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Photoinduced, Copper-Catalyzed Alkylation of Amines: A Mechanistic Study of the Cross-Coupling of Carbazole with Alkyl Bromides

Ahn, Jun Myun and Ratani, Tanvi S. and Hannoun, Kareem I. and Fu, Gregory C. and Peters, Jonas C. (2017) Photoinduced, Copper-Catalyzed Alkylation of Amines: A Mechanistic Study of the Cross-Coupling of Carbazole with Alkyl Bromides. Journal of the American Chemical Society, 139 (36). pp. 12716-12723. ISSN 0002-7863. PMCID PMC5685493. https://resolver.caltech.edu/CaltechAUTHORS:20170818-105931485

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Abstract

We have recently reported that a variety of couplings of nitrogen, sulfur, oxygen, and carbon nucleophiles with organic halides can be achieved under mild conditions (−40 to 30 °C) through the use of light and a copper catalyst. Insight into the various mechanisms by which these reactions proceed may enhance our understanding of chemical reactivity and facilitate the development of new methods. In this report, we apply an array of tools (EPR, NMR, transient absorption, and UV–vis spectroscopy; ESI–MS; X-ray crystallography; DFT calculations; reactivity, stereochemical, and product studies) to investigate the photoinduced, copper-catalyzed coupling of carbazole with alkyl bromides. Our observations are consistent with pathways wherein both an excited state of the copper(I) carbazolide complex ([Cu^I(carb)_2]^−) and an excited state of the nucleophile (Li(carb)) can serve as photoreductants of the alkyl bromide. The catalytically dominant pathway proceeds from the excited state of Li(carb), generating a carbazyl radical and an alkyl radical. The cross-coupling of these radicals is catalyzed by copper via an out-of-cage mechanism in which [Cu^I(carb)_2]^− and [Cu^(II)(carb)_3]^− (carb = carbazolide), both of which have been identified under coupling conditions, are key intermediates, and [Cu^(II)(carb)_3]^− serves as the persistent radical that is responsible for predominant cross-coupling. This study underscores the versatility of copper(II) complexes in engaging with radical intermediates that are generated by disparate pathways, en route to targeted bond constructions.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/jacs.7b07052DOIArticle
https://pubs.acs.org/doi/suppl/10.1021/jacs.7b07052PublisherSupporting Information
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5685493PubMed CentralArticle
ORCID:
AuthorORCID
Fu, Gregory C.0000-0002-0927-680X
Peters, Jonas C.0000-0002-6610-4414
Additional Information:© 2017 American Chemical Society. Received: July 6, 2017; Published: August 17, 2017. Support has been provided by the National Institutes of Health (National Institute of General Medical Sciences: R01–109194), the Natural Sciences and Engineering Research Council of Canada (graduate research fellowship for J.M.A.), and the National Science Foundation (support of the Caltech EPR Facility (NSF-1531940) and a graduate research fellowship for T.S.R.). Additional support has been provided by the Arnold and Mabel Beckman Foundation through the Caltech Beckman Institute Laser Resource Center. We thank Dr. Angel J. Di Bilio, Dr. Paul Oyala, Dr. Sidney E. Creutz, Lawrence M. Henling, Dr. Marcin Kalek, Dr. Wesley Sattler, Dr. Oliver S. Shafaat, Dr. Mona Shahgholi, Dr. David VanderVelde, and Dr. Jay R. Winkler for technical assistance and helpful discussions. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
NIHR01-109194
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
NSFCHE-1531940
NSF Graduate Research FellowshipUNSPECIFIED
Arnold and Mabel Beckman FoundationUNSPECIFIED
Issue or Number:36
PubMed Central ID:PMC5685493
Record Number:CaltechAUTHORS:20170818-105931485
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170818-105931485
Official Citation:Photoinduced, Copper-Catalyzed Alkylation of Amines: A Mechanistic Study of the Cross-Coupling of Carbazole with Alkyl Bromides Jun Myun Ahn, Tanvi S. Ratani, Kareem I. Hannoun, Gregory C. Fu, and Jonas C. Peters Journal of the American Chemical Society 2017 139 (36), 12716-12723 DOI: 10.1021/jacs.7b07052
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:80616
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Aug 2017 18:14
Last Modified:03 Mar 2020 19:09

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