Direct (het)arylation of [1,2,4]triazolo[1,5-a]pyrimidines: Both eliminative and oxidative pathways

(Hetero)arylation of [1,2,4]triazolo[1,5-a]pyrimidine through the direct nucleophilic CH functionalization of the C-7 and C-5 positions has been implemented. The regioselective addition of a (het)aryl magnesium bromide to C-7 of 6-bromo-[1,2,4]triazolo[1,5-a]pyrimidine, followed by eliminative aromatization of the intermediate σH-adducts, has afforded 7-(hetero)aryl-substituted [1,2,4]triazolo[1,5-a]pyrimidines (the SNH reaction, proceeding according to the “addition-elimination” scheme). A second treatment with a Grignard reagent has resulted in the C-5 σH-adducts, which have been oxidized while being N-magnesium salts into [1,2,4]triazolo[1,5-a]pyrimidines, bearing various combinations of (hetero)aromatic substituents at C-5 and C-7 (the SNH process, realizing via the “addition-oxidation” scheme). As a result of optical and electrochemical studies, the obtained compounds have proved to be promising luminescent dyes and push-pull systems.

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