Carbometalation

Carbometalation (less often carbometallation) is an organometallic reaction involving the insertion of alkenes and alkynes into a metal-carbon bond. Organolithium compounds, organocopper compounds, and Grignard reagents characteristically participate, but the scope is large.[1] Carbometalation produces new organometallic compounds, which themselves are amenable to further modification.

The carbometalation of alkynes can yield the cis or trans isomer. With unsymmetrical alkynes the organometallic compound can add in two different way, thus control of regioselectivity is important.

Scope

Illustrative is the Fe-catalyzed reaction of methylphenylacetylene with phenylmagnesium bromide, which generates a vinyl magnesium intermediate. Hydrolysis affords the diphenylalkene:[2][3]

Another demonstration of this reaction type is an alternative route to tamoxifen starting from diphenylacetylene and ethyllithium:[4]

The capturing electrophile here is triisopropyl borate forming the boronic acid R–B(OH)2. The second step completing tamoxifen is a Suzuki reaction.

References

  1. ↑ Flynn, A. B.; Ogilvie, W. W. (2007). "Stereocontrolled Synthesis of Tetrasubstituted Olefins". Chem. Rev. 107: 4698–4745. doi:10.1021/cr050051k.
  2. ↑ Shirakawa, Eiji; Yamagami, Takafumi; Kimura, Takahiro; Yamaguchi, Shigeru; Hayashi, Tamio (2005). "Arylmagnesiation of Alkynes Catalyzed Cooperatively by Iron and Copper Complexes". J. Am. Chem. Soc. (Communication). 127 (49): 17164–17165. doi:10.1021/ja0542136.
  3. ↑ In this reaction the Grignard reagent combines with iron acetylacetonate and tributylphosphine to give an ill-defined aryliron intermediate, which then reacts with copper(I) chloride an intermediate cuprate.
  4. ↑ McKinley, Neola F.; O'Shea, Donal F. (2006). "Carbolithiation of Diphenylacetylene as a Stereoselective Route to (Z)-Tamoxifen and Related Tetrasubstituted Olefins". J. Org. Chem. (Note). 71 (25): 9552–9555. doi:10.1021/jo061949s.
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