EPR studies on the addition of ligated boryl radicals to carbonyl compounds

John C. Walton, Wen Dai, Dennis P. Curran

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8 Citations (Scopus)
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The boron-centered radicals derived from alkenyl N-heterocyclic carbene (NHC)-boranes bearing ester substituents were recently found to ring close in 5-endo mode by addition to the oxygen atoms of the ester substituents. The inference from this was that NHC-boryl radicals might add intermolecularly to carbonyl-containing substrates. Several different NHC-boryl radicals were generated by H-atom abstraction from NHC-ligated trihydroborates. Electron paramagnetic resonance (EPR) spectroscopy proved that these did indeed add to the oxygen atoms of diaryl ketones with production of the corresponding bora-ketyl radicals. The same unusual regioselectivity of addition was observed with monoaryl ketones, but no bora-ketyls were observed with dialkyl ketones. Similarly, no bora-ketyl adduct radicals were observed with esters, even esters of benzoic acid. EPR spectroscopic evidence suggested that NHC-boryl radicals were also added to the O-atoms of aromatic aldehydes. Amine-boryl and phosphine-boryl radicals were also observed to add to the O-atom of benzophenone with production of the corresponding ketyl radicals.
Original languageEnglish
Pages (from-to)4248-4255
Number of pages8
JournalThe Journal of Organic Chemistry
Issue number6
Early online date14 Feb 2020
Publication statusPublished - 20 Mar 2020


  • Hydrocarbons
  • Adducts
  • Ketones
  • Electron paramagnetic resonance spectroscopy
  • Aromatic compounds


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