Organic Chemistry is mainly dealing with the synthesis of molecules. In order to be able to do this efficiently, one must have reasonable insight into the way in which bonds between atoms can be formed or broken and how molecules can react with each other. In our research proposal we make use of the special properties of an interesting class of molecules containing selenium atoms. The properties of these selenium-containing molecules are wide spread and we propose to investigate their use in different areas. In this proposal we describe the development of reactions using only catalytic amounts of these reagents. This means that one catalyst molecule will have the potential to create thousands of new molecules with special properties. The development of these new selenium reagents and their application in a certain type of reactions, the electrophilic addition reaction to carbon-carbon double bonds and oxygen-transfer reactions, form the main part of this proposal. The development of reaction sequences with these reagents as catalysts will be studied in much more detail and further optimisation of the selenium reagents are necessary for an efficient performance in the catalytic reactions. The use of 'green', peptide-based catalysts is a novel and special feature for selenium reagents. Applications of these methodologies to the synthesis of target structures are further points of interest and will be focussed upon towards the end of the project.