1,2,4-Triazoles, fused

Flydrazides of the pyridopyrazine series, such as 247-249, undergo thermal cyclization to give 1,2,4-triazole-fused products (Scheme 57) C1997FA49, 2000PHA896, 2005JOC2878>. 

Several interesting 1,2,4-triazole fused-ring systems have been reported. A facile synthesis of 3,5-dihydro-677-imidazo[l,2-fc]-l,2,4-triazol-6-ones 162 was obtained by an iminophosphorane-mediated annulation <06EJ04170>. 8-Trifluoromethyl-l,2,4-triazolo[4,3- >]pyridazines 163 has been prepared from 4-trifluoromethyl-4,5-dihydropyridazin-3-one... 

Structurally unique 1,2,4-triazole fused-ring systems were reported. Parent names and references of the scaffolds are shown below. 

Triazoles Fused to Another Five-Membered Heterocycle. 285... 

Scheme 7. Preparation of the 1,2,3-triazole-fused dehydroannulenes 42 - 44 as potential cyclocarbon precursors [71]...

In yet another approach towards the synthesis of cyclocarbons by cycloreversion, Adamson and Rees [71] prepared the 1,2,3-triazole-fused dehydroannulenes 42 - 44, as mixtures of regioisomers in ca. 30 % overall yield, by oxidative Hay coupling of the protected 4,5-diethynyl-l,2,3-triazole 41 (Scheme 7). No investigations have yet been reported on the thermal or mass spectrometric [3-1-2] cycloreversions of 42-44, with loss of the triazole moieties and ultimate formation of the cyclocarbons Cis, C24, and C30, respectively. 

Triazole-fused pyridopyrimidines can be prepared by reaction of aldehydes with the substituted pyridopyrimidine 309 (Equation 106). The pyrazole-fused derivative 311 can be prepared by the reaction of the sulfonimine 310 with dimethyl acetylenedicarboxylate (DMAD) (Equation 107) <1998H(47)871>. 

Pyranopyridines. The chlorobenzopyranoquinolone 325 reacts with hydrazides to give a triazole-fused ring system, such as in compound 326. Likewise, reaction with sodium azide gives the tetrazolo-fused product 327 (Scheme 79) <2003IJB2567>. 

Triazoles fused with larger aromatic systems can be also obtained this way. Thus, in an example given in Equation (30), 2i/-phenanthro[9,10-r/l-l,2,3-triazole 1221 is obtained in 84% yield from a reaction of 3-hydroxyphe-nanthro-l,2,4-triazine 1220 with NCS <2000H(53)203>. 

Ring Synthesis of Triazoles Fused to the c-Site of Pyrimidine Ring 733... 

Synthesis of triazoles fused to the c-site of quinazole ring 737... 

Three triazole-fused oxadiazines have been synthesized during the recent period, as shown in Scheme 19. 

The synthesis of 1,2,3-triazole-fused tetracyclic compounds via intramolecular click chemsitry approach was presented (Fig. 49).65... 

When the synthesis of a heterocyclic system containing a diazole fused onto l,2,3-triazin-4-one (e.g., imidazo[4,5-i [l,2,3]tnazin-4-one (Section 10.13.9.1.l(i)) and pyrazolo[3,4-rf [l,2,3]triazin-4-one (Section 10.13.9.1.1(ii))) or 1,2,3-triazole fused onto pyrimidin-4(7)-(di)one (e.g., [l,2,3]triazolo[4,5-rf pyrimidin-4(7)-(di)one (Section 10.13.9.1.l(iv))) is required, the synthesis of the six-membered ring is the most reliable method. There are several recent accounts of six-membered annulations onto 1,2,3-triazoles to give [l,2,3]triazolo[4,5-r/ pyrimidines (Section 10.13.9.1.l(iv)), which are valuable alternatives to 1,2,3-triazole annulation using nitrosation techniques <1996CHEC-II(7)489>. 

The transformations of bis(triazole)-fused benzothiadiazepine 40 (Scheme 4) on treatment with -BuLi depended on the reaction temperature at —40°C, the sulfur extrusion occurred to afford fully aromatized bis(triazolo)quinoxaline 41, whereas at — 80°C, a seven-membered ring opening took place with formation of bis(triazolyl)benzene 42 <2002MC131>. 

Type cycloadduct 24 (Scheme 1) was obtained as the major product on cycloaddition of n-chloranil with l-ethoxycarbonyl-l/7-azepine <1982H(19)1197>. Treatment of 4-ethoxycarbonyl-5-chloro-l,2,3-thiadiazole with ethylenediamine under basic conditions occurs with heterocyclic ring opening/recyclization to form bis(triazole)-fused thiadiazepine 77 (R = COOEt) (Scheme 14). The benzo-fused analog was prepared by the similar reaction with o-phenylenediamine <1999CC2273>. 

Several examples of the conversion of 2-(acyihydrazino)azines into a triazolo-azine are mentioned on pp. 99-101 another variation on these experimental conditions is to heat the substrate in refluxing toluene to which 4-toluenesul-phonic acid monohydrate is added. The synthesis of triazoles fused at their... 

Three major routes to the v-triazole-fused ring system (38) have been published. Reaction of (195) with ) -diketones leads to the neutral product (196) (Equation (50)) <83JHC735>, whereas oxidative... 

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