Formation of C-O Bonds

Asymmetric allylic oxidation and benzylic oxidation (Kharasch-PSosnovsky reaction) are important synthetic strategies for constructing chiral C—O bonds via C—H bond activation.In the mid-1990s, the asymmetric Kharasch-Sosnovsky reaction was first studied by using chiral C2-symmetric bis(oxazoline)s. Later various chiral ligands, based mainly on oxazoline derivatives and proline derivatives, were used in such asymmetric oxidation. Although many efforts have been made to improve the enantioselective Kharasch-Sosnovsky oxidation reaction, most cases suffered from low to moderate enantioselectivities or low reactivities. 

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This observation opens up a new possibility in the formation of C - O bonds for the already comphcated oxygenation reactions of organic substrates, i.e., the non-innocent behavior of the olefin in open-shell transition metal olefin complexes can allow a direct radical couphng of dioxygen with the coordinated olefin. 

J. O. Metzger, Reactions of Radicals with Formation of C,O-Bond, in Methoden Org. Chem. (Houben-Weyl) 4th ed. 1952-, C-Radicals (M. Regitz, B. Giese, Eds.), Vol. E19a, 383, Georg Thieme Verlag, Stuttgart, 1989. 

A. Berkessel, Formation of C-O Bonds by Conjugate Addition of O-Nucleophiles , in Stereoselective Synthesis (Houben-Weyl) 4th ed. 1996, (G. Helmchen, R. W. Hoffinann, J. Mulzer, E. Schaumann, Eds.), 1996, Vol. E21 (Workbench Edition), 8, 4818—4856, Georg Thieme Verlag, Stuttgart. 

Woggon, W. D. Formation of C-O Bonds by Allylic Oxidation with Selenium(iv) Oxide. In Houben-Weyl Helmchen, G., Hoffmann, R. W., Mulzer, J., Schaumann, E., Eds. Thieme Stuttgart, 1996 Vol. E21, pp 4947-4956. 

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