1. Department of Chemistry, University of Warsaw, Pasteura 1, PL‐02‐093 Warsaw;2. Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, PL‐01‐224 Warsaw, (phone: +41?22?780?36?10;3. fax:+41?22?780?33?34;4. phone: +48?22?632?05?78;5. fax: +48?22?632?66?81);6. Present address: Firmenich SA, Corporate R&D Division, P.O. Box 239, CH‐1211 Geneva 8.