6- Phenyl-1,2,4-triazine- 1-oxide, oxidative amination

When 3-phenyl-l,2,4-triazine (411) reacts with the enamine (406), orientation B is followed. In this case the 3,4-dihydropyridine (412) is formed and is isolated. Elimination of the amine directly is unfavourable, because of the cis orientation, and transfer of the proton to the pyridine nitrogen is impossible. Oxidation to the (V-oxide (413) and Cope elimination affords the condensed pyridine (414) (78UP21900). 

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. 

---