PhBCl2 promoted reductive opening of 2′,4′-O-p-methoxybenzylidene: new regioselective differentiation of position 2′ and 4′ of α-l-iduronyl moieties in disaccharide building blocks

We describe a new protocol for the challenging differentiation of the position 2′ and 4′ of l-iduronyl moieties located at the nonreducing end of various disaccharide building blocks. This methodology is based on the introduction of a 2′,4′-O-p-methoxybenzylidene group, followed by a totally regioselective reductive opening of this acetal by the PhBCl2/Et3SiH reagent system. l-Iduronyl moieties protected by a 4′-O-p-methoxybenzyl group were thus obtained regioselectively and efficiently.