A New Class of Pyrazolopyridine Nucleus with Fluorescent Properties, Obtained through Either a Radical or a Pd Arylation Pathway from N-Azinylpyridinium N-Aminides Valentina Abet, † Araceli Nun ˜ez, † Francisco Mendicuti, ‡ Carolina Burgos,* ,† and Julio Alvarez-Builla* ,† Departamentos de Quı ´mica Orga ´nica and Quı ´mica Fı ´sica, UniVersidad de Alcala ´, 28871 Alcala ´ de Henares, Madrid, Spain carolina.burgos@uah.es; julio.alVarez@uah.es ReceiVed July 17, 2008 The synthesis of dipyridopyrazole and pyridopyrazolopyrazine derivativessboth of which incorporate a 3-aryl moietyscan be achieved in moderate yields by intramolecular radical arylation of pyridinium N-aminides using tris(trimethylsilyl)silane and azobisisobutyronitrile. Improved results were obtained on using Pd direct arylation in conjunction with microwave irradiation. A preliminary study into the fluorescent properties of the target compounds is also reported. Introduction Azaindolizines (e.g., II-IV, Figure 1) with additional nitro- gens in either the azine ring (II) or the azole ring (III) or both (IV) are rare systems in nature, and their similarity to both indoles and purines has triggered recent interest in their study. Some remarkable members of these families are the biologically relevant variolins 1 and luciferins, 2 which are related to classes II and IV, respectively (Figure 1). Examples of type III systems include the antiallergic and cerebroactive agent ibudilast and the highly selective D 4 receptor partial agonist FAUC 113 (Figure 2), which have been prepared for assessment of their pharmacological activity. 3 † Departamento de Quı ´mica Orga ´nica. ‡ Departamento de Quı ´mica Fı ´sica. (1) (a) Anderson, R. J.; Hill, J. B.; Morris, J. C. J. Org. Chem. 2005, 70, 6204–6212. (b) Karpov, A. S.; Merkul, E.; Rominger, F.; Muller, T. J. J. Angew. Chem., Int. Ed. 2005, 44, 6951–6956. (c) Perry, N. B.; Ettouati, L.; Litaudon, M.; Blunt, J. W.; Munro, M. H. G.; Parkin, S.; Hope, H. Tetrahedron 1994, 50, 3987–3992. (d) Trimurtulu, G.; Faulkner, D. J.; Perry, N. B.; Ettouati, L.; Litaudon, M.; Blunt, J. W.; Munro, M. H. G.; Jameson, G. B. Tetrahedron 1994, 50, 3993–4000. (2) (a) Zhou, W.; Shultz, J. W.; Murphy, N.; Hawkins, E. M.; Bernad, L.; Good, T.; Moothart, L.; Frackman, S.; Klaubert, D. H.; Bulleit, R. F.; Wood, K. V. Chem. Commun. 2006, 4620–4622. (b) Travert, N.; Al-Mourabit, A. J. Am. Chem. Soc. 2004, 126, 10252–10253. (c) Topalov, G.; Kishi, Y. Angew. Chem., Int. Ed. 2001, 40, 3892–3894. FIGURE 1. General structure of indolizine and azaindolizines and some related natural products. 10.1021/jo801549u CCC: $40.75  2008 American Chemical Society 8800 J. Org. Chem. 2008, 73, 8800–8807 Published on Web 10/21/2008