4.7 Article

Photocatalytic redox-neutral reaction of γ-indolyl α-keto esters

Journal

ORGANIC CHEMISTRY FRONTIERS
Volume 9, Issue 7, Pages 1875-1883

Publisher

ROYAL SOC CHEMISTRY
DOI: 10.1039/d1qo01890f

Keywords

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Funding

  1. Taishan Scholars Construction Projects of Shandong [tsqn201812075]
  2. Natural Science Foundation of Shandong Province for Distinguished Young Scholars [ZR2020JQ07]
  3. Youth Innovation Science and Technology Plan of Colleges and Universities in Shandong Province [2019KJC003]
  4. Natural Science Foundation of China [21801007]
  5. Natural Science Foundation of Shandong Province, China [ZR2019PB020, ZR2016JL012]
  6. Qingdao University of Science Technology

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Photoredox catalysis involving Ir-III in combination with DABCO as a dual hydrogen-bonding donor and organic base can enable the direct gamma-C(sp(3))-H activation of saturated alpha-keto esters, leading to the synthesis of various 4-indolyl substituted 2-hydroxy-3-enoic acid esters. This method offers high yields and high enantioselectivity.
The direct gamma-C(sp(3))-H activation of saturated alpha-keto esters has long been an elusive transformation. We found that photoredox catalysis involving Ir-III in combination with DABCO as a dual hydrogen-bonding donor and organic base can lead to the transient generation of the multi-pi-electron gamma-enolyl radical from gamma-indolyl alpha-keto ester via enolization, oxidation and gamma-deprotonation. In the spin delocalized system, the gamma-enolyl radical can be easily reduced by Ir-II to form the gamma-enolyl anion and subsequently couple with a proton at the alpha-position of the ester. This mode of activation is suitable for the synthesis of various 4-indolyl substituted 2-hydroxy-3-enoic acid esters (in up to 90% yield and with up to Z/E >96 : 4) and is amenable for enantioselective catalysis.

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