1. Departamento de Química Orgánica (C-I), Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain, Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, Department of Chemistry, University of Miami, Coral Gables, Florida 33124, and Department of Chemistry, Pontifical Catholic University, Ponce, Puerto Rico 00732