A different type of MnO2-induced oxidative cyclization of dihydrotriazines has been developed. These dihydrotriazines are considered as a "formal" Schiff's base. This method provided easy access to naphthofuro-fused triazine via the C-C/C-O oxidative coupling reaction. The reaction sequence comprised the nucleophilic addition of 2-naphthol or phenol to 1,2,4-triazine, followed by oxidative cyclization. The scope and limitations of this novel coupling reaction have been investigated. Further application of the synthesized compound has been demonstrated by synthesizing carbazole-substituted benzofuro-fused triazines. The scalability of the reaction was demonstrated at a 40 mmol load. The mechanistic study strongly suggests that this reaction proceeds through the formation of an O-coordinated manganese complex.
Keywords: 1,2,4-triazine; cross-coupling; manganese(IV) oxide; oxidative cyclization; phenols.