Organocatalyzed Birch Reduction Driven by Visible Light

J Am Chem Soc. 2020 Aug 5;142(31):13573-13581. doi: 10.1021/jacs.0c05899. Epub 2020 Jul 28.

Abstract

The Birch reduction is a powerful synthetic methodology that uses solvated electrons to convert inert arenes to 1,4-cyclohexadienes-valuable intermediates for building molecular complexity. Birch reductions traditionally employ alkali metals dissolved in ammonia to produce a solvated electron for the reduction of unactivated arenes such as benzene (Ered < -3.42 V vs SCE). Photoredox catalysts have been gaining popularity in highly reducing applications, but none have been reported to demonstrate reduction potentials powerful enough to reduce benzene. Here, we introduce benzo[ghi]perylene imides as new organic photoredox catalysts for Birch reductions performed at ambient temperature and driven by visible light from commercially available LEDs. Using low catalyst loadings (<1 mol percent), benzene and other functionalized arenes were selectively transformed to 1,4-cyclohexadienes in moderate to good yields in a completely metal-free reaction. Mechanistic studies support that this unprecedented visible-light-induced reactivity is enabled by the ability of the organic photoredox catalyst to harness the energy from two visible-light photons to affect a single, high-energy chemical transformation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Benzene Derivatives / chemistry*
  • Catalysis
  • Cyclohexenes / chemistry*
  • Imides / chemistry*
  • Light*
  • Molecular Structure
  • Oxidation-Reduction
  • Perylene / analogs & derivatives*
  • Perylene / chemistry
  • Photochemical Processes

Substances

  • Benzene Derivatives
  • Cyclohexenes
  • Imides
  • 1,4-cyclohexadiene
  • Perylene
  • 1,12-benzoperylene