Biomimetic Epoxidation of Olefins Catalyzed by Metalloporphyrins with Molecular Oxygen

The direct oxidation of hydrocarbon is a field of both academic and industrial importance and challenge.[1-3] Catalytic oxidation is a key technology for converting petroleum-based feedstock to useful chemicals of a high oxidation state such as alcohols, carbonyl compounds, and epoxides. Millions of tons of these compounds are annually produced worldwide and find applications in all areas of chemical industries.[4-6] Epoxidation of olefins is an important reaction in organic synthesis because the formed epoxides are intermediates that can be converted to a variety of products.[7-10] Access to a variety of epoxides has largely been successful due to the remarkable catalytic activity of transition metal complexes, which have a unique ability to bring the alkene substrate and the oxygen source within the coordination sphere of the metal leaving to a facial transfer of oxygen atom to the carbon-carbon double bond.[11-15] Cytochrome P-450 enzymes are heme-containing monooxygenases and play a key role in the oxidative transformation of endogeneous and exogeneous molecules.[16-20] They are virtually ubiquitous in nature and are present in all forms of life like plants and mammals, as well as in some prokaryotic organisms such as bacteria.[21-23] The active site of P-450s contains a highly conserved prosthetic heme IX complex coordinated by a thiolate ligand from a cysteine residue (Figure 1). The primary function of cytochrome P-450 enzymes is the oxygenation of a wide variety of organic substrates by inserting one oxygen atom from O2 to the substrate and reducing the other oxygen atom with reducing equivalents to a water molecule, utilizing two electrons that are provided by NAD(P)H via a reductase protein (Scheme 1).