1 Departamento de Quimica Organica, Universidad de Cordoba, Campus de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396, 14014 Cordoba (Spain), Fax: (+34) 957212066. q62alsor@uco.es.
2 Department of Chemistry, Western Michigan University, 1903 W. Michigan Avenue, Kalamazoo, MI 49008-5413 (USA), Fax: (+1) 269-387-2909. sherine.obare@wmich.edu.