Condensed 1,2,4-Triazines: Synthesis of 5-Benzyl-5H-imidazo(4,5-e)-1,2, 4-triazine 1-Oxides (9-Benzyl-6-azapurine 6-Oxides).

A number of 5-benzyl-5H-imidazo[4,5-e]-1, 2, 4-triazine 1-oxides, bioisosteric isomers of antiviral 9-benzylpurines, have been prepared. Oxidation of 6-amino-5-benzylamino-3-methylsulfanyl-1, 2, 4-triazine 1 with excess of m-chloroperbenzoic acid afforded 6-amino-5-benzylamino-3-methylsulfonyl-1, 2, 4-triazine 1-oxide 2 in 75% yield. The 3-methylsulfonyl group, which is a good leaving group, has been replaced with various nucleophiles to give 3-amino 4, 3-methoxy 5 and 3-hydrazino 8 derivatives. Oxidative dehydrazination of 8 with mercury(II) oxide (HgO) in ethanol gave 6-amino-5-benzylamino-1, 2, 4-triazine 1-oxide 9 in a moderate yield. The 1, 2, 4-triazine 1-oxides were then cyclized with triethyl orthoformate (TEOF) to afford the title compounds in 28–88% yields.