6.12 - Asymmetric Epoxidation and Sulfoxidation

Abstract

Both epoxides and sulfoxides are important families of compounds, many of which are biologically active or have been applied in the synthesis of biologically active compounds. In many cases, in order to exert its biological activity, there is a requirement that the molecule be optically pure with a defined absolute configuration. Catalytic asymmetric epoxidation of olefins, and catalytic oxidation of sulfides with metal based catalysts are the current methods of choice to access such compounds in these states. This chapter focuses on these methods, in the homogenous phase. Key applications of these methods, particularly in the industrial context, are mentioned. The chapter is written in a systematic fashion, commencing with the epoxidation methods, and being divided up according to the principle metal involved. For both reaction processes, first the more well known catalytic procedures, with more common metal based catalysts (e.g., Titanium, Manganese, Vanadium, and Molybdenum etc) are considered, terminating with applications of less common or novel catalysts (like, those based on alkaline earth oxides, and lanthanoid based systems). The advantage of this method of categorization is that in the context of catalytic epoxidation it leads to a clean division between electrophilic and nucleophilic processes. Both the efficiency and selectivity of the oxidation event are discussed, in terms (generally) of reaction yield and enantioselectivity, as well as a careful discussion of the catalyst structure, synthesis and stability, not to mention a thorough review of the reaction mechanism and/or of the catalytic cycle. In many cases throughout this chapter these aspects are compared between different catalytic systems, highlighting the advantages and disadvantages of each method. Where appropriate, for aspects outside the remit of this chapter, the reader is referred to the most appropriate literature available.