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.

共轭加成反应，作为一种在合成化学中极为有用的碳-碳键形成反应，通常需要反应性碳亲核试剂以实现加成。自由基共轭加成提供了一种途径，用以替代反应性亲核试剂，而采用便捷的自由基前体。通过脱羧反应，羧酸可以作为简单且稳定的自由基前体，但通常需要将其活化成反应性酯以促进艰难的脱羧过程。在本研究中，我们报道了一种直接、双催化脱羧自由基共轭加成反应，适用于广泛范围的羧酸，该反应无需酸预处理，并得益于可见光驱动的阿的宁光催化与高效的铜催化循环的结合。机理研究和计算研究为我们揭示了配体和金属物种在双催化过程中的作用，以及取代阿的宁的光催化活性。