Synthesis of triazolo[1,5-a]triazin-7-one derivatives and highly functionalized [1,2,4]triazoles

Abstract

The synthesis of novel triazolo[1,5-a]triazin-7-ones is presented. Starting from 3-amino-5-sulfanyl-1,2,4-triazole, the synthetic sequence involved alkylation with benzyl bromide, reaction with p-nitrophenyl chloroformate followed by treatment with a primary amine, and condensation with diethoxymethyl acetate. Final oxidation of the thioether moiety with 3-chloroperbenzoic acid provided 2-(benzylsulfonyl)[1,2,4]tri-azolo[1,5-a][1,3,5]triazin-7-ones 5a and 5b in good overall yields. Treatment of 5a and 5b with secondary amines provided highly functionalized [1,2,4]triazoles through an unexpected triazinone ring opening. A mechanism for this transformation is proposed.