1. Institut für Organische Chemie der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany, Department of Chemistry, Facundo Bueso 110, University of Puerto Rico, Rio Piedras, Puerto Rico 00931, and Institute of Organic Chemistry, Ufa Scientific Center of the RAS, 71 Prospect Oktyabrya, 450054 Ufa, Russia