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Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation

[Image: see text] Although nickel-catalyzed stereoconvergent couplings of racemic alkyl electrophiles are emerging as a powerful tool in organic chemistry, to date there have been no systematic mechanistic studies of such processes. Herein, we examine the pathway for enantioselective Negishi arylati...

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Autores principales: Schley, Nathan D., Fu, Gregory C.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2014
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4277758/
https://www.ncbi.nlm.nih.gov/pubmed/25402209
http://dx.doi.org/10.1021/ja508718m
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author Schley, Nathan D.
Fu, Gregory C.
author_facet Schley, Nathan D.
Fu, Gregory C.
author_sort Schley, Nathan D.
collection PubMed
description [Image: see text] Although nickel-catalyzed stereoconvergent couplings of racemic alkyl electrophiles are emerging as a powerful tool in organic chemistry, to date there have been no systematic mechanistic studies of such processes. Herein, we examine the pathway for enantioselective Negishi arylations of secondary propargylic bromides, and we provide evidence for an unanticipated radical chain pathway wherein oxidative addition of the C–Br bond occurs through a bimetallic mechanism. In particular, we have crystallographically characterized a diamagnetic arylnickel(II) complex, [(i-Pr-pybox)Ni(II)Ph]BAr(F)(4), and furnished support for [(i-Pr-pybox)Ni(II)Ph](+) being the predominant nickel-containing species formed under the catalyzed conditions as well as a key player in the cross-coupling mechanism. On the other hand, our observations do not require a role for an organonickel(I) intermediate (e.g., (i-Pr-pybox)Ni(I)Ph), which has previously been suggested to be an intermediate in nickel-catalyzed cross-couplings, oxidatively adding alkyl electrophiles through a monometallic pathway.
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spelling pubmed-42777582015-11-17 Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation Schley, Nathan D. Fu, Gregory C. J Am Chem Soc [Image: see text] Although nickel-catalyzed stereoconvergent couplings of racemic alkyl electrophiles are emerging as a powerful tool in organic chemistry, to date there have been no systematic mechanistic studies of such processes. Herein, we examine the pathway for enantioselective Negishi arylations of secondary propargylic bromides, and we provide evidence for an unanticipated radical chain pathway wherein oxidative addition of the C–Br bond occurs through a bimetallic mechanism. In particular, we have crystallographically characterized a diamagnetic arylnickel(II) complex, [(i-Pr-pybox)Ni(II)Ph]BAr(F)(4), and furnished support for [(i-Pr-pybox)Ni(II)Ph](+) being the predominant nickel-containing species formed under the catalyzed conditions as well as a key player in the cross-coupling mechanism. On the other hand, our observations do not require a role for an organonickel(I) intermediate (e.g., (i-Pr-pybox)Ni(I)Ph), which has previously been suggested to be an intermediate in nickel-catalyzed cross-couplings, oxidatively adding alkyl electrophiles through a monometallic pathway. American Chemical Society 2014-11-17 2014-11-26 /pmc/articles/PMC4277758/ /pubmed/25402209 http://dx.doi.org/10.1021/ja508718m Text en Copyright © 2014 American Chemical Society This is an open access article published under an ACS AuthorChoice License (http://pubs.acs.org/page/policy/authorchoice_termsofuse.html) , which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
spellingShingle Schley, Nathan D.
Fu, Gregory C.
Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation
title Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation
title_full Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation
title_fullStr Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation
title_full_unstemmed Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation
title_short Nickel-Catalyzed Negishi Arylations of Propargylic Bromides: A Mechanistic Investigation
title_sort nickel-catalyzed negishi arylations of propargylic bromides: a mechanistic investigation
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4277758/
https://www.ncbi.nlm.nih.gov/pubmed/25402209
http://dx.doi.org/10.1021/ja508718m
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