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
✍ Scribed by J. M. J. Tronchet; Melle F. Perret
- Publisher
- John Wiley and Sons
- Year
- 1972
- Tongue
- German
- Weight
- 835 KB
- Volume
- 55
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
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.