An efficient route to polynitrogen-fused tricycles via a nitrene-mediated N–N bond formation under microwave irradiation

The synthesis of unprecedented fused azaheterocyclic ring systems is described. Tricycles with either a central pyrazole or a triazole ring were obtained via a nitrene-mediated reaction of nitro bis(hetaryl) derivatives in the presence of triethylphosphite. The cyclization proceeded with complete chemoselectivity for the desired N–N bond formation and was completed within minutes under microwave activation. The key nitro bicycles were synthesized using either Stille couplings or aromatic nucleophilic substitution.