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Mechanistic-Insight-Driven Rate Enhancement of Asymmetric Copper-Catalyzed 1,4-Addition of Dialkylzinc Reagents to Enones

Nouch, Ryan; Woodward, Simon; Willcox, Darren; Robinson, David; Lewis, William

Mechanistic-Insight-Driven Rate Enhancement of Asymmetric Copper-Catalyzed 1,4-Addition of Dialkylzinc Reagents to Enones Thumbnail


Authors

Ryan Nouch

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SIMON WOODWARD simon.woodward@nottingham.ac.uk
Professor of Synthetic Organic Chemistry

Darren Willcox

David Robinson

William Lewis



Abstract

Combination of [Cu(MeCN)4]TFA•TFAH (TFA = O2CCF3) with Feringa's phosphoramidite ligand (LA) provides an exceptionally active (0.75 mol%) catalyst for asymmetric conjugate additions of ZnR2 (R = Et, Me at-40 to-80 o C) to enones. Kinetic and other studies of the addition of ZnEt2 to cyclohex-2-en-1-one indicate a transition state stoichiometry composition: (ZnEt2)3(enone)4Cu2(LA)3 that is generated by transmetalation from Et2Zn(enone)2. Catalyst genesis is significantly slower than turnover (which has limited previous attempts to attain useful kinetic data); in the initial stages varying populations of catalytically inactive, off-cycle, species are present. These issues are overcome by a double-dosing kinetic analysis protocol. A rest state of [LACu(Et)(µ-TFA)(µ-{(enone)(ZnEt)2(enolate)})CuLA2] + (through the equivalence of enolate = enone + ZnEt2) is supported by DFT studies (B3LYP/6-31G*). Rate determining ZnEt2(enone)2 transmetalation
drives the exceptionally high catalytic activity of this system.

Citation

Nouch, R., Woodward, S., Willcox, D., Robinson, D., & Lewis, W. (2020). Mechanistic-Insight-Driven Rate Enhancement of Asymmetric Copper-Catalyzed 1,4-Addition of Dialkylzinc Reagents to Enones. Organometallics, 39(6), 834-840. https://doi.org/10.1021/acs.organomet.0c00005

Journal Article Type Article
Acceptance Date Feb 20, 2020
Online Publication Date Mar 3, 2020
Publication Date Mar 23, 2020
Deposit Date Mar 3, 2020
Publicly Available Date Mar 29, 2024
Journal Organometallics
Print ISSN 0276-7333
Electronic ISSN 1520-6041
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 39
Issue 6
Pages 834-840
DOI https://doi.org/10.1021/acs.organomet.0c00005
Keywords Inorganic Chemistry; Organic Chemistry; Physical and Theoretical Chemistry
Public URL https://nottingham-repository.worktribe.com/output/4082308
Publisher URL https://pubs.acs.org/doi/abs/10.1021/acs.organomet.0c00005

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