Benzimidazoles pyrazolo

Phenyl-5-pyrazolo)-benzimidazole allgemeine Arbeitsvorschrift206 Einc Mischung von 1,0 g (4,0 mmol) 5-(2-Amino-anilino)-3-phenyl-pyrazol (R1 = H) bzw. 1,0 g (3,6 mmol) 5-(2-Amino-4,5-dimethyl-anilino)-3-phenyl-pyrazol (R1 = CH3) werden mit 5 ml Orthocarbonsaure-triethylester in Xylol 2 h am RiickfluB erhitzt. Nach dem Abziehen des Losungsmittels i. Vak, crhalt man ein Ol, das bei Zugabe von kaltem Diethylether kristallisiert. Die Produkte werden durch Umkristallisieren aus Ethanol gercinigt. 

Nitrogen Systems.—A review on the synthesis of pyrrolo[l,2-a]indoles (754) and related systems has appeared. Treatment of azobenzene (755) with 2,6-dimethylphenyl isocyanide (756) in the presence of dicobalt octacarbonyl yields a mixture of the imino-indazoline (757) and the indazolo-indazole (758)." Heating 5-amino-l-o-chlorophenyl-pyrazoles (759 R = CN or C02Et) in DMF in the presence of copper oxide yields the pyrazolo-benzimidazoles (760)." ... 

However, there are differences between o-phenylenediamine and 4,5-diaminopyrazoles in the synthesis of [5.5] systems. For example, the formation of pyrazolo[3,4-d]-[l,2,3]triazole (550) is similar to that of benzotriazole, but all attempts to extend the synthesis of benzimidazoles to the preparation of the imidazo[4,5-c]pyrazole system (551) have failed (78TH40400). 

Tile existence of pyrazolo[l,5-n]benzimidazole in form 101a in DMSO-dg has been established by NMR spectroscopy (77ORM508). 

A derivative of 163, 3-(2-morpholinoethylthio)[l,2,4]triazino[5,6-fo]indole dihydrochloride, is used as a thrombolytic (91URP1672373). Derivatives of the pyrazolo[5,l-c][l, 2,4]tria-zines were used as a constituent of silver halide color photographic supported material, which showed good color reproducibility [91JAP(K)03/291649]. The protective action of [l,2,4]triazino[4,3-a]benzimidazoles as corrosion inhibitors was studied (91MI8). 

Substituted anilinopyrazoles 244 were oxidized by lead(rv) to give intermediate pyrazolyl radicals 245, which underwent cyclization reaction with the formation of pyrazolo[l,5-tf]benzimidazoles 246 (Equation 107) <1994CB1729>. 

Acetic anhydride-promoted ring-closure reaction of 2-phenylimino-thiazoles 259 and 2-amino-benzoimidazolium salts 261 give the corresponding imidazo[2,l+]thiazolium 260 and imidazo[l,2- ]benzimidazole 262 compounds (Equations 114 and 115) <1997CHE728, 1999PCJ361 >. A similar cyclocondensation was reported for the elaboration of pyrazolo [l,5- ]benzimidazoles <2004RJ0221>. 

Examples of syntheses in which the heterocyclic ring is generated by cyclization of an exocyclic amine to an electrophilic carbon atom include the preparation of triazolo[4,3-6]triazoles (137) by elimination of alkanethiol from guanidine derivatives 136137 (cf. 132 - 133), and many examples (mostly in patents) of pyrazolo[l,5-a]benzimidazoles prepared according to Eq. (18).138-142... 

Several other classes of heterocyclic compound have been identified as alternatives to 2-pyrazolin-5-ones. Both the pyrazolo[2,3-a]benzimidazole (53) (59GEP1070030) and the pyrazolo[3,2-c]-s-triazoles (54 A, B = alkyl, aryl) (77JCS(P1)2047) give magenta dyes with low blue absorption. 

The ability to oxidize to a corresponding hydroxyl-containing heterocycle is typical for dihydro derivatives of pyrazolo[l,5-a]pyrimidines 331 and pyri-mido[l,2- ]benzimidazoles 333. Simply dissolving these compounds in CHC13, DMF and alcohols at ambient conditions produces compounds 334 and 336 as major products together with heterocycles 340 and 342 (in some cases the latter products were not observed) [168, 293]. It is interesting to note that compounds 334-336 have a very high resistance to the action of... 

An interesting approach for the synthesis of some fused pyrimidines has been reported by Shaaban [102] via reaction of 4,4,4-trifluoro-l-(thien-2-yl)butane-1,3-dione in the presence of triethylorthoformate with 5-aminopyrazole or 1,2,4-aminotriazole or 2-aminobenzimidazole under microwave irradiation. The resulting trifluoromethyl derivatives of pyrazolo[l,5-a]pyrimidine 56, l,2,4-triazolo[l,5-a] pyrimidine 57 and pyrimido[l,2-a]benzimidazoles 58 were obtained in excellent yields and purity (Scheme 42). 

AMI semiempirical calculations have shown that, as far as tautomerism is concerned, there is a structural relationship between jS-dicarbonyl compounds and NH-pyrazoles, and in a wide variety of NH-pyrazoles studied " the most stable tautomer was found to be that having the largest single-bond character between the C(3)—C(4) bond. The problem of proton transfer in NH-pyrazole crystals has been subjected to a detailed theoretical study, while a study of the tautomerism of 2-aryl and 2-heteroaryl derivatives of benzimidazole has indicated that tautomerism takes place by the intermolecular relay of protons between stacked molecules. The first report of the stable co-existence of two different histidine tautomers in one peptide crystal structure has appeared. Ab initio calculations have been used to study the tautomerism of both histamine and pyrazolo[3,4-i/]pyridazine in the gas phase and in aqueous solution, and a theoretical study of the NH tautomerism in free-base porphyrin has been undertaken. ... 

A number of heterocycles with bridged head nitrogen such as pyrazolo[l,5-a]pyrimidines 64, triazolo[l,5-a]pyrimidines 65, pyrimido[l,2-a]benzimidazole 66 and pyrimido-pyrazolo[3,4-6]pyridines 67 have been prepared. ... 

Other studies (see, e.g., ref. 187c and references cited therein) have revealed that, in systems containing only O and N as heteroatoms, the azide form 184 is usually the only isomer observable in solution or in the solid state, whatever the position of the heteroatoms. Recent work has shown that the tetrazole forms are predominant in systems containing only nitrogen as the heteroatom in two special cases. If a proton is removed from the azide (e.g., 305), the anion 306 cyclizes to the tetrazole 306b. The cyclized form is likewise formed from the anions of azido-indazoles, -imidazoles, and -benzimidazoles but cycliz-ation is only partial with s-triazoles and negligible with tetrazoles. It is possible to trap the cyclized anions (e.g., 306b) by methylation - (Section IV,C,2) and obtain stable pyrazolo[l,5-rf]tetrazoles, 307 and 308. 

Derivatives of various systems are patented as azo dyes pyrazolo-[ 1,5-a]benzimidazoles, isoindolo[2,1 -o [benzimidazoles, ... 

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