1. Contribution from the Department of Organic Chemistry, Eötvös Loránd University, Budapest, H-1117, Hungary, Department of Organic Chemistry, Technical and Economical University of Budapest, Budapest, H-1111, Hungary, Department of Chemistry, University of Toronto, Toronto, Ontario, Canada, M5S 3H6, and Department of Chemistry and Chemical Informatics, Faculty of Education, University of Szeged, Szeged, H-6725, Hungary