Selectivity in Palladium- and Enzyme-Catalyzed Reactions : Focusing on Enhancement of Reactivity

Sammanfattning: Catalysis has a profound impact on all living species on the earth. Nature’s catalysts, the enzymes, have the ability to selectively promote a specific bio-chemical transformation, given the required substrate. As well as being highly selective, enzymes enhance the speed of these reactions, helping them to run at temperatures much lower than normally required, i.e. at body temperature. In comparison, reactions used in the production of new materials such as polymers, medicines, fragrances, petrochemicals, etc. are often catalyzed by transition metals. This thesis describes how the selectivity and activity of these catalysts can be influenced via two conceptually different methods: chelation control and microwave heating. The thesis primarily focuses on regio- and stereochemical aspects of the palladium-catalyzed arylation of olefins, i.e. the Heck reaction. Reaction rate enhancement of both palladium and enzyme (polymerase chain reaction [PCR]) catalysis by microwave heating is also discussed. Novel chelation-controlled palladium-catalyzed multi- and asymmetric arylations of vinyl ethers were performed, resulting in tetra-substituted olefins as well as chiral quaternary carbon centers with excellent optical purity. In addition, a new synthetic route to diarylated ethanals, relying on a double chelation-controlled regioselective arylation followed by hydrolysis, has been discovered. High temperature conditions, using microwave heating, substantially reduce the reaction time for ligand-controlled asymmetric Heck arylations, while retaining levels of enantioselectivity in most cases. In addition, a potentially useful fast synthetic protocol for the employment of aryl boronic acids in oxidative Heck arylation was developed. Finally, microwave-assisted PCR was described for the first time; this method allows reductions in the run time of 50%.