New systems for catalytic asymmetric epoxidation

This thesis describes the catalytic asymmetric epoxidation of olefins mediated by oxaziridinium salts. The introduction highlights some of the most successful methods for preparing chiral oxiranes and hints at the synthetic utility of this versatile molecule. The final section of this chapter describes previous Page group findings. The second chapter is dedicated to our efforts to synthesize chiral iminium salts as catalysts for asymmetric epoxidation and leads on to the current authors efforts in this area. The aim of this project was to minimise rotation about the C–N bond of these iminium salt catalysts. The original catalyst architecture was based on an oxazolidine structure. Initial results showed that to form active oxazolidine based tetrahydroisoquinolinium catalysts a quaternary centre between the nitrogen and oxygen atoms must be present. Catalysts derived from ketones and (3S)-hydroxy methyl-1,2,3,4-tetrahydroisoquinoline were therefore sought. Several catalyst precursors were synthesized using microwave technology and converted to the corresponding iminium salts, unfortunately epoxidation of several unfunctionalized alkenes using Oxone as the stoichiometric oxidant resulted in near racemic epoxide. [Continues.]