Four-Component Synthesis of Spiro-Imidazolidines Enabled by Carbon Nitride Photocatalysis

Metal-free heterogeneous catalysis provides a promising strategy for the multicomponent synthesis of valuable imidazolidines, which are ubiquitous structural moieties found in a variety of pharmaceuticals, agrochemicals, and ligands. The design of robust and cost-effective catalysts is the key to this route. Herein, we report the preparation of photocatalytically active and carbon nitride-based heterogeneous catalysts from melamine and glyoxal. It was found that the obtained catalyst (denoted as 1.0 Ci-C₃N₄) shows visible light harvesting capacity and catalytic activity owing to its partially distorted heptazine-based structure. Importantly, the utilization of this developed heterogeneous photocatalyst enables the four-component synthesis of spiro-imidazolidines under visible light irradiation, starting from simple amines, cyclic ketones, amino acids, and aldehydes. This protocol exhibits a broad substrate scope and good functional group tolerance. Furthermore, the heterogeneous nature of the 1.0 Ci-C₃N₄ catalytic system allows easy recovery, catalyst recycling, and the use in multiple runs without loss of activity, as well as gram scale synthesis in continuous photo flow fashion, thus implying the great potential of use in industrial manufacture.