Nucleophilic substitution of hydrogen in pyrazine N-oxides under the action of CH-active compounds requires activation with acylating agents. This activation facilitates aromatization of intermediate sigma(H) adducts via elimination of the acid residue to form substituted pyrazines. More electrophilic 1,2.4-triazine 4-oxides react with carbanions derived from CH-active compounds without additional activation according to a scheme, which has previously been unknown for azine N-oxides. This scheme involves aromatization of a H adducts through elimination of water by the E1cb mechanism. The reaction products occur in DMSO-d(6) Solutions predominantly as 6-methylene-1,6-dihydropyrazines and 5-methylene-4,5-dihydro-1,2,4-triazines.
The scope of functionalization of 1,2,4-triazines can be considerably extended via successive nucleophilic substitution of hydrogen (S-N(H)) and ipso-substitution. A convenient procedure has been developed for direct cyanation of 1,2,4-triazine 4-oxides with acetone cyanohydrin in the presence of triethylamine. The cyano group in the resulting 5-cyano-1,2,4-triazines is readily replaced by reactions with various aliphatic alcohols and amines.