1. Department of Organic and Molecular Inorganic Chemistry, Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, Kiadis B.V., Zernikepark 6-8, 9747 AN Groningen, The Netherlands, DSM Pharma Chemicals, Advanced Synthesis, Catalysis and Development, P.O. Box 18, 6160 MD Geleen, The Netherlands, and Unilever R&D Vlaardingen, P.O. Box 114, 3130 AC Vlaardingen, The Netherlands