A Recyclable Rh(III)‐Catalyzed C−H Annulation of N‐Pyrimidinyl Aryl Amines with Cyclic 1,3‐Diones in Water

Rh(III)‐catalyzed synthesis of N‐heterocycles via regioselective C−H bond activation is both highly efficient and atom‐economical but often hindered by the use of toxic solvents and limited catalyst recyclability. Herein, we present a recyclable Rh(III)‐catalyzed C−H annulation of N‐pyrimidinyl aryl amines with cyclic 1,3‐diones in water, affording tetrahydrocarbazole derivatives. The basic aqueous environment amplifies the solubility differences between the substrates and the desired product, thereby promoting efficient C−H activation and subsequent cyclization. This method showcases broad substrate compatibility, eliminates the need for pre‐synthesized iodonium ylides, and features an easy work‐up procedure alongside straightforward catalyst recovery. The Rh(III) catalyst retains its activity for at least five cycles, providing a sustainable and practical strategy for N‐heterocycle synthesis.