1. Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, Advanced Synthesis, Catalysis and Development, DSM Pharma Products, PO Box 18, 6160 MD Geleen, The Netherlands, and Unilever R&D Vlaardingen, PO Box 114, 3130 AC Vlaardingen, The Netherlands