Synthesis of Methyl 2,3,6-Trideoxy-4-C-(2,5-dimethoxybenzyl)-α-l-threo-hex-2-enopyranoside

Thermal/hyperbaric heterocycloaddition of 1,4-dialkoxy-1,3-dienes: the de novo (E,Z) way to sugars

1-(Z)-Alkoxy-4-(E)-methoxybutadiene derivatives have been reacted with ethylgyoxylate and diethyl ketomalonate under thermal or hyperbaric conditions. They provide, with a total regioselectivity and fair to total endoselectivities, the expected dihydropyranic cycloadducts. Three of those pseudo-glycals have been converted in a few classical steps (deprotection, reduction, and dihydroxylation) into (racemic) allose, mannose, and gullose derivatives. The order of these three steps has a direct influence on the efficiency of the transformation and determines the stereochemistry of the final sugar.