Photooxygenation of 5-aryl-2,4-diaminopyrimidines leading to 4-amino-1,3,5-triazin-2-yl ketones and,in the presence of sodium borohydride,to 5,6-dihyro-4(3H)-pyrimidinones

The photosensitized oxygenation of 5-aryl-2,4-diaminopyrimidines 1 in protic solvent led to the formation of the new 4-amino-1,3-5-triazin-2-yl ketones 2 in high yields. The structures of 2 were elucidated by spectroscopical means, especially by ¹³C-NMR and UV data. Photooxygenation of 2,4-diamino-5-(p-chlorophenyl)-6-ethylpyrimidine 1a under reductive conditions, e.g. In the presence of excess NaBH₄, gave 2-amino-5-(p-chlorophenyl)-t-6-ethyl-5,6-dihydro-r-5-hydroxy-4(3H)-pyrimidinone ( 4a ), the structure of which was determined by X-ray analysis. In the proposed mechanisms for both types of reactions, the dipolar ion 5 is assumed to be a common intermediate. For the new efficient synthesis of 1,3,5-triazines from 2,4-diaminopyrimidines, a 5-aryl substituent seems to be essential.