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Dilithiated C(α),N-phenylhydrazones were prepared in excess lithium diisopropylamide and condensed with either ethyl oxanilate, ethyl 4'-chlorooxanilate, or ethyl oxamate to give intermediates that were quenched and acid cyclized to substituted 1H-pyrazole-5-carboxamides.J. Heterocyclic Chem., 38, 691 (2001).Pyrazoles, especialy 1H-pyrazoles, have received considerable investigative attention with regard to their syntheses, and their potential for biological applications, including agriculture, and other uses. These compounds can be prepared by several methods, such as the condensation-cyclization of: β-diketones with substituted hydrazines; α,β-unsaturated carbonyl compounds with hydrazines followed by oxidation of the resulting 4,5-dihydropyrazole; nitrilimines with substituted alkynes [1]; or dilithiated hydrazones with esters, and related electrophilic reagents [2].The preparations and uses of substituted 1H-pyrazole-5-carboxamides range from simply substituted to those compounds where the other pendant groups are more complex. A favored synthetic route for 1H-pyrazole-5-carboxamides involves preparing a 1H-pyrazole-5-carboxylic acid followed by its transformation to the carboxylic acid chloride, which is then treated with an amine [3]. There are additional reports dealing with carboxylic acid amides in the 1-, 3-and 4-positions of the pyrazole ring [4][5][6]. The compounds have been studied for their biological potential, use in other syntheses, and a focus on spectral investigations.The preparation of 1H-pyrazole-, 5-propanoic or 5-butanoic acids and N-carboalkoxy-1H-pyrazoles has been demonstrated [2b-e,7], where a variety of C(α),Ncarboalkoxyhydrazones were dilithiated with excess lithium diisopropylamide, and these intermediates were condensed-cyclized with select carboxylic acid anhydrides, or more generally with a variety of esters. In related pyrazole preparation studies, polylithiated hydrazones have been condensed-cyclized with other anionic electrophiles, such as lithiated ethyl benzoylacetate [2c,8], lithiated methyl thiosalicylate [9], and lithiated hydroxybenzoate esters [2b].At an earlier time, hydroxy-pyridazinones were prepared from dilithiated C(α),N-phenylhydrazones that were condensed-cyclized with ethyl oxalate, an electrophilic reagent related to the oxanilates or oximate used during this study.[10]. Also, there are limited reports of the condensations of ethyl oxanilates or ethyl oxamate with nucleophilic reagents, such as [11] amines or amides, which were part of a synthetic sequence. The condensation of lithiated oxamates and lithiated oxanilates, which are anionic electrophiles, with anionic nucleophiles is new.During the current study, several C(α),N-phenylhydrazones 1 were dilithiated (to 2) with excess lithium diisopropylamide, followed by treatment with either lithiated ethyl oxanilate, lithiated ethyl 4'-chlorooxanilate, or lithiated (possible dilithiated) ethyl oxamate. When the resulting Cacylated intermediates were neutralized to 3 with aqueous hydrochloric acid, this was fol...

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Several 2'-phenylphenylacetohydrazides were polylithiated with excess lithium diisopropylamide, and the resulting intermediates were condensed with several aromatic esters to afford C-acylated intermediates that were not usually isolated, but acid cyclized directly to 1,4,5-trisubstituted, 1,2-dihydro-3H-pyrazol-3-ones.J. Heterocyclic Chem., 38, 695 (2001).While the preparations, reactions, and uses of 1H-pyrazoles and related heterocyclic compounds are well documented [1], investigations involving other pyrazole compounds such as 1,2-dihydro-3H-pyrazol-3-ones [2,3] have received less investigative attention. For example, a key compound to this report, 1,2-dihydro-1,4,5-triphenyl-3H-pyrazol-3-one 4, has been prepared by: (1) the fusion of 2'-phenylacetohydrazine with ethyl 2-benzoyl-2-phenylacetate [4]; or (2) by the condensation of benzoylphenyl ketene with phenylhydrazine [5]; or (3) by the reaction of diphenylcyclopropenone with excess phenylhydrazine [6]. Several additional and related alkyl, or alkyl-aryl, 1,4,5-trisubstituted, 1,2-dihydro-3H-pyrazol-3-ones have also been prepared and studied, especially with regard to their biological-health applications or use in other syntheses [7][8][9][10][11][12][13][14][15]. There is a preference to listing the structures for these molecules as 1,2-dihydro-3H-pyrazol-3-ones instead of their tautomers, 3-hydroxy-1H-pyrazoles. Both forms have been reported by investigators [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], which may indicate the differences that exist when the supporting structural data was obtained from a solution, a mull, or a crystalline form of a particular compound.Compound 1, 2'-phenylphenylacetohydrazide, a key starting material used during this study, has been used for the preparation of other pyrazole or pyrazole-related heterocyclic compounds such as methods involving variously substituted N-methyl or N-acylphenylacetohydrazides, or a condensation-cyclization of a probable carbanion resulting from deprotonation with calcium hydride followed by the addition of N, N-dimethylformamide [20-25].In recent investigations with other carbohydrazides, we polylithiated o-toluoylcarboalkoxyhydrazides (2'-(2-methylbenzoyl)hydrazinocarboxylic acid esters) with excess lithium diisopropylamide, and condensed-cyclized the polylithiated intermediates with a variety of aromatic esters. This was followed by acid cyclization of the C-acylated intermediates to afford isocarbostyrils (1(2H)-isoquinolinones) [26].One of our major strong-base multiple anion synthesis efforts has dealt with the preparation of 1H-pyrazoles and related compounds by the utilization of C(α), N-hydrazone (e.g., phenyl, benzoyl, carboalkoxy, etc.) entry compounds that were polylithiated with excess lithium diisopropylamide [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. The polylithiated intermediates were condensed with a variety of esters and other electrophilic reagents, followed by an acid cyclization of C-acylated intermediates that were not usually isolated. This...

Preparation of 3-(2-Phenylethenyl)-1H-pyrazoles from Dilithiated (3E)-4-Phenyl-3-buten-2-one Hydrazones.-The hydrazones (III) are treated with lithium diisopropylamide, and the resulting 1,4-dianions are condensed with aromatic esters (IV) followed by acid cyclization to afford the title compounds (V) in moderate to high yields.-(PASTINE, STEFAN