1. Institute of Organic Chemistry, University of Vienna, Währinger Straße 38, A-1090 Vienna, Austria
2. Department of Chemistry, State University of New York at Binghamton, Vestal
Parkway East, Binghamton, New York, New York 13902-6000, United States
3. Institute of Organic Chemistry, Justus-Liebig University, Heinrich-Buff-Ring 58, D-35392
Giessen, Germany