1. Institut für Organische Chemie, Universität Hannover, Schneiderberg 1B, D-30167 Hannover, Germany, Centre of Molecular and Macromolecular Studies, Department of Organic Sulfur Compounds, Polish Academy of Sciences, PL-90-363 Łódź, Sienkiewicza 112, Poland, Department of Organic Chemistry, Maria Curie-Sklodowska University, Lublin, Poland, and Institute of Organic Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, PL-01-224 Warsaw, Poland