Pyrazole-4-carboxaldehydes

El-Emary and Abdel-Mohsen reported the synthesis of thiazolopyrimidines 12 as depicted in Scheme 4. Equimolar quantities of 1,3-diphenyl-lH-pyrazole-4-carboxaldehyde, ethyl cyanoacetate and thiourea were refluxed to yield pyrimidinethione derivative 11. This thione was cyclized to thiazolopyrimidines 12 upon reaction with chloroacetic acid and benzaldehyde [22],... 

N-[3 -(4-Methy Iphenyl)-1 -phenyl-1 H-pyrazol-4-methylidene] -cyanoacetic acid hydrazide 154 was synthesised in an excellent yield by condensing 3-(4-methylphenyl)- -phenyl-lH-pyrazole-4-carboxaldehyde with cyano-acetic acid hydrazide. This intermediate was converted to the 4-amino-3-aryl-5-[3-(4-methylphenyl)-1 -phenyl-1 H-pyrazol-4-methylidenehydrazinocarbonyl] -thiazole-2(3H)-thiones 155 (Scheme 72), following the method described by Gewald, it involved the reaction of the cyanoacetic acid hydrazide derivative 154 with sulphur and the appropriate aryl isothiocyanate in the presence of triethylamine as a basic catalyst. Cyclisation of 145 to the 3-aryl-6-[3-(4-methylphenyl)-l-phenyl-1 H-pyrazol-4-methylideneamino] -2-thioxo-2,3 -dihydrothiazolo [4,5 -djpyrimidin-7(6H)-ones 156 was achieved by heating the former with a mixture of triethyl orthoformate and acetic anhydride (1 1) [4],... 

Cyclocondensation routes also provide access to pyrimidines. 2,3-Disubstituted pyrido[2,3-/i]-quinazolin-4(3//)-ones are obtained via cyclocondensation of 5-aminoquinoline-6-caiboxylic acid with acid chlorides <02SC235>. 5,6,8-Trialkyl-7-methoxy-2-aminoquinazolines are obtained from 1,3-dimethoxybenzenes via cyclocondensation of intermediate dihydrobenzenes with guanidine carbonate <02TL3295>. Diastereoselective intramolecular hetero Diels-Alder cyclization of a pyrazole carboxaldehyde condensed onto 1,3-dimethylbarbituric acid (101) gave polycyclic heterocycle 102 <02T531>. An efficient one-step synthesis of cyclobutene-annelated pyrimidinones 103 from methyl 2-chloro-2-cyclopropylideneacetate and amidines has been... 

Oxidation of the pyrazole carboxaldehydes 294 using potassium permanganate in aqueous pyridine gave satisfactory yields of the carboxylic acids 295 (Equation 56) <2001CHE467>. Condensation of AT-alkylpyrazole-4-carbaldehyde 296 with 2,3-bis(hydroxyamino)-2,3-dimethylbutane sulfate, then sodium periodate oxidation of 1,3-dihydroxyimi-dazolidine 297 afforded pyrazolyl nitronyl nitroxides 298 (Scheme 26) <2001ARK55>. Another approach to... 

Hydrazones are also useful substrates in the preparation of pyrazoles. Reaction of N-monosubstituted hydrazones with nitroolefins led to a regioselective synthesis of substituted pyrazoles <060L3505>. lf/-3-Ferrocenyl-l-phenylpyrazole-4-carboxaldehyde was achieved by condensation of acetylferrocene with phenylhydrazine followed by intramolecular cyclization of the hydrazone obtained under Vilsmeier-Haack conditions <06SL2581>. A one-pot synthesis of oxime derivatives of l-phenyl-3-arylpyrazole-4-carboxaldehydes has been accomplished by the Vilsmeier-Haack reaction of acetophenone phenylhydrazones <06SC3479>. 

Table 27. Selected examples of correlation between observed and calculated UV transitions (Del Bene and Jaffe). (Other studied compounds include benzene, pyridine, 1,2-diazine, 1,3-diazine, 1,4-diazine, cyclopentadienide ion, pyrazole, imidazole, 2-pyrrole-carboxaldehyde, furfural, benzonitrile, nitrosobenzene, phenol, phenoxide ion, pyridinium ion, 1-hydroxy-pyridinium ion, 2-cyano-pyridine, 3-cyano-pyridine, 4-cyano-pyridine, 2-amino-pyridine, 3-amino-pyridine, 4-amino-pyridine.)...

The use of 1,2-disubstituted hydrazine hydrochlorides with / -keto esters seems to work well under milder conditions. The condensation of 1,2-dimethyl- or 1,2-diethylhydrazine hydrochlorides 63a,b with methyl 2-(4-fluorophenyl)-3-[2-(methylthio)pyrimidin-4-yl]-3-oxopropanoate 62 required heating under reflux in ethanol to give pyrazol-3-ones 64a,b (05BMCL2285) (Scheme 15). The /i-keto ester 62 was synthesized by coupling methyl (4-fluorophenyl)acetate 60 with 2-(methylthio)pyrimi-dine-4-carboxaldehyde 61 in tetrahydrofuran with LDA at —78 °C, followed by chromium(VI) oxide oxidation. 

The fluorescence quantum yields of pyrene-1-carboxaldehyde in water and methanol are 0.98 and 0.07/ an effect attributed to solvent effects on 7c,n and n,n states. Cycloaddition reactions of 1-naphthonitrile to 1,2-dimethyl-cyclopentene are attributed to both and Lj, states.It is pointed out that although dual fluorescence is known, this is the first example of divergent reaction from two nearly isoenergetic singlet states. An analysis of the u.v. spectra of some acyl pyridines, including a theoretical examination of the molecular geometry, and excited states of bipyrimidine compounds have also been made. Photo tautomerism and the fluorescence of the cation of 4-amino-pyrazole[3,4-iflpyrimidine, an analogue of adenine, has been published by Wierzchowski et Intramolecular heteroexcimer formation in... 

Biradar and Sasidhar (2011) reported a new series of novel indole analogs via Knoevenagel condensation and evaluated their in vitro antioxidant and cytotoxin activities using three tumor cell lines. 2,5-Disubstituted indole-3-carboxaldehydes undergo NH OAc catalyzed Knoevenagel condensation with barbiturates, thiazoli-dine-2,4-dione and 3-methyl-lH-pyrazol-5(4H)-one in solvent-free microwave-assisted reaction. 

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