AbstractSeveral 3‐(2,5‐anhydro‐ribosyl)‐pyrazoles of potential medicinal interest have been synthesized by reacting alkynes or alkynylmagnesium bromides with thep‐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 thanHuisgen's1,3‐dipol