2- Pyrazolin-5-ones condensation reactions

If a,j8-unsaturated ketones are condensed with 2-pyrazolin-5-ones the reaction is a Michael addition (eq. 30)686 721 resulting in alkylation. 

Aldehydes and ketones react with azolinones. The reaction between aldehydes and 2-phenyl-5-oxazolinone (131 Y = H), formed in situ from PhC0NHCH2C02H and AC2O, gives azlactones (131 Y = RCH). Similar reactions are given by 4-thiazolidinones, e.g. (132) gives (133) (79AHC(25)83), and 4-imidazolinones. In pyrazolin-5-ones the 4-position is sufficiently activated for condensation to occur with ketones in acidic media (Scheme 8) (66AH06)347). 

IV-Alkyl-substituted phthalimides 9 were easily transformed into mono-, di- or trisubslituted pyrazoles 10 via a one-pot addition/decyclization/cyclocondensation sequence <02JCS(P1)207>. 5-Silylpyrazoles can be prepared from condensation of silylalkynones with hydrazines <02T4975>. Reactions of acylated diethyl malonates with hydrazine monohydrochloride in ethanol afforded 3,4-disubstituted pyrazolin-5-ones <02T3639>. 

A number of syntheses of 2-pyrazolin-5-ones depend on the reaction of compounds, other than /3-ketoesters, substituted in the /3-position or of a,/8-unsaturated acids, esters and amides. The most frequently used unsaturated compounds are those having a triple bond in the apposition.1023,1024,1075,1548,1680 R2 can be HO,1552 RO1023,1024,1686 or H2N (eq. 8).1023,1024 A similar reaction is the condensation of ethyl... 

A reaction analogous to the condensation of amides with 2-pyrazolin-5-ones is the reaction of amidines first reported by Dains (eq. 29).348,349 This has been extended by Ogata, Tauno and Nishida1070 to vinylogs of amidines of the type C6H5NH(CH==CH)2CH=NC6H5. 

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-... 

Presumably the linking group is >NCH—N<. Bisamides of l-(amino-phenyl)-2-pyrazolin-5-ones and of 3-amino-2-pyrazolin-5-ones have been used. l-(3-Aminophenyl)-3-methyl-2-pyrazolin-5-one reacts with many aldehydes and ketones to form polymers.964 Probably condensation occurs at C-4 and the amino group. The product of reaction of p-cresol with formaldehyde has been found to react with 1-(4-hydroxy -phenyl)-3-methyl-2-pyTazolin-5-one to give a polymer that must have the aromatic and pyrazolinone rings connected by ether linkages.1269... 

The reactions undergone by 5-imino-3-pyrazolidinones are in general very similar to those of 2-pyrazolin-5-ones. The hydrogen atoms at C-4 are active and this position is the reactive center in the nucleus of these molecules. Condensation with aldehydes and ketones occurs with formation of benzylidene644,1083 or 4,4 -benzylidenebis... 

The formation of pyrylium salts from methyl(ene) ketones and 1,3-diketones, e.g., of 2,4,6-triphenylpyrylium from acetophenone and dibenzoylmethane, has an interesting counterpart in several reactions of pyrylium salts. With nucleophiles like phenylhydrazine,353 hydroxylamine,353 or benzylmagnesium chloride,178-180 2,4,6-triphenylpyrylium forms unstable 2,4-dien-l-ones or 4 -pyrans, which rearrange easily to more stable pyrazolines, isoxazolines, or 2H-pyrans on treatment with strong acids, both types of product split off acetophenone, yielding 1,3,5-triphenylpyrazole, 3,5-diphenyl-isoxazole, and 1,3-diphenylnaphthalene, respectively. These same products can be obtained directly from the above nucleophiles and dibenzoylmethane.63,354-357 The condensation of methyl(ene) ketones with 1,3-diketones yielding pyrylium salts can, therefore, be considered reversible in a certain sense. 

Condensation of 140 with 3-methyl-l-phenyl-pyrazolin-5-(4//)-one was carried out on alumina support and under solvent-free conditions using MWI to give 3-methyl-4-[(chromon-3-yl)methylene]-l-phenyl-pyrazolin-5-(4//)-ones 142 in 59-87% yields within 2 min (Scheme 28). The same reaction in refluxing dioxane using a catalytic amount of triethylamine required 45 min to give lower yields (02SC497). 

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