A regioselective synthesis of 5-pyrazolones and pyrazoles from phosphazenes derived from hydrazines and acetylenic esters

✍ Scribed by Francisco Palacios; Ana M.Ochoa de Retana; Jaione Pagalday

• Publisher: Elsevier Science
• Year: 1999
• Tongue: French
• Weight: 494 KB
• Volume: 55
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(99)00890-x

✦ Synopsis

Efficient and regioselective syntheses of l-phenyl-5-pyrazolones substituted with a phosphoranylidene group in the 3-position and of 3-alkoxycarbonyl-5-methoxy-l-phenyl pyrazoles ~e described. The key step is the formation of functionalized hydrazones by [2+2] cycloaddition reaction of phosphazenes derived from hydrazines with acetylenic esters. Subsequent cyclization of these compounds with butyl lithium affords substituted 5-pyrazolones, while their heating with acetonitrile leads to the formation of 3-alkoxycarbonyl-5-methoxy-l-phenyl pyrazoles in a regioselective fashion.