Dérivés C-glycosyliques : Partie XII. Élaboration de cycles furoxannes, isoxazoles et 2-isoxazoline par l'intermédiaire d'oxydes de nitrile dérivés de sucres

Abstract

Treatment with a base of hydroxymoyl chlorides derived from sugars led to the corresponding unstable nitrile oxides which, in the absence of nucleophilic or dipolarophilic reagents, dimerize into furoxans. When nitrile oxides are formed in the presence of an excess of acetylenic (or olefinic) dipolarophilic reagents, they give 1,3-dipolar cycloaddition reactions with the formation of the corresponding 3-glycosylisoxazoles (or -2-isoxazolines). The action of nucleophilic reagents such as the alkaline cyanides or ethylmagnesium bromide allows the elongation of the sugar chain by one or two carbon atoms, respectively. The action of ethynylmagnesium bromide on these nitrile oxides gave a mixture of two compounds: an α-ethynyloxime and a 3-glycosylisoxazole; in alkaline medium the former compound can undergo cyclization and transformation into the latter, thus allowing deuterium labeling of that compound.