1. Institute of Organic Chemistry, NW2 C, University of Bremen, 28334 Bremen, Germany
2. Institute for Inorganic and Physical Chemistry, NW2 C, University of Bremen, 28334 Bremen, Germany, Fax: (internat.) + 49‐421‐218‐4267
3. Institute of Organic Chemistry, Russian Academy of Sciences, 630090 Novosibirsk, Russia, Fax: (internat.) + 7‐3832‐344‐752