Mechanistic-insight-driven rate enhancement of asymmetric copper-catalyzed 1,4-addition of dialkylzinc reagents to enones

Nouch, R., Woodward, S., Willcox, D., Robinson, D. ORCID: 0000-0003-2760-7163 and Lewis, W., 2020. Mechanistic-insight-driven rate enhancement of asymmetric copper-catalyzed 1,4-addition of dialkylzinc reagents to enones. Organometallics, 39 (6), pp. 834-840. ISSN 0276-7333

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Abstract

The 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 and Me at −40 to −80 °C) to enones. Kinetic and other studies of the addition of ZnEt2 to cyclohex-2-en-1-one indicate a transition state stoichiometry composition of (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-dose 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 (ωB97X-D/SRSC). Rate-determining ZnEt2(enone)2 transmetalation drives the exceptionally high catalytic activity of this system.

Item Type: Journal article
Publication Title: Organometallics
Creators: Nouch, R., Woodward, S., Willcox, D., Robinson, D. and Lewis, W.
Publisher: American Chemical Society
Date: 2020
Volume: 39
Number: 6
ISSN: 0276-7333
Identifiers:
NumberType
10.1021/acs.organomet.0c00005DOI
1302274Other
Divisions: Schools > School of Science and Technology
Depositing User: Jonathan Gallacher
Date Added: 17 Mar 2020 16:58
Last Modified: 22 Apr 2020 13:14
URI: http://irep.ntu.ac.uk/id/eprint/39409

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