Iron–Copper Cooperative Catalysis in the Reactions of Alkyl Grignard Reagents: Exchange Reaction with Alkenes and Carbometalation of Alkynes

Abstract

Iron-copper cooperative catalysis is shown to be effective for an alkene-Grignard exchange reaction and alkylmagnesiation of alkynes. The Grignard exchange between terminal alkenes (RCH═CH(2)) and cyclopentylmagnesium bromide was catalyzed by FeCl(3) (2.5 mol %) and CuBr (5 mol %) in combination with PBu(3) (10 mol %) to give RCH(2)CH(2)MgBr in high yields. 1-Alkyl Grignard reagents add to alkynes in the presence of a catalyst system consisting of Fe(acac)(3), CuBr, PBu(3), and N,N,N',N'-tetramethylethylenediamine to give β-alkylvinyl Grignard reagents. The exchange reaction and carbometalation take place on iron, whereas copper assists with the exchange of organic groups between organoiron and organomagnesium species through transmetalation with these species. Sequential reactions consisting of the alkene-Grignard exchange and the alkylmagnesiation of alkynes were successfully conducted by adding an alkyne to a mixture of the first reaction. Isomerization of Grignard reagents from 2-alkyl to 1-alkyl catalyzed by Fe-Cu also is applicable as the first 1-alkyl Grignard formation step.

Iron‐Catalysed Hydrofunctionalisation of Alkenes and Alkynes

“…[154] It was suggested that the alkene by-product produced during the reaction might act as a stabilising ligand on iron. In contrast to previous reports by Shirakawa and Hayashi [147] and Ready [155] on the iron-catalysed addition of alkyl Grignard reagents to di-substituted alkynes and (homo)propargylic alcohols, respectively, no products arising from carbomagnesiation were reported by Nakamura. It was unclear why 2 equivalents of ethylmagnesium bromide were required, as unreacted ethylmagnesium bromide remained at the end of reaction; however, lower equivalents of ethylmagnesium bromide led to inferior yields of hydromagnesiation products.…”

“…[147] A combination of FeCl 3 (2.5 mol %), CuBr (5 mol %) and tributylphosphine (10 mol %) was found to be effective for the hydromagnesiation of terminal aliphatic alkenes by using cyclopentylmagnesium bromide (281) as the stoichiometric hydride source (Scheme 62 A). As internal alkenes were found to be unreactive under the reaction conditions, the formation of cyclopentene (282) following "HÀMgX" transfer from cyclopentylmagnesium bromide (281) effectively removed this alkene by-product from the reaction and led to the formation of hydrofunctionalised products 283 in generally high yields.…”

Enantioselective Incorporation of CO2: Status and Potential

“…Several alkene hydrocarboxylations have been reported, including some that provide chiral molecules, however, all but one yield racemic mixtures. 12,13,14,16,49,103 A particular challenge is the need for additives that promote catalyst regeneration and product release. 12,13,14,49 These additives may interfere with the ability to make reactions enantioselective: for example, known iron-based hydrocarboxylation catalysts depend on Grignard reagents, 13 109,111,112 The regioselectivity may differ from the example shown here.…”

Ni- and Fe-catalyzed Carboxylation of Unsaturated Hydrocarbons with CO2

“…The involvement of nickel hydride species was slightly more favorable energetically, with a significantly lower energetic difference for electron-rich substrates, an observation that could explain their lack of reactivity. As for the nickel hydride Prompted by the seminal work of Rovis on the Ni-carboxylation of styrenes [76] as well as by the work of Hayashi and Shirakawa on the Fe-and Cu-catalyzed hydromagnesiation of terminal alkenes [78], Thomas reported the preparation of α-methyl arylacetic acids in the presence of cheap and bench-stable iron/bis(imino)pyridine catalyst and Grignard reagents at room temperature (Scheme 21).…”