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, bioiso steric isomers of antiviral 9-benzylpurines, have been prepared. Oxida tion of mino-5-benzylamino-3-methylsulfanyl-1,2,4-triazine 1 with exce ss of m-chloroperbenzoic acid afforded mino-5-benzylamino-3-methylsulf onyl-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 nucleo philes to give 3-amino 4, 3-methoxy 5 and 3-hydrazino 8 derivatives. O xidative 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 yiel d. The 1,2,4-triazine 1-oxides were then cyclized with triethyl orthof ormate (TEOF) to afford the title compounds in 28-88% yields.