Reductions of Methyl 2, 3-DI-O-Benzyl-4-Deoxyβ-L-Threo-Hex-4-Enodialdopyranoside

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Abstract
Selective reductions of the aldehyde and alkene functionalities in methyl 2, 3-di-O-benzyl-4-deoxy-β-L-threo-hex-4-enodialdopyranoside (4) are described. The title compound was synthesized in six steps from methyl α-D-glucopyranoside. Catalytic reduction of the C-4 - C-5 double bond in 4 gave either methyl 2, 3-di-O-benzyl-4-deoxy-α-D-xylo-hexodialdopyranoside (5) or methyl 2, 3-di-O-benzyl-4-deoxy-β-L-arabino-hexodialdopyranoside (10) in high stereoselectivity depending on the reaction conditions. The α-D-xylo product is a suitable precursor to higher-carbon sugars extended at the C-6 position. Reduction of both products with sodium borohydride gave the corresponding saturated alcohols 12 and 13. The aldehyde group in the title compound was reduced with diisobutylaluminum hydride to give allylic alcohol 11 which was hydrogenated to give, unexpectedly, alcohol 12 as the only product.