Molecular oxygen and hydrogen peroxide as mild oxidants in catalytic oxidations : Applications to palladium and osmium catalysis

Sammanfattning: In this thesis the use of molecular oxygen and hydrogen peroxide as mild oxidants in transition metal-catalyzed oxidations of organic substrates is discussed. The thesis is divided into three parts.In the first part the use of heteropolyacids as robust oxygen-activating agents for aerobic reoxidation of zerovalent palladium is described. This aerobic reoxidation system has been applied to two different palladium-catalyzed reactions, the allylic oxidation of cyclohexene and the 1,4-oxidation of conjugated dienes. It was demonstrated that the presence of a benzoquinone, which can act both as an electron-transfer mediator and a coordinating ligand in the intermediate palladium π-allyl complex, is of importance for efficient reactions.In the second part, studies of systems for mild oxidations of tertiary amines to amine N-oxides are described. It was found that a fully reduced N1,N5- dialkylblocked flavin catalyzes the H2O2 oxidation of tertiary amines, giving the amine N-oxides in good yields in fast reactions. The reduced flavin acts as a precursor of the active catalyst, which is generated in the presence of air. Co(salophen), another investigated potential catalyst, was found to form a 1:2 complex with N-methylmorpholine N-oxide (NMO). This catalyst-product complex may inhibit the amine oxidations.The final part deals with in situ generation of NMO from N-methylmotpholine (NMM) in the osmium-catalyzed dihydroxylation of olefins. In a model study it was demonstrated that mCPBA in the presence of catalytic amounts of NMM is an efficient reoxidant for osmium(VI) in the dihydroxylation. Further investigations showed that H2O2 is an excellent oxidant in osmium-catalyzed dihydroxylations where NMM and a flavin are employed as cocatalysts. Different cis diols were synthesized in good yields by this procedure.