1. Department of Chemistry, University of Bergen, Allégt 41, NO-5007 Bergen, Norway, Department of Organic Chemistry, National University of Mongolia, P.O. Box 46, Post Office 46, Ulaanbaatar 210646, Mongolia, and Fakultät für Chemie and Bioanorganische Chemie, Technische Universität Dortmund, Otto-Hahn-Strausse 6, DE-44227 Dortmund, Germany