1. Institute of Organic Chemistry, Russian Academy of Sciences, 630090 Novosibirsk, Russia, Fax: (internat.) + 7‐3832/344‐752
2. Department of Chemistry, University of Antwerp (UIA), Universiteitsplein 1, 2610 Wilrijk (Antwerpen), Belgium, Fax: (internat.) + 32‐3/820‐2310