3- Pyrazolin-5-ones Mannich reaction

Pyrazolones show a great variety of reactions with carbonyl compounds (B-76MI40402). For instance, antipyrine is 4-hydroxymethylated by formaldehyde and it also undergoes the Mannich reaction. Tautomerizable 2-pyrazolin-5-ones react with aldehydes to yield compound (324) and with acetone to form 4-isopropylidene derivatives or dimers (Scheme 8 Section 4.02.1.4.10). 

As would be expected, 2-pyrazolin-5-ones undergo the Mannich reaction readily (eq. 40).1098... 

The vast majority of reactions undergone by 3-pyrazolin-5-ones occur at the 4-position. These pyrazolinones react by direct substitution, very much as do activated benzene rings. Such reactions as halogenation, nitrosation, sulfonation, acylation, the Mannich reaction and many others give 4-substituted-3-pyrazolin-5-ones. 

Mannich reaction using primary amines, when applied to 3-pyrazolin-5-ones, forms bispyrazolinones.945 Two more preparations of such compounds are shown in eqs. 146 and 147. 

Dimethyl-l-phenyl-5-oxo-3-pyrazolin-4-carboxaldehyde reacts with 2,3-dimethyl-l-phenyl-3-pyrazolin-5-one to give tris(2,3-dimethyl-I-phenyl-5-oxo-3-pyrazolin-4-yl)methane.107 Mannich and Krosche946 have treated 2,3-dimethyl-l-aryl-2-pyrazolin-5-ones with hexamethylenetetramine to give compounds of the type shown in eq. 241. The aryl groups were phenyl and p-tolyl. The reaction of 2,3-... 

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