AgSCN/(NH₄)₂S₂O₈-Promoted Cascade Cyclization of 1-(2-Ethynylphenyl)-1H-indoles and Derivatives

Described herein is an efficient and novel method for the synthesis of 6-arylindolo[1,2-a]quinoline-5,7-diones from 1-(2-ethynylphenyl)-1H-indoles. The reaction readily proceeded via a tandem process, leading to the desired products in moderate yields. The reaction can accommodate a broad range of functional groups and is efficient on a gram-scale synthesis. Under standard reaction conditions, 4-phenylpyrrolo[1,2-a]quinoline-3,5-dione can be readily accessed by using 1-(2-(phenylethynyl)phenyl)-1H-pyrrole as a substrate. The single-crystal X-ray diffraction data confirm the chemical structure of the product. Photophysical properties of some selected 6-arylindolo[1,2-a]quinoline-5,7-diones were studied by UV–visible and fluorescence spectroscopy.