesulfonyl-2,3:5,6:3′,4′-tri-O-isopropylidenelactose dimethyl acetal, respectively. The epoxidation with MCPBA of 7 and 14 in methanol or dichloromethane furnishes C-5′-methoxy and C-5′-m-chlorobenzoyloxy derivatives, easily transformed with good yields into l-arabino 5-ketoaldohexoses 9, 19 and 20.