Thermal/Hyperbaric Heterocycloaddition of 1,4-Dialkoxy-1,3-dienes: The de novo (E,Z) Way to Sugars
摘要:
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 pseudoglycals 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.
Thermal/Hyperbaric Heterocycloaddition of 1,4-Dialkoxy-1,3-dienes: The de novo (E,Z) Way to Sugars
摘要:
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 pseudoglycals 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.
An unprecedented enantioselective deprotonation/conjugate elimination sequence, which transforms an allylic meso-dioxepane into a chiral diene, is described. The best desymmetrization conditions (ee up to 70%) involve s-BuLi and sparteine at -78 degrees C in THF.