1. Contribution from the Department of Organic Chemistry, Kiev Polytechnic Institute, pr. Pobedy 37, 252056 Kiev, Ukraine, Georg-August University Göttingen, Institute of Organic Chemistry, Tammannstr. 2, D-37077 Göttingen, Germany, and Technical University Braunschweig, Braunschweig, Institute of Organic Chemistry, Hagenring 30, D-38106, Germany