1. Faculty of Science, Department of Chemistry, Ataturk University, 25240 Erzurum, Turkey, Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany and Department of Chemistry, FB-110, University of Puerto Rico, RIO PIEDRAS, Puerto Rico 00931, and DSM Pharma Products, Innovative Synthesis and Catalysis, and Development, P.O. Box 18, 6160 MD Geleen, The Netherlands