1. Department of Chemistry University of Oxford Chemistry Research Laboratory 12 Mansfield Road Oxford OX1 3TA United Kingdom
2. Georg-August-Universität Institute of Organic and Biomolecular Chemistry Tammannstr. 2 37077 Göttingen Germany
3. UCSD/CNRS Joint Research Chemistry Laboratory Department of Chemistry University of California San Diego La Jolla CA 92521-0403 USA