Oxygenation of Styrene by Cytochrome P-450 Model Systems: A Mechanistic Study

Article abstract of DOI:10.1021/ja00270a016

The manganese and iron porphyrin catalyzed oxygenation of styrene results in the production of phenylacetaldehyde as well as the expected epoxide.It is demonstrated that aldehyde is a primary product and dose not result from isomerization of styrene oxide.Isotope labeling studies show that one of the β hydrogen atoms of styrene migrates to the benzylic carbon in the course of aldehyde formation.Experiments using cis and trans deuterated styrenes reveal that there is a stereoelectronic preference for migration of the hydrogen cis to the aromatic ring.Styrene, styrene-d8, and cis-β-deuteriostyrene yield similar ratios of epoxide to aldehyde, indicating that β hydrogen migration occurs after the rate-determining step for formation of phenylacetaldehyde.The mechanism of this rearrangement is discussed.Some new information concerning the mechanism of olefin epoxidation by these catalysts is also presented.These results may have relevance to the mechanism of alkene oxygenation by the cytochrome P-450 monooxygenase enzymes.