Remarkable Activity of Potassium-Modified Carbon Nitride for Heterogeneous Photocatalytic Decarboxylative Alkyl/Acyl Radical Addition and Reductive Dimerization of para-Quinone Methides

Heterogeneous photocatalysis has emerged as a green and sustainable technique in organic synthesis. Developing highly effective heterogeneous photocatalysts that outperformed classical ruthenium-/iridium-based homogeneous ones for the visible-light mediated organic transformations is actively pursued by chemists but remains challenging. Herein, a modified carbon nitride-based heterogeneous photocatalytic system for both decarboxylative addition and reductive dimerization of para-quinone methides has been developed. The potassium-intercalated carbon nitride (CN-K) facile prepared by the direct KCl-induced structure remodeling of bulk g-C3N4 exhibited remarkable catalytic activity. The catalyst loading can be decreased to 0.025–0.25 mg/mL, which is significantly lower than that in homogeneous photocatalysis. Studies on the structure characterizations and photoelectric properties of CN-K and g-C3N4 imply that the enhanced activity of CN-K was attributed to its K-intercalated poly(heptazine)-based structure and existed as small lamellar nanocrystallites, thus leading to enhanced optical absorption, improved electron–hole separation, and easy dispersion in polar solvents. The heterogeneous nature and mild reaction conditions of this protocol allow for good catalyst recyclability, broad substrate scope, scale-up in a continuous flow, and applications to the valued target synthesis.