Iron-Catalyzed Arylations of Alkyl Pseudo Halides

Iron-Catalyzed Arylations of Alkyl (Pseudo)Halides 

In sharp contrast to the palladium- and nickel-catalyzed cross-couplings described above, iron catalysts show a high catalytic activity towards secondary alkyl halides, as reported by Nakamura and coworkers. Thus, cyclohexyl chloride, bromide or iodide can be arylated by a phenyl Grignard reagent in almost quantitative yield in the presence of FeCh as catalyst, along with an excess amount of a diamine additive N,N,N, N -tetramethylethylenediamine (TMEDA). Primary alkyl halides, such as octyl chloride, bromide and iodide, can also be arylated by the action of the same iron catalyst. However, the yields are somehow decreased, especially when primary alkyl chlorides are used as electrophiles (Equations 5.24 and 5.25) [33]. 

Entry X M Nickel catalyst (or precatalyst) Solvent Examples Yield [%Y Reference 

Fiirstner reported that a low-valent iron(-II) complex catalyzed the crosscouplings of primary and secondary alkyl halides with various aryl Grignard reagents under such mild reaction conditions that chemoselective arylations would be feasible in the presence of potentially reactive functional groups, such as carbonyl, cyano and isocyanato groups. While aUcyl bromides and iodides showed excellent reactivities with this iron catalyst system, aUcyl chlorides were found to be inert under the reported reaction conditions (Equation 5.27) [35]. 

An iron-salen complex can also catalyze the arylation of alkyl halides with organomagnesium compounds. Bedford and coworkers reported that the crosscoupling of primary and secondary alkyl halides with aryl Grignard reagents takes place in the presence of the iron complex 15 to give the corresponding alkyl-substituted arenes in good yields (Equation 5.28) [36]. 

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Iron-Catalyzed Arylations of Alkyl (Pseudo) Halides j 169... 

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