1,2,4-Triazole, 4- 2-pyridyl

Heating 4-oxo-4//-pyrido[l, 2-n]pyrimidine-3-diazonium tetrafluorobo-rate and its 8-methyl derivative in alcohol at 60-90 °C for 15 min to 5h gave alkyl 1-(2-pyridyl)- and 1-(4-methyl-2-pyridyl)-l//-1,2,3-triazole-4-carboxylates (00H(53)1793). 

The complex [Ir(ppy)2(dpt-NH2)]PF6 (175), dpt-NH2 4-ami no-3,5-bis(2-pyridyl)-477-1,2,-4-triazole, (176), has been synthesized and characterized319 A reversible, one-electron oxidation of (175) is assigned to removal of an electron from an Ir (/--based orbital. (175) luminesces at room temperature and 77 K. The complex (175), when immobilized in a polymeric matrix, acts as an... 

The synthesis of a series of 2-pyridyl-substituted 1,2,4-triazoles was achieved from methyl 4-cyanobenzimidate 88 by reaction with the appropriate acid chloride and hydrazine via the unstable iV-aroyliruidatc intermediate. For example, reaction of 88 with 4-methoxybenzoyl chloride gave the imidate 89, subsequent reaction of which with pyridylhy-drazines 90a and 90b gave 1,2,4-triazoles 91a and 91b (Equation 33) <2004BMC2013>. 

Ejection of dinitrogen from the triazoline adducts to form the related aziridines was promoted by ultraviolet irradiation (300 nm, benzene) and usually proceeded in excellent yield. An exception was found in the irradiation of the triazoline substrate 59, where cleavage of the cyclobutane ring occurred as the dominant reaction pathway to form the pyridazino norbomadiene 61 (and secondary photoproducts derived therefrom), together with the triazole-4,5-diester 62. A role for the pyridazine ring and the 2-pyridyl substituents in stabilising the diradical intermediate 60 has been proposed for this abnormal outcome (Scheme 8). 

Pyrazol-3-yl)pyridine 4-(2 -Pyridyl)l,2,4-triazole Room temperature R-substituted triazole in 4-position Spin crossover... 

Just as with nondoped red fluorescent dyes, nondoped phosphorescent iridium complexes consisting of two chelating phenyl-substituted quinazoline and one (2-pyridyl) pyrazolate or triazolate have recently been reported by Chen et al. (278-280) (Scheme 3.88) [308]. All of these complexes exhibited bright red phosphorescence with relatively short excited state lifetimes of 0.4-1.05 ps. PHOLEDs fabricated using the compounds A and B with relatively... 

Ethyl 2-(3-pyridyl)-7-hydroxy-1,2,4-triazolo[ 1,5-a ]pyrimidine-6-car-boxylate was obtained in the reaction of 3-amino-5-(3-pyridyl)-1,2,4-triazole and EMME in boiling acetic acid for 4 hr in 22% yield [89IJC(B)242]. 

Jain and Handa reported [82IJC(B)732] that the mode of ring closure may depend critically on the 5-substituent of the triazole. 3-Mercapto-5-(4 -pyridyl)[l,2,4]triazole 143 was reacted with phenacyl bromides to give 144, which on treatment with PPA resulted in the formation of thiazolo[2,3-c][l,3,4]triazoles 145. The structure of 145 [R = (4-Cl)C6H4] was proved by an independent synthesis starting with isonicotinyl thiosemicarbazide. 

Synthesis of benzo[c]furans and isoindoles (181) is also possible by the addition of benzyne to the respective monocycles (178), followed by reduction (179 — 180) and pyrolysis. In an alternative procedure, (179) is reacted with 3,6-bis(2-pyridyl)-l,2,4,5-tetrazine, which affords (181) under far less vigorous conditions via a retro Diels-Alder reaction of the intermediate (182). 4-Phenyl-1,2,4-triazoles pyrolyze to form isoindoles (Section 3.4.3.12.2). 

Artemov and Shvaika treated a number of 2-aryl-l,3,4-oxadiazole-5(4//)-thiones (293) with methylhydrazine (R = Me) and obtained a mixture of 1-methyl-1,4-dihydro-1,2,4,5-tetrazine-6(5/f)-thiones (294) and 4-methylamino-l,2,4-triazole-3-thiones (295 R = Me) (71KGS905). A similar reaction was reported by Konig and his coworkers, who treated 5-(4-pyridyl)-l,3,4-oxadiazole-2-thione (293 Ar = py) with hydrazine (R = H) and obtained a compound which was either the l,2,4,5-tetrazine-6-thione (294 R = H) or the 4-amino-l,2,4-triazole-3-thione (295 R = H) (54CB825,56GEP953801). 

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