posted on 2023-01-10, 14:35authored byJoshua
L. Zhu, Cullen R. Schull, Anthony T. Tam, Ángel Rentería-Gómez, Achyut Ranjan Gogoi, Osvaldo Gutierrez, Karl A. Scheidt
Photoinduced hydrogen atom transfer (HAT) has been developed
as
a powerful tool to generate synthetically valuable radical species.
The direct photoexcitation of ketones has been known to promote HAT
or to generate acyl radicals through Norrish-type pathways, but these
modalities remain severely limited by radical side reactions. We report
herein a catalyst- and transition metal-free method for the acylation
of C–H bonds that leverages the unique properties of stable,
isolable acyl azolium species. Specifically, acyl azolium salts are
shown to undergo an intermolecular and regioselective HAT upon LED
irradiation with a range of substrates bearing active C–H bonds
followed by C–C bond formation to afford ketones. Experimental
and computational studies support photoexcitation of the acyl azolium
followed by facile intersystem crossing to access triplet diradical
species that promote selective HAT and radical–radical cross-coupling.