1,2,4,5-Tetrazine dihydro

Table 1 Bond Distances (A) and Angles (°) in 1,2,4,5-Tetrazines, Dihydro-1,2,4,5-tetrazines, Hexahydro-1,2,4,5-...

Tetrazine-3,6-dicarboxylic acid, 1,6-dihydro-diethyl ester... 

Like lV-methyl-2-phenylbenzothiazoliiim iodide (76KGS635), the salt 19 reacts with hydrazine hydrate to give 3,6-diphenyl-l,2-dihydro-l,2,4,5-tetrazine and di(o-lV-methylaminophenyl) ditelluride (92MI1). 

Oxidation of the 2//-4a,7-dihydro derivative 15, the inverse electron-demand [4+2] Diels-Alder cycloadduct of ethyl 1 /7-azepine-l -carboxylate and dimethyl l,2,4,5-tetrazine-3,6-dicar-boxylate, with tetrachloro-l,4-bcnzoquinone furnishes the pyridazino[4.5-r/]azepine 16.112... 

The isomeric pyridazino[4,5-6]azepine 19 is obtained directly during the decomplexation of the [4 + 2] adduct 17 formed from tricarbonyl(ethyl +17/-azepine-l-carboxylate)iron and 1,2,4,5-tetrazine-3,6-dicarboxylate, with trimethylamine A-oxide.113 Surprisingly, decomplexation of adduct 17 with tetrachloro-l,2-benzoquinone yields only the dihydro derivative 18 (71 %), aromatization of which is achieved in high yield with trimethylamine A-oxide in refluxing benzene. 

Several dihydrotetrazine materials have been promoted as oxygen scavengers, including 3,6-dimethyl,1-2-dihydro,1,2,4,5-tetrazine, and the diethyl- and diphenyl-derivatives. 3,6-Dimethyl,1-2-dihydro,1,2,4,5-tetrazine is a six-sided ring with a formula H3C-CN2C-CH3NHNH its MW equals 102. Its basic reaction with oxygen is shown here ... 

Regarding the series of hetero aromatic pentacyclic compounds with three heteroatoms, an accelerated synthesis of 3,5-disubstituted 4-amino-1,2,4-triazoles 66 under microwave irradiation has been reported by thermic rearrangement of dihydro-1,2,4,5 tetrazine 65 (Scheme 22). This product was obtained by reaction of aromatic nitriles with hydrazine under microwave irradiation [53]. The main limitation of the method is that exclusively symmetrically 3,5-disubstituted (aromatic) triazoles can be obtained. 

Nitrilimines react with hydrazones of aliphatic aldehydes and ketones to yield addition products 9 which cyclise when treated with palladium charcoal at room temperature to give 1,6-dihydro-j-tetrazines 10 <96JCR(S)174>. 

Amino-1,2,4-triazole has been obtained from orthoformic ester and hydrazine hydrate in a sealed tube at 120° 1 by heating formylhydrazine at 150-210° 2-3-4 by heating N,N -diformyl-hydrazine at 160° 5 by decarboxylation of 4-amino-1,2,4-tria-zoldicarboxylic acid 6 by fusion of l,2-dihydro-l,2,4,5-tetrazine 6 and by heating l,2-dihydro-l,2,4,5-tetrazinedicarboxylic add above its melting point.4-6-7... 

Refluxing a mixture of hydrazonoyl halides 13 and heterocyclic thiones 14 in ethanol in the presence of triethylamine resulted in the formation of 3-arylazo-l,4-dihydro-l,7-disubstituted-pyrimido[l,2,-3]-l,2,4,5-tetrazin-6-ones 8. The reaction starts with the initial formation of the hydrazidine derivatives 15, which in turn undergo cyclization with the elimination of thiolate to give the desired product 8 (Scheme 1)<2004JCM399>. 

For the synthetic studies on the bicyclic 6-6 systems 1-3, with one ring junction nitrogen and five extra heteroatoms, refer to CHEC-II(1996) <1996CHEC-II(8)743>. In the studies of the newly available compounds, a one-pot procedure for the synthesis of [l,2,4]triazino-[4,3- ][l,2,4,5]tetrazine 4 derivatives is discussed below. Refluxing of hydrazonoyl halides 10 in chloroform (or ethanol) in the presence of triethylamine for 6h with either 4-amino-2,3-dihydro-6-substituted-3-thioxo-[l,2,4]triazin-5(4//)-ones 8 or 4-amino-3-methylthio-6-substituted-[l,2,4]-triazin-5(4//)-ones 9 yielded compounds 4 (Equation 1) <2000JPR342>. 

Methyl 3-acyl-l-diphenylmethyleneamino-4,5-dioxo-4,5-dihydro-l//-pyrrole-2-carboxylates 489 are formed from 488 and oxalyl chloride in good yields. Preparative thermolysis of these compounds at 130-140°C gives mixtures of dipyrazolo[l,2- l,2- [l,2,4,5]tetrazines 491 as major products and pyrazoles 492 as minor hydrolytic by-products. The intermediacy of mesoionic compound 490 is expected (Scheme 83) <2004T5319>. 

A one-pot synthesis of 3-methyl-5-aryl-4//-pyrrolo[2,3-<7]isoxazoles was performed in high yields by Sharpless epoxidation of 4-amino-3-methyl-5-styrylisoxazoles <06TL4957>. 1,2,4,5-Tetrazines were condensed with isoxazolylcyclobutanones in methanolic KOH to give conformationally restricted 6-isoxazol-5-yl-6,7-dihydro-5//-[l,2]diazocin-4-ones <06JOC2480>. 

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