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. (C) 2008 Published by Elsevier Ltd.