Acyl-3,5-pyrazolidinediones

Owing to the active hydrogen atoms at C-4 in 3,5-pyrazolidinediones various substitutions at C-4 can be accomplished. Reaction with acid chlorides in the presence of aluminum chloride gives 4-acyl-3,5-pyrazolidinediones.919,976 However, if two groups are already present at C-4, the enolic form of the dione is acylated on the oxygen atom to give 3-acyloxy-2-pyrazolin-5-ones.998 Treatment of 3,5-pyrazolidinediones with nitrous acid gives nitrosation at C-4.976 The nitroso... 

The structure of 4-acyl-3,5-pyrazolidinediones has been studied by use of infrared absorption spectra.919 These studies indicate that one nuclear oxygen exists in its enolic form and the hydrogen is bonded to acyl oxygen in a chelate ring (XLVIII). These compounds are listed... 

The preparation of 4-acyl-3,5-pyrazolidinediones by acylation of 3,5-pyrazolidinediones has already been discussed in Section 2. 

One method of preparing acyloxy-2-pyrazolin-5-ones has already been mentioned (eq. 159). The second method is acylation of 3,5-pyrazolidinediones having no N-2 substituent (eq. 162). The acylations... 

TABLE XLVIII. 3,5-Pyrazolidinediones. Acyl on Nitrogen and Oxygen, Nitrogen, and Halogen Substituents ... 

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