1. Laboratory of Molecular Catalysis, Laboratory of New Organic Materials, and Laboratory of Theoretical Chemistry, Institute of ChemistryUFRGS Av. Bento Gonçalves, 9500 Porto Alegre 91501-970 RS Brazil, Instituto de Química, Universidade de São Paulo, Caixa Postal 26.077, São Paulo 05599-970, Brazil, and Organisch-Chemisches Institut der Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany