Affiliation: | 1. Department of Organic Chemistry, University of Geneva, 30 Quai E. Ansermet, 1211 Geneva 4 (Switzerland), Fax: (+41)?22‐379‐32‐15;2. Université de Nantes, CNRS, CEISAM UMR 6230, B.P. 92208, 2 rue de la Houssinière, 44322 Nantes Cedex 03 (France) |