(CDC)-Rhodium-catalyzed hydroallylation of vinylarenes and 1,3-dienes with allyltrifluoroborates

Justin S. Marcum, Tia N. Cervarich, Rajith S. Manan, Courtney C. Roberts, Simon J. Meek

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Catalytic site-selective hydroallylation of vinyl arenes and 1,3-dienes is reported. Transformations are promoted by a readily accessible bidentate carbodicarbene-rhodium complex and involve commercially available allyltrifluoroborates and an alcohol. The reaction is applicable to vinyl arenes and aryl-or alkyl-substituted 1,3-dienes (30 examples). Allyl addition products are generated in 40-78% yield and in up to >98:2 site selectivity. Reaction outcomes are consistent with the intermediacy of a Rh(III)-hydride generated by protonation of Rh(I) by an acid. A number of key mechanistic details of the reaction are presented: (1) Deuterium scrambling into the product and starting alkene indicates reversible Rh(III)-H migratory insertion. (2) A large primary kinetic isotope effect is observed. (3) With substituted allyltrifluoroborates (e.g., crotyl-BF3K) mixtures of site isomers are generated as a result of transmetalation followed by Rh-(allyl) complex equilibration, consequently disproving outer-sphere addition of the allyl nucleophile to Rh(III)-(η3-allyl). (4) Stereochemical analysis of a cyclohexadiene allyl addition product supports a syn Rh(III)-hydride addition. (5) A Hammett plot shows a negative slope. Finally, utility is highlighted by a iodocyclization and cross metathesis.

Original languageEnglish (US)
Pages (from-to)5881-5889
Number of pages9
JournalACS Catalysis
Volume9
Issue number7
DOIs
StatePublished - May 22 2019

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Rhodium
Hydrides
Nucleophiles
Deuterium
Protonation
Alkenes
Isotopes
Isomers
Olefins
Alcohols
Kinetics
Acids
1,4-cyclohexadiene

Keywords

  • alkene
  • allyltrifluoroborates
  • carbodicarbene ligands
  • hydroallylation
  • rhodium catalysis

Cite this

(CDC)-Rhodium-catalyzed hydroallylation of vinylarenes and 1,3-dienes with allyltrifluoroborates. / Marcum, Justin S.; Cervarich, Tia N.; Manan, Rajith S.; Roberts, Courtney C.; Meek, Simon J.

In: ACS Catalysis, Vol. 9, No. 7, 22.05.2019, p. 5881-5889.

Research output: Contribution to journalArticle

Marcum, Justin S. ; Cervarich, Tia N. ; Manan, Rajith S. ; Roberts, Courtney C. ; Meek, Simon J. / (CDC)-Rhodium-catalyzed hydroallylation of vinylarenes and 1,3-dienes with allyltrifluoroborates. In: ACS Catalysis. 2019 ; Vol. 9, No. 7. pp. 5881-5889.
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AU - Marcum, Justin S.

AU - Cervarich, Tia N.

AU - Manan, Rajith S.

AU - Roberts, Courtney C.

AU - Meek, Simon J.

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N2 - Catalytic site-selective hydroallylation of vinyl arenes and 1,3-dienes is reported. Transformations are promoted by a readily accessible bidentate carbodicarbene-rhodium complex and involve commercially available allyltrifluoroborates and an alcohol. The reaction is applicable to vinyl arenes and aryl-or alkyl-substituted 1,3-dienes (30 examples). Allyl addition products are generated in 40-78% yield and in up to >98:2 site selectivity. Reaction outcomes are consistent with the intermediacy of a Rh(III)-hydride generated by protonation of Rh(I) by an acid. A number of key mechanistic details of the reaction are presented: (1) Deuterium scrambling into the product and starting alkene indicates reversible Rh(III)-H migratory insertion. (2) A large primary kinetic isotope effect is observed. (3) With substituted allyltrifluoroborates (e.g., crotyl-BF3K) mixtures of site isomers are generated as a result of transmetalation followed by Rh-(allyl) complex equilibration, consequently disproving outer-sphere addition of the allyl nucleophile to Rh(III)-(η3-allyl). (4) Stereochemical analysis of a cyclohexadiene allyl addition product supports a syn Rh(III)-hydride addition. (5) A Hammett plot shows a negative slope. Finally, utility is highlighted by a iodocyclization and cross metathesis.

AB - Catalytic site-selective hydroallylation of vinyl arenes and 1,3-dienes is reported. Transformations are promoted by a readily accessible bidentate carbodicarbene-rhodium complex and involve commercially available allyltrifluoroborates and an alcohol. The reaction is applicable to vinyl arenes and aryl-or alkyl-substituted 1,3-dienes (30 examples). Allyl addition products are generated in 40-78% yield and in up to >98:2 site selectivity. Reaction outcomes are consistent with the intermediacy of a Rh(III)-hydride generated by protonation of Rh(I) by an acid. A number of key mechanistic details of the reaction are presented: (1) Deuterium scrambling into the product and starting alkene indicates reversible Rh(III)-H migratory insertion. (2) A large primary kinetic isotope effect is observed. (3) With substituted allyltrifluoroborates (e.g., crotyl-BF3K) mixtures of site isomers are generated as a result of transmetalation followed by Rh-(allyl) complex equilibration, consequently disproving outer-sphere addition of the allyl nucleophile to Rh(III)-(η3-allyl). (4) Stereochemical analysis of a cyclohexadiene allyl addition product supports a syn Rh(III)-hydride addition. (5) A Hammett plot shows a negative slope. Finally, utility is highlighted by a iodocyclization and cross metathesis.

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