3-Aminopyrido -1,2,4-triazine 1 -oxides

UV irradiation of 3-aminopyrido[4,3-e]-1,2,4-triazine 1-oxides 7 or 1,2,4-triazine 4-oxides 8 leads to deoxygenation, i.e., loss of the 7V-oxide function resulting in the corresponding 3-aminopyrido[4,3-e]-1,2,4-triazines 9 and 1,2,4-triazines 10 (76ACH327, 76LA153). At the same time, UV irradiation of the 1,2,4-triazine 4-oxides unsubstituted at the 5 position proceeds as a ring contraction to form triazoles 11 (76LA153). 

The reaction of 4-methoxy-3-nitropyridines 129 with guanidine under similar conditions results in 3-aminopyrido[3,4-e]-l,2,4-triazine 1-oxides 130 (76MI). 

Conversion of the triazine 1-oxide (54a) to 3-aminopyrido[2,3-e]-l,2,4-triazine (58) can be achieved by reduction to the dihydro triazine (57) followed by oxidation using K3Fe(CN)6. 3-Aminopyrido[2,3-e]-l,2,4-triazine (58) is obtained in an overall yield of 57% (Scheme 2) <62JOC2504>. 

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