6‐ and 7‐aryl‐1,2,4‐triazolo[4,3‐ b ]‐1,2,4‐triazines. Synthesis and characterization

Synthetic methods for the preparation of 6‐aryl‐1,2,4‐triazolo[4,3‐ b ]‐1,2,4‐triazines ( 1 ) and the 7‐aryl isomers ( 2 ) are described. Compounds 1 were prepared from aryl glyoxaldoximes 76 via 6‐aryl‐1,2,4‐triazin‐3(2 H )ones ( 75 ). A simple procedure for the preparation of the 7‐aryl isomers was effected using arylglyoxals 11 and the triazoles ( 4, 12a and 12b ). However, complete regioselectivity was not realized in all cases, especially when the triazoles were substituted at the C‐5 position. A regiospecific synthesis of the 7‐aryl isomers 2 was developed via the 3‐methylthio‐5‐aryl‐1,2,4‐triazines ( 61 ). The structure of the parent 6‐phenyl derivative 5 was confirmed by x‐ray crystallography.