An unprecedented photocatalytic system
consisting of benzimidazolium
aryloxide betaines (BI+–ArO–)
and stoichiometric hydride reducing reagents was developed for carrying
out desulfonylation reactions of N-sulfonyl-indoles,
-amides, and -amines, and α-sulfonyl ketones. Measurements of
absorption spectra and cyclic voltammograms as well as density functional
theory (DFT) calculations were carried out to gain mechanistic information.
In the catalytic system, visible-light-activated benzimidazoline aryloxides
(BIH–ArO–), generated in situ by hydride
reduction of the corresponding betaines BI+–ArO–, donate both an electron and a hydrogen atom to the
substrates. A modified protocol was also developed so that a catalytic
quantity of more easily prepared hydroxyaryl benzimidazolines (BIH–ArOH)
is used along with a stoichiometric hydride donor to promote the photochemical
desulfonylation reactions.