Phosphorus oxychloride, reaction with 2-pyrazolin-4-ones

The reaction of 2-pyrazolin-5-ones with phosphorus oxychloride to give 5-chloropyrazoles (eq. 43) is a very general one.51 307 985 992 1003-1205... 

As shown in eq. 3 (p. 9) the reaction of acyl arylhydrazines with jS-ketoesters forms 2-aryl-3-pyrazolin-5-ones.679,849,984,988,1001 The aeyl group is lost in the cyclization and these products have no N-l substituent. Formyl-, acetyl- and benzoylhydrazines may be used. This is a very frequently employed method for preparation of 2-aryl-3-pyrazoIin-5-ones. The condensing agents generally used have been phosphorus trichloride, phosphorus oxychloride and phosphorus penta-chloride. A modification of this, also mentioned earlier, has been the condensation of a symmetrically substituted hydrazine with a j8-ketoester to give l,2-disubstituted-3-pyrazolin-5-ones.54,370 The sub-... 

The reaction of phosphorus oxychloride with 3-pyrazolin-5-ones is rather similar to the reaction with 2-pyrazolin-5-ones in that oxygen is replaced by halogen. In those cases in which there is no substitution at N-l and aryl substitution occurs at N-2, chloropyrazoles are formed,... 

The oxo group in 2-pyrazolin-4-ones reacts as a hydroxyl group, forming acetates,286 benzoates1644 and urethanes.1644 Reaction of 2-pyrazolin-4-ones with phosphorus oxychloride results in replacement... 

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