Dérivés C‐glycosyliques VIII. Synthèse de C‐glycosyl‐3‐pyrazoles à partir d'une nitrilimine dérivée de l'anhydro‐2,5‐D‐ribose. Compétition entre cyclo‐additions dipolaires‐1,3 et cyclisations non concertés

Abstract

Several 3‐(2,5‐anhydro‐ribosyl)‐pyrazoles of potential medicinal interest have been synthesized by reacting alkynes or alkynylmagnesium bromides with the p‐nitrophenylhydrazone of 2,5‐anhydro‐ribonyl bromide. From a mechanistic standpoint, it has been shown that the sugar‐nitrilimine used in these studies reacts more readily as an electrophile than as a dipole. Thus, the hydrazonyl bromide gave exclusively the corresponding phenylethynylhydrazone when treated with phenylethynylmagnesium bromide and led to a 1:1 mixture of phenylethynylhydrazone and pyrazole when reacted with phenylacetylene. This proves that nucleophilic additions onto nitrilimines are much faster than Huisgen's 1,3‐dipolar cycloadditions.