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DOI: 10.1055/s-2006-941997
Co-Catalyzed Radical Alkenylation of Alkyl Halides
Contributor(s):Paul Knochel, Andrei GavryushinKyoto University and Hiroshima University, Japan
Cobalt-catalyzed Trimethylsilylmethylmagnesium-Promoted Radical Alkenylation of Alkyl Halides: A Complement to the Heck Reaction
J. Am. Chem. Soc. 2006, 128: 8068-8077
Publication History
Publication Date:
21 July 2006 (online)
Key words
Heck reaction - cobalt catalysis - radical addition
Significance
This work describes a novel method of intermolecular coupling of alkenes with alkyl halides in the presence of trimethylsilylmethylmagnesium chloride and a cobalt catalyst CoCl2-1,6-bis(diphenylphosphino)hexane. In many cases it is an alternative to the Heck reaction because it does not require expensive palladium catalysts. This method shows good functional-group compatibility. The reaction proceeds via a radical pathway. An intramolecular version of this process allows to create complex carbon frameworks. Additionally, a Co-catalyzed cross-coupling of iodoalkenes with Me3SiCH2MgCl leading to allyltrimethylsilanes is described.
Comment
This original method is especially convenient for the synthesis of polysubstituted styrenes, including those bearing functional groups. Mechanistically, the key steps of the process are the formation of a radical from the alkyl halide, its addition to the double bond and the trapping of the product by the Co(l) complex. Since the process is of radical nature, either a styrene has to be used to ensure the selective radical attack, or the reaction has to be performed intramolecularly, affording cyclization products. Interestingly, trimethylsilylmethyl magnesium halide is a unique Grignard reagent, allowing to perform such transformations. The reaction has obviously a high synthetic potential.