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. 2019 Jan 22;10(10):3049-3053.
doi: 10.1039/c8sc05170d. eCollection 2019 Mar 14.

Transition-metal-free α-arylation of oxindoles vi a visible-light-promoted electron transfer

Kangjiang Liang  1 , Na Li  1 , Yang Zhang  1 , Tao Li  1 , Chengfeng Xia  1
Affiliations

Transition-metal-free α-arylation of oxindoles vi a visible-light-promoted electron transfer

Kangjiang Liang et al. Chem Sci. .

Abstract

An operationally simple photochemical strategy for the direct arylation of oxindoles with (hetero)aryl halides in the absence of both transition metals and photoredox catalysts has been developed. The reaction provides an efficient way to construct various 3-aryloxindole building blocks of pharmaceutical interest at ambient temperature by using household compact fluorescent light (CFL) bulbs as the light source. Preliminarily, mechanistic studies revealed that the intermolecular electron transfer relied on the formation of photon-absorbing electron-donor-acceptor (EDA) complexes between electron-rich oxindole enolates and electron-deficient (hetero)aryl halides, and a radical chain mechanism was operative.

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Figures

Fig. 1
Fig. 1. (a) Pharmaceutically active molecules with a 3-aryloxindole moiety. (b) Transition-metal-catalyzed α-arylation of oxindole. (c) Visible-light-promoted arylation of oxindole with an EDA complex.
Fig. 2
Fig. 2. 1H NMR spectra of 2a with different MOHs (M = Na+, K+, or Cs+) in CD3CN. (a) Full 1H NMR spectra. (b) Selected aromatic region of the 1H NMR spectral window between 7.40 and 6.40 ppm.
Fig. 3
Fig. 3. Mechanistic studies: (a) UV/Vis absorption spectra of acetonitrile solutions (0.1 M) of 1a (i), 2a (ii), mixture of 1a and 2a (iii), mixture of 1a and CsOH (iv), mixture of 2a and CsOH (v), and mixture of 1a, 2a and CsOH (iv). (b) Long wavelength experiment. (c) Intramolecular radical clock experiment.
Scheme 1
Scheme 1. Proposed mechanism for visible-light-promoted arylation.
See this image and copyright information in PMC

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