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; and Department of Organic Chemistry & Department of Molecular Spectroscopy, NSR Center, University of Nijmegen, 1 Toernooiveld, NL-6525 ED Nijmegen, The Netherlands