Pentanidium-Catalysed a-Hydroxylation Reactions of Cyclic Ketones

Abstract

Phase transfer catalysis has developed tremendously since it was first introduced by Starks in 1971. Many variants of the catalysts have been developed by research groups to facilitate a myriad of reactions. Recently, the development of chiral phase transfer catalysts has made this branch of catalysis even more promising. Our group has recently developed the pentanidium catalyst, a chiral phase transfer catalyst. It is an attractive catalyst as it can be synthesised easily with large scale of up to 500 mg, it has an easily modifiable structure and it has the ability to catalyse a range of reactions. In this thesis, enantioselective alpha-hydroxylation reactions were successfully carried out using the pentanidium catalyst using only molecular oxygen as the oxidant. Relatively decent enantioselectivities of between 60 to 90 % and moderate yields of 40 % were achieved. A study of the mechanism of the reaction reveals that the reaction proceeds through a 2 step pathway involving the formation of a hydroperoxy intermediate which reactions with another molecule of oxygen to yield the desired product.