2.4- Dihydropyrazol-3-ones, synthesis

The standard route to sydnones is the cyclodehydration of iV-nitroso-P-amino acids. 2-Chloro-4,5-dihydro-13-dimethylimidazolium chloride 97 has been shown to be an excellent reagent for this conversion, as, for example, in the synthesis of 3-phenylsydnone 98 <99JOC6989>. Functional group manipulations of fused sydnones have led to the isolation of several new compounds including 99 and 100 <99H(51)1433>. 4-Acetylsydnones react with hydrazine at room temperature to give 2,4-dihydropyrazol-3-ones 101 <99H(51)95>. ... 

Attansai et al have reported the first general protocol for the preparation of polymer-bound 1,2-diaza-1,3-butadienes (93) and demonstrated their utility in the solid state synthesis of 4-triphenylphosphoranylidene-4,5-dihydropyrazol-5-ones (94) (Scheme 17). ... 

Polymer-bound 1,2-diaza-1,3-butadienes have been employed in the solid-phase syntheses of 4-triphenylphosphoranylidene-4,5-dihydropyrazol-5-ones and 4-methoxy-l//-pyrazol-5-(2//)-ones <01T5855>. Solid-phase synthesis of substituted pyrazolones 40 from polymer-bound P-keto esters 39 have been published <01EJO1631>. Solid phase cycloaddition of nitrile imines to resin-bound enamincs afforded 1,4-diarylpyrazoles after acidic cleavage <01JCS(P1)2817>. 

SCHEME 18 Synthesis of 4-I(5-hydroxy-3-methyl-l-phenyl-lH-pyrazol-4-yl)phenyl-methyl]-5-methyl-2-phenyl-l,2-dihydropyrazol-3-ones using ionic liquid as catalyst. 

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