3- Aminopyrido triazine

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). 

Two types of addition to pyrimidine bases appear to exist. The first, the formation of pyrimidine photohydrates, has been the subject of a detailed review.251 Results suggest that two reactive species may be involved in the photohydration of 1,3-dimethyluracil.252 A recent example of this type of addition is to be found in 6-azacytosine (308) which forms a photohydration product (309) analogous to that found in cytosine.253 The second type of addition proceeds via radical intermediates and is illustrated by the addition of propan-2-ol to the trimethylcytosine 310 to give the alcohol 311 and the dihydro derivative 312.254 The same adduct is formed by a di-tert-butyl peroxide-initiated free radical reaction. Numerous other photoreactions involving the formation by hydrogen abstraction of hydroxyalkyl radicals and their subsequent addition to heterocycles have been reported. Systems studied include 3-aminopyrido[4,3-c]us-triazine,255 02,2 -anhydrouri-dine,256 and sym-triazolo[4,3-fe]pyridazine.257 The photoaddition of alcohols to purines is also a well-documented transformation. The stereospecific addition of methanol to the purine 313, for example, is an important step in the synthesis of coformycin.258 These reactions are frequently more... 

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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