Catalytic Synthesis of Indolines by Hydrogen Atom Transfer to Cobalt(III)–Carbene Radicals

We report a new method for the synthesis of indolines from o‐aminobenzylidine N‐tosylhydrazones proceeding through a cobalt(III)–carbene radical intermediate. This methodology employs the use of inexpensive commercially available reagents and allows for the transformation of easily derivatized benza...

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Bibliographic Details
Published in:Chemistry : a European journal Vol. 24; no. 20; pp. 5253 - 5258
Main Authors: Karns, Alexander S., Goswami, Monalisa, de Bruin, Bas
Format: Journal Article
Language:English
Published: WEINHEIM Wiley 06.04.2018
Wiley Subscription Services, Inc
John Wiley and Sons Inc
Subjects:
Aniline
Benzaldehyde
carbenes
Catalysis
Chemical synthesis
Chemistry
Chemistry, Multidisciplinary
Cobalt
Computer applications
Density functional theory
Heterocyclic compounds
indolines
Intermediates
metalloradicals
Nitrogen
Physical Sciences
Precursors
Radicals
Reagents
Science & Technology
indolines
SUBSTITUTED INDOLINES
C(SP)-H BONDS
radicals
carbenes
cobalt
N-TOSYLHYDRAZONES
MEDIATED INTRAMOLECULAR AMINATION
ASYMMETRIC CYCLOPROPANATION
metalloradicals
METALLORADICAL CATALYSIS
CARBENE COMPLEXES
ARYL AMINATION
C-H INSERTION
ELECTRONIC-STRUCTURE
ISSN:0947-6539, 1521-3765, 1521-3765
Online Access:Get full text
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Summary:We report a new method for the synthesis of indolines from o‐aminobenzylidine N‐tosylhydrazones proceeding through a cobalt(III)–carbene radical intermediate. This methodology employs the use of inexpensive commercially available reagents and allows for the transformation of easily derivatized benzaldehyde‐derived precursors to functionalized indoline products. This transformation takes advantage of the known propensity of radicals to undergo rapid intramolecular 1,5‐hydrogen atom transfer (1,5‐HAT) to form more stabilized radical intermediates. Computational investigations using density functional theory identify remarkably low barriers for 1,5‐HAT and subsequent radical rebound displacement, providing support for the proposed mechanism. We explore the effect of a variety of nitrogen substituents, and highlight the importance of adequate resonance stabilization of radical intermediates to the success of the transformation. Furthermore, we evaluate the steric and electronic effects of substituents on the aniline ring. This transformation is the first reported example of the synthesis of nitrogen‐containing heterocycles from cobalt(III)–carbene radical precursors. A radical new method for indoline synthesis exploits the propensity of cobalt(III)‐carbene radicals to facilitate 1,5‐hydrogen atom transfer. This article discusses reaction optimization, highlights scope and limitations, and provides computational support for the proposed mechanism.
Bibliography:These authors contributed equally to this work.
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ISSN:0947-6539
1521-3765
1521-3765
DOI:10.1002/chem.201704626