2- pyrazol-3-one, reaction with

Alkynyl ketones can be formed from addition of alkynyllithium or Grignard reagents to phthalimides and then the products converted into pyrazoles by reaction with hydrazines. For example, A -alkyl-substituted phthalimides 633 were easily transformed to mono-, di-, or trisubstituted pyrazoles 634 via a one-pot addition/decyclization/cyclocon-densation process (Equation 131) <2002J(P1)207>. A -Alkyl-substituted phthalimides 635 were easily converted into di-, tri-, and tetrasubstituted pyrazoles 636 via a one-pot addition-decyclization-cyclocondensation process (Equation 132) <2003H(60)2499>. 

One of the reactions is projected in that part of the Kohonen network where mostly reactions leading to the preferred regioisomer pyrazole were projected. The other reaction was projected in neuron (7,7), which lies in a region where reactions with low yield are projected. 

There are two methods for the introduction of a hydroxyalkyl group at position 5 of the pyrazol-3-one ring. Schmidt and Zimmer converted furanediones 258a-k into arylmethylenepyrazol-3-reaction with hydrazine hydrate or methylhydrazine (83Jmechanism proposed for the reaction involves nucleophilic attack of the hydrazine on the ketone carbonyl, followed by attack on the ester carbonyl and ring opening of the... 

However, when 3,5-diphenyl-4//-pyrazol-4-one, a reagent that undergoes Diels- Alder reactions with inverse-electron demand, is used, addition of the 2,4-diene part of oxepin to one of the two C-N double bonds of the pyrazolone is observed to give 4.232... 

Different approaches towards pyrazoles have been described using microwave-accelerated cyclizations. A classical approach to pyrazoles is the cyclization of a j6-diketone with hydrazines. A series of 5-trichloromethyl-pyrazoles 58 and pyrazolium chlorides 59 were synthesized by reaction of a 4-methoxy-trihalo-3-alken-one 57 with differently substituted hydrazines (Scheme 19). The use of microwave and conventional heating for making pyrazoles gave... 

It is known that certain coumarins are transformed into 5-(2-hydroxy-phenyl)-3H-pyrazol-3-ones by reaction with hydrazines [10]. Upon appUca-tion of this method, the expected pyrazolones 25 were synthesized starting from 3-nitrocoumarins [11] as known in (Scheme 6). 

The bispyrazolodihydropyran 435 was obtained directly as a rapidly formed insoluble by-product in the reaction of 3-methyl-l-phenylpyrazol-5-one 433 with activated nitriles 434 in the presence of catalytic piperidine (Equation 117) <2000MOL746, 2000JCCS937>. It is proposed that the reaction proceeds by loss of the active methylene moiety from the initial Michael adduct, allowing attack by a second molecule of pyrazol-5-one. 

Palladium-catalyzed cyclization reactions with aryl halides have been used to synthesize pyrazole derivatives. V-Aryl-lV-(c>-bromobenzyl)hydrazines 26 participated in a palladium-catalyzed intramolecular amination reaction to give 2-aryl-2W-indazoles 27 . Palladium-catalyzed cascade intermolecular queuing-cyclocondensation reaction of o-iodophenol (28) with dimethylallene and aryl hydrazines provided pyrazolyl chromanones 29 <00TL7129>. A novel one-pot synthesis of 3,5-disubstituted-2-pyrazolines 32 has been achieved with an unexpected coupling-isomerization sequence of haloarene 30, propargyl alcohol 31, and methylhydrazine <00ACIE1253>. 

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