Novel 6-azapteridines and oxazinotriazines from bifunctional 1,2,4- triazines

Ethyl 5-amino-1,2,4-triazine-6-carboxylates 1a-b undergo condensation with aryl isocyanates 2a-b to afford the corresponding pyrimido[4,5-e][1,2,4]triazines 3a,b. Alternatively, 1a-b reacted with triphenylphosphine and hexachloroethane to afford the corresponding iminophosphoranes 6a-b, of which 6a with excess benzoyl chloride 7 afforded the 3,1oxazino[6,5-e][1,2,4]triazine 8a.