1. Laboratory for Organic Synthesis, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001 Heverlee, Belgium, and Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstrasse 28, A-8010 Graz, Austria %erik.vandereycken@chem.kuleuven.ac.be; oliver.kappe@uni-graz.at