EPR studies on the addition of ligated boryl radicals to carbonyl compounds
Abstract
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.
Citation
Walton , J C , Dai , W & Curran , D P 2020 , ' EPR studies on the addition of ligated boryl radicals to carbonyl compounds ' , The Journal of Organic Chemistry , vol. 85 , no. 6 , pp. 4248-4255 . https://doi.org/10.1021/acs.joc.9b03420
Publication
The Journal of Organic Chemistry
Status
Peer reviewed
ISSN
0022-3263Type
Journal article
Description
J.C.W. thanks EaStCHEM for financial support and D.P.C. thanks the US National Science Foundation. Computational support was provided through the EaStCHEM Research Computing Facility.Collections
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