Utilisation d'ylides du phosphore en chimie des sucres : IX. Élaboration de ramifications des types a et b sur le carbone 4 d'un pyranoside

Abstract

cis-Dihydroxylation with potassium permanganate of a mixture of cis and trans isomers of methyl 4- C-cyanomethylene-4-deoxy-2,3- O-isopropylidene-6- O-methyl-α- D- lyxo-hexopyranoside is stereospecific and leads to a branched sugar having a gem-hydroxyl-formyl group and to which the α- D- manno configuration was attributed on the basis of the easier access to the side of the double bond located in trans with respect to the dioxolane ring. When treated with Raney nickel, cis and trans methyl 4-deoxy-2,3- O-isopropylidene-6- O-methyl-4- C-methylthiomethylene-α- D- lyxo-hexopyranosides gave a mixture of branched 4-deoxy-4-methyl sugars with the α- D- manno and α- D- talo configurations, whereas their C-5 epimers having the β- L- ribo configuration gave branched sugars with the β- L- gulo and β- L- allo configurations. By these methods it is possible to prepare branched sugars possessing a gem-hydroxy-formyl group and bearing a side chain on the more hindered side of the ring, as well as branched sugars with a gem-hydrogen-methyl group.