Acyloxy-2-pyrazolin-5-ones

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... 

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... 

A variety of 4-amino-5-alkoxy- and acyloxy-l,3-disubstituted-pyrazoles have been treated with alkylating agents such as alkyl halides to give 4-dialkylamino-3-pyrazolin-5-ones.525 There is a simultaneous alkylation of ring nitrogen and extranuclear nitrogen. 

Acylation of 2-pyrazolin-5-ones leads to 4-acyl-2-pyrazolin-5-ones. This has been done by treatment with aromatic acid chlorides110 and with ethyl oxalate in the presence of potassium. A modification of this procedure is acylation of 2-pyrazolin-5-ones to give 4-acyl-5-acyloxy-pyrazoles 591,977 or 2,4-diacyl-3-pyrazolin-5-ones1058 followed by hydrolytic removal of the A-acyl or O-acyl groups. The 4-acyl compounds can also be prepared by hydrolysis of their Schiff bases as shown in eq. 215. 

TABLE XXI. 3-Pyrazolin-5-ones. Alkoxy, Aryloxy, Acyloxy, and Alkylthio Substituents... 

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