1. Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
2. X-ray Crystallography Laboratory, Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
3. Institut für Organische Chemie, Friedrich-Alexander-Universität, Erlangen-Nürnberg, Henkestrasse 42, D-91054 Erlangen, Germany