Acridine Photocatalysis: Insights into the Mechanism and Development of a Dual-Catalytic Direct Decarboxylative Conjugate Addition

Conjugate addition
is one of the most synthetically useful carbon–carbon bond-forming
reactions; however, reactive carbon nucleophiles are typically required
to effect the addition. Radical conjugate addition provides an avenue
for replacing reactive nucleophiles with convenient radical precursors.
Carboxylic acids can serve as simple and stable radical precursors
by way of decarboxylation, but activation to reactive esters is typically
necessary to facilitate the challenging decarboxylation. Here, we
report a direct, dual-catalytic decarboxylative radical conjugate
addition of a wide range of carboxylic acids that does not require
acid preactivation and is enabled by the visible light-driven acridine
photocatalysis interfaced with an efficient copper catalytic cycle.
Mechanistic and computational studies provide insights into the roles
of the ligands and metal species in the dual-catalytic process and
the photocatalytic activity of substituted acridines.