(CDC)–Rhodium-Catalyzed Hydroallylation of Vinylarenes and 1,3-Dienes with AllylTrifluoroborates

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 a...

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Bibliographic Details
Published in:ACS catalysis 2019-07, Vol.9 (7), p.5881-5889
Main Authors: Marcum, Justin S, Cervarich, Tia N, Manan, Rajith S, Roberts, Courtney C, Meek, Simon J
Format: Article
Language:English
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Summary: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.
ISSN:2155-5435
2155-5435
DOI:10.1021/acscatal.9b01579