Thioxanthone-based ionic liquid as photocatalyst for a tandem cyclization reaction to synthesize pyrroloquinolinones

Visible light catalysis provides an important platform for developing green and sustainable catalytic processes. However, traditional photosensitizers have limited their application due to their inherent limitations. Due to the structural stability and recyclability of ionic liquids (ILs), a bifunctional catalyst TXIL-Ni was designed and synthesized by introducing the photosensitizer thioxanthone (TX) and transition metal Ni(II) into ILs. TXIL-Ni exhibited remarkable photocatalytic activity for C7–H acylation of indolines to efficiently synthesize pyrroloquinolinone derivatives by a tandem cyclization reaction of decarboxylation acylation and Claisen-Schmidt condensation. The protocol provided a new strategy for the synthesis of the natural product Viridicatol and the key intermediate of farnesyltransferase inhibitors. The experimental results indicated that thioxanthone-based ionic liquid TXIL-Ni as a synergistic photocatalyst has the advantages of mild reaction conditions, recyclability, and atomic economy. This provides a new solution for the design of multifunctional and reusable catalysts.