SNH reactions of 1,2,4-triazine N-oxides, pyrazine N-oxides, and pterin N-oxides with arenethiols*

1,2,4-Triazine 4-oxides were found to enter into the reactions of nucleophilic substitution of hydrogen with S-nucleophiles (arenethiols) in the presence of acylating agents and trifluoroacetic acid. The reactions proceeded with loss of the N-oxide function to form 5-arylthio-1,2,4-triazines. 2-Amino-3-ethoxycarbonylpyrazine 1-oxides and 2-amino-4-oxopterin 8-oxides react with arenethiol analogously.