1,2,4‐Triazines. 5 . Regioselective N2‐amination of 3‐methylthio‐1,2,4‐triazin‐5(2 H )‐ones. A new efficient synthesis of [1,2,4]triazolo[2,3‐ b ][1,2,4]triazin‐7(1 H )‐one

A regioselective synthesis of 2‐amino‐1,2,4‐triazinones ( 3a‐b ) is reported, by reaction of 3‐methylthio‐1,2,4‐triazinones ( 1a‐b ) with O ‐(2,4‐dinitrophenyl)hydroxylamine ( 2 ), as an amino transfer agent. A spectroscopic study and an unequivocal synthesis of 2‐amino‐4‐methyl‐6‐phenyl‐1,2,4‐triazinone ( 8a ) has shown the site of amination to be N2 of the 1,2,4,‐triazinone ring. Subsequent reaction of 2‐amino‐1,2,4‐triazinone ( 3b ) with ammonium hydroxide, followed by ring closure with formic acid provided [1,2,4]triazolo[2,3‐ b ][1,2,4]triazin‐7 (1 H )‐one ( 10 ).