Pyrazol-3-ylidene

The Peris group has looked at the influence of lmidazol-2-ylidene, imidazol-4 ylidene, and pyrazol-3-ylidene ligands on the P-alkylation of secondary alcohols... 

Only a very few 4,4 -bis(2-pyrazolin-5-ones) linked by a double bond have been prepared. The parent compound of this series, 4-(3-methyl -1 -phenyl - 5 - oxo - 2 - pyrazolin - 4-ylidene)-3-methyl-l-phenyl-2-pyrazolin-5-one (XXII-D), is known as pyrazole blue.323,807,809,816, 1090,1091 was so nameci by Knorr because of its great resemblance to indigo blue. All these compounds are strongly colored. The usual synthesis is by ferric chloride oxidation of monomeric 2-pyrazolin-5-ones (eq. 61)296,809 or by oxidation of the corresponding bis compounds... 

El tsov and co-workers (85JOU596) (Scheme 67) have proposed a mechanism for the reaction of 4-[(dimethylamino)methylidene]-pyrazol-3-one 248 with cyanide ion in the presence of dimethylacetamide followed by the addition of carbon dioxide and then acidification that gives cyano(3-oxopyrazol-4-ylidene)acetic acid 252. Addition of cyanide ion to the a,jS-unsaturated functionality of 248 affords 249 which eliminates dimethylamine to give 250. Proton abstraction from 250 gives the pyrazol-3-one salt 251, which is converted into the acid 252 by bubbling in carbon dioxide and then acidifying. The progress of the reaction up to intermediate 251 was monitored by UV and IR spectroscopy. 

Transformation of (l,3-dioxolan-2-ylidene)methylphosphonates (or phosphinates) to 5-amino-A -substituted-3-(2-hydroxyethoxy)-4-phosphono (or phosphino)pyrazoles occurs by reaction with hydrazines, R —NH—NH2 (R = CH3, CsHj, OEt) <92HCA124>. Similarly, dioxolanes (259) are transformed into 5-hydroxypyrazoles (260) by reaction with hydrazine and into pyrazolium betaines (261) by reaction with 1,1-disubstituted hydrazines <92HCA1039>. 

Mit (2-Chlor-6-phenyl-3,4-dihydro-pyrimidin-4-yliden)-malonsaure-dinitril ist die direkte Umsetzung mit Hydrazin ebenfalls moglich, wobei gleichzeitig Halogen-Substitution erfolgt443 und man erhalt 3,5-Diami-no-4- (2-hydrazino-6-phenyl-4-pyrimidyl)-1 H-pyrazol (44%). 

Methyl-2-pyridin-2-yl-2,4-dihydro-pyrazol-3-one 40 was synthesized by heating ethyl 3-oxobutanoate 5 and (lH-pyridin-2-ylidene)-hydrazine 39 in methanol containing potassium hydroxide (04IC4387) (Scheme 9). Compound 40 was used to synthesize, among others, silver complexes. 

Tetracyanoethylene has been used as an electrophile by two different groups of researchers, Junek et al. (88M993) and Elnagdi and co-workers (89LA1037) (Scheme 111). Reaction with pyrazol-3-ones 361a c was conducted in refluxing ethanol and the products 2-(3-oxopyrazol-4-ylidene)malononitriles 362a-c, usually deeply coloured, were obtained in over 80% yield. These compounds were further reacted with aliphatic, aromatic and heterocyclic amines. 

Maquestian et al. (84BSB1073) (Scheme 112) describe the reaction of pyrazol-3-ones 363a-e with ethyl 3-aminobut-2-enoate 364 as taking place in two steps, possibly because intermediate 365 is relatively stable. After initial conjugate addition, elimination of ammonia from 365 yields (E/Z) ethyl 3-(5-oxopyrazol-4-ylidene)butanoates 366a-e. 

Addition of pyrazol-3-ones 439a,b to 2-(2-oxoindol-3-ylidene)malononitrile 440 gave adduct 441 (82CL1123) (Scheme 134). 

An interesting reaction between pyrazol-3-one 62 and A,A -diphenylformamidine 576 has appeared in a patent (69GEP1800581) (Scheme 172). The reaction took place by heating these compounds in a mixture of acetaldehyde and triethylamine and gave, in excellent yield, ( /Z)-4-[3-(pyrazol-4-yl)prop-2-enylidene]pyrazol-3-one 581. The proposed mechanism suggests initial substitution and loss of aniline, addition of acetaldehyde to the a,/1-moiety of pyrazol-3-one, loss of aniline from 578 to a 3-(5-oxo-pyrazol-4-ylidene)propionaldehyde 579c, addition of a second molecule of 62 to... 

In the reaction of pyrazol-3-ones with imines, alkoxide groups have also been displaced from heterocyclic derivatives. Thus the reaction of 10-thia-8-azabenzo[a]-azulene 603 with pyrazol-3-one 62 in refluxing ethanol afforded pyrazol-3-one derivative 604 in 42% yield (73AP531). When the electrophile used was 2-n-butoxyazepine 605 reaction with 62 took a different path in the elimination step. Loss of M-butanol from adduct 606 gave 4-(azepin-2-ylidene)pyrazol-3-one 607 in 62% yield (88T3309) (Scheme 179). 

Follow-up chemistry of azetidyl ylide 94, which was obtained by hydrolysis of ylide 84, led to various pyrrolidines and pyrazoles [68]. The reaction with methyl oxalyl chloride gave a 4-triphenylphosphoranyhdene-pyrrolidine-2,3,5-trione 95, while treatment with ethyl diazoacetate afforded 4-anilido-3-triphenylphosphoran-ylidene-pyrazole-5-carboxylic acid ethyl ester 96 (Scheme 20). 

For instance, a new bidentate NHC pyrazolate ligand precursor featuring a methylene spacer between the benzimidazol-2-ylidene and the pyrazolate moieties has been used to obtain four new luminescent platinum(ii) complexes along with either phenyl-pyridine or pyridine-triazole luminophores/ ... 

Benzenaminium, 3-[(4-amino-6-bromo-5,8-dihydro-1-hydroxy-8-imino-5-oxo-2-naphthalenyl) amino]-N,N,N-trimethyl-, chloride. See Basic blue 99 Benzenaminium, 3-[(4,5-dihydro-3-methyl-5-oxo-1-phenyl-1 H-pyrazol-4-yl) azo]-N,N,N-trimethyl-, chloride. See Basic yellow 57 Benzenaminium, N,N,N-trimethyl-, hydroxide. See Tri methyl phenyl ammonium hydroxide Benzenaminium, N,N,N-trimethyl-4-((4,7,7-trimethyl-3-oxobicyclo (2.2.1) hept-2-ylidene) methyl)-, methyl sulfate. See Camphor benzalkonium methosulfate Benzenamne, 2-nitro-N-pheyl-. See 2-Nitrodiphenylamine Benzene... 

The products of the reaction of acetylenedicarboxylic acid esters with 4,5-dihydro- 1 //-pyrazole-1 -carbothioamides and 3,4,5,6-tetrahydro-2/f-1,2,4-triazepine-3-thiones have been characterized by Danilkina et by the use of NMR parameters including Vhc and couplings. In particular, the /h5C4 couplings of 5.0 Hz observed for methyl esters of (2Z)-[2-(3-methyl-4,5-dihydro-l TZ-pyrazol-1-yl)-4-oxo-1,3-thiazol-5(4//)-ylidene]ace-tic acids have provided evidence that the exocyclic double bonds in these compounds are of the Z configuration, which corresponds to the mechanism reported by the authors for the trans addition of the SH group to the triple bond in DM AD. 

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