5- Amino-6-phenyl-1,2,4-triazine 1 -oxide

The methoxy group is replaced in the reaction of 3-methoxy-5-phenyl-1,2,4-triazine 1-oxide 46 with ammonia, resulting in 3-amino-5-phenyl-1,2,4-triazine 1-oxide 47. The treatment of 3-methoxy-1,2,4-triazine 1-oxide 20 with hydrazine leads to 3-hydrazino-1,2,4-triazine 1-oxide 48 (71JOC787). 

When 5-methylthiosemicarbazide is used instead of amidrazone, 3-amino-1,2,4-triazine 4-oxides can be obtained. In this way 3-amino-5-methyl-6-phenyl-1,2,4-triazine 4-oxide 138 was synthesized from isonitrosopropiophenone [52CIL907, 89IJC(B)556]. 

In a similar reaction, 2-(o-nitrophenyl)ethylamine (100) may be reduced in an ammonia buffer to the hydroxylamine and oxidized to the nitroso derivative, which condenses with the amino group to a dihydrocinnoline.160,161 It is also possible to prepare dihydrobenzo-l,2,3-triazinones on reduction of o-nitrobenzhydrazide, followed by oxidation of the hydroxylamine to a nitroso group, and 3-phenyldihydrobenzo-l,2,3-triazine (101) from N-phenyl-(V-(o-nitrobenzyl)hydrazine (100) in an analogous way161 [Eq. (78)]. 

The examples shown are illustrative of the many easy nucleophilic additions to the polyaza-azines both 3-phenyl-l,2,4,5-tetrazine and 1,3,5-triazine itself add ammonia and simple amines (contrast the requirement for hot sodamide (Chichibabin reaction) for pyridine (8.3.1.2)) and thus amino and alkyamino derivatives can be obtained via oxidative trapping with permanganate. 

Methyl-,242 3-phenyl-,450 or 3-amino-l,2,4-benzotriazine 1-oxide or -2-oxide afford benzo-triazoles 4 when treated with sodium hydroxide377 The same reaction is observed for pyrido-[2,3-e]-l,2,4-triazin-3-amine or pyrido[4,3-e]-l,2,4-triazin-3-amine 1-oxide in sodium hydroxide affording the corresponding products in 77 and 40% yield, respectively.370 379... 

Oxidation of 4,6-diphenyl- or 4,6-bis(4-chlorophenyl)-l,3,5-triazin-2-amine with Caro s acid at a temperature below 5 °C gives 4-amino-6-phenyl- or 4-amino-6-(4-chlorophenyl)-l,3,5-triazin-2-ol 1,3,5-trioxide 1, respectively, in varying yields. The 4-cblorophenyl derivative, however, needs to be heated up to 18-20°C for 20 minutes. If the temperature during the oxidation reactions rises above 35 C, complete decomposition of the triazine is observed.1... 

The initial product 2 loses N2 in a retro-DiELS-Alder reaction forming the 3,4-dihydropyridine 3, which aromatizes giving the pyridine derivative 4 by elimination of amine or alcohol. The geometry of the transition state of this [4+2] cycloaddition with inverse electron demand follows from the reaction of 3- or 6-phenyl-1,2,4-triazine 5 or 8 with enamines of cyclopentanone. It is apparently influenced by the secondary orbital interaction between the amino and phenyl groups. 3-Phenyl-1,2,4-triazine 5 favours the transition state 11. It leads first to the 3,4-dihydropyridine 6 which, on oxidation followed by a Cope elimination, affords the 2-phenyldihydrocyclopenta[c]pyridine 7. However, 6-phenyl-1,2,4-triazine 8 favours the transition state 12 leading to 3,4-dihydropyridine 9. Elimination of amine yields 5 -phenyldihydrocyclopenta[c]pyridine 10 ... 

As for direct amination of electron-deficient heteroaromatic A-oxides, the combination of liquid ammonia and potassium permanganate is known to be a very effective system for such type of C-H functionalizations. It has been reported that 6-phenyl-l,2,4-triazine-4-oxide can easily be aminated in liquid ammonia on treatment with potassium permanganate to give 5-amino-6-phenyl-l,2,4-triazine 4-oxide (Scheme 23) [49]. 

Phenyl-l,2,4-triazine (5) leads (via transition state 11) to the 3,4-dihydropyridine 6, which (after oxidation and Cope elimination) affords the 2-phenylcyclopenta[c]pyridine 7 6-phenyl-l,2,4-triazine (8) leads to the 3,4-dihydropyridine 9 (via transition state 12) and (after amine elimination) to 5-phenylcyclopenta[c]pyridine 10. These results indicate that product formation is decisively influenced by secondary orbital interactions between the amino and phenyl groups in the transition states preceding cycloaddition. 

Benzo[2,l ]thiazolo[2,3-c][l,2,4]triazines [CsNS-CsNs-C ].—Oxidative cyclization of 3-(o-amino-aryl)-2-imino-4-phenyl-AMhiazolines (117) with A -bromo-succinimide gives the corresponding 9/f-benzo[2,l-c]thiazolo[2,3-c][l,2,4]-triazine. ... 

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