Selective iron-catalyzed cross-coupling reactions of grignard reagents with enol triflates, acid chlorides, and dichloroarenes.

Bodo Scheiper, Melanie Bonnekessel, Helga Krause, Alois Fürstner

Index: J. Org. Chem. 69 , 3943-3949, (2004)

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Abstract

Cheap, readily available, air stable, nontoxic, and environmentally benign iron salts such as Fe(acac)(3) are excellent precatalysts for the cross-coupling of Grignard reagents with alkenyl triflates and acid chlorides. Moreover, it is shown that dichloroarene and -heteroarene derivatives as the substrates can be selectively monoalkylated by this method. All cross-coupling reactions proceed very rapidly under notably mild conditions and turned out to be compatible with a variety of functional groups in both reaction partners. A detailed analysis of the preparative results suggests that iron-catalyzed C-C bond formations can occur via different pathways. Thus, it is likely that reactions of methylmagnesium halides involve iron-ate complexes as the active components, whereas reactions of Grignard reagents with two or more carbon atoms are effected by highly reduced iron-clusters of the formal composition [Fe(MgX)(2)](n) generated in situ. Control experiments using the ate-complex [Me(4)Fe]Li(2) corroborate this interpretation.