Selective oxidation catalysis with Mn and H2O2: Conversion of alkenes to α-hydroxy ketones, C=C cleavage and mechanistic insights.

Oxidation is a term used to cover a wide range of processes that are central to life. Although we associate oxidation with ageing it is in fact central to living – from the uncontrolled radical chain reactions that drive combustion to the highly selective stepwise oxidations that your body uses to breakdown food (sugars and fats) to the bodies energy currencies, ATP, NADH etc., carbon dioxide and water. The selective stepwise oxidation of organic substrates is the central theme of this thesis in which a remarkably simple, in terms of usage and application, catalyst system is used together with hydrogen peroxide. The challenge is to carry out multistep oxidation of important organic building blocks to yield useful synthons for a wide range of fine chemical use. Critically, the catalyst system is based on an environmentally benign oxidant, hydrogen peroxide, which produces only water as a by-product, and a first row transition metal, manganese, which is readily available and non-toxic. The efficiency of the catalyst system furthermore is remarkable with turnover frequencies of over 30 s-1 and turn over numbers in excess of 300000 in some cases.
The thesis examines several aspects of the chemistry of this system, beginning with selectivity – can we oxidize one compound selectively in the presence of another. The use of the catalyst system in multistep oxidations where the product of the first step becomes the starting material for the next is explored in depth and we show that we can provide a viable alternative to the hazardous use of ozone in organic synthesis. Finally we show that post-polymerization modification of rubbers is possible with this system using unusual solvent combinations, which opens up tremendous opportunities in expanding the scope of properties of these ubiquitous materials.