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.