Cobalt-Catalyzed Trimethylsilylmethylmagnesium-Promoted Radical Alkenylation of Alkyl Halides: A Complement to the Heck Reaction
Citations Over TimeTop 10% of 2006 papers
Abstract
A cobalt complex, [CoCl2(dpph)] (DPPH = [1,6-bis(diphenylphosphino)hexane]), catalyzes an intermolecular styrylation reaction of alkyl halides in the presence of Me3SiCH2MgCl in ether to yield beta-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can participate in the styrylation. A radical mechanism is strongly suggested for the styrylation reaction. The sequential isomerization/styrylation reactions of cyclopropylmethyl bromide and 6-bromo-1-hexene provide evidence of the radical mechanism. Crystallographic and spectroscopic investigations on cobalt complexes reveal that the reaction would begin with single electron transfer from an electron-rich (diphosphine)bis(trimethylsilylmethyl)cobalt(II) complex followed by reductive elimination to yield 1,2-bis(trimethylsilyl)ethane and a (diphosphine)cobalt(I) complex. The combination of [CoCl2(dppb)] (DPPB = [1,4-bis(diphenylphosphino)butane]) catalyst and Me3SiCH2MgCl induces intramolecular Heck-type cyclization reactions of 6-halo-1-hexenes via a radical process. On the other hand, the intramolecular cyclization of the prenyl ether of 2-iodophenol would proceed in a fashion similar to the conventional palladium-catalyzed transformation. The nonradical oxidative addition of carbon(sp2)-halogen bonds to cobalt is separately verified by a cobalt-catalyzed cross-coupling reaction of alkenyl halides with Me3SiCH2MgCl with retention of configuration of the starting vinyl halides. The cobalt-catalyzed intermolecular radical styrylation reaction of alkyl halides is applied to stereoselective variants. Styrylations of 1-alkoxy-2-bromocyclopentane derivatives provide trans-1-alkoxy-2-styrylcyclopentane skeletons, one of which is optically pure.
Related Papers
- → Metallic Palladium in the Heck Reaction: Active Catalyst or Convenient Precursor?(2001)197 cited
- → Reactions of 9-Triptyceneselenol with Palladium(0) Complexes: Unexpected Formations of the Dinuclear Palladium(I) Complex [{Pd(PPh3)}2(μ-SeTrip)2] and Five-Membered Selenapalladacycle [Pd(η2(C,Se)-Trip)(dppe)](2009)32 cited
- → Preparation, Structure, and Reactions of Trifluoroacetimidoyl Palladium(II) Complexes(2011)17 cited
- → Selectivity in reductive elimination from dialkyl(aryl)palladium(IV) complexes, and the observation of benzyl halide transfer from palladium(IV) to palladium(II). The X‐ray structure of methyl(phenyl)(2,2′‐bipyridyl)palladium(II)(1991)24 cited
- → Metallic Palladium in the Heck Reaction: Active Catalyst or Convenient Precursor?(2001)2 cited