Multi-component one-pot synthesis of unsymmetrical dihydro-5H-indeno[1,2-b]quinolines as new pH indicators

A mild and efficient protocol for the synthesis of 7,8-dihydro-10-aryl-5H-indeno[1,2-b]quinoline-9,11-diones via a one-pot four component condensation of aromatic aldehydes, dimedone, 1,3-indandione and ammonium acetate using melamine trisulfonic acid as a catalyst in ethanol is described. The catalyst could be recycled and reused three times without significant loss of activity. Dihydro-5H-indeno[1,2-b]quinolines with stabilized zwitterionic resonance structures showed feasible application as new pH indicators. These chemosensors have a large wavelength shift (100 nm) and showed excellent sensitivity in the range of pH from 9.2 to 12.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of a new series of indenoquinoline derivatives. ► Introduction of new pH indicators in the range 9.2–12.0. ► Simple experimental procedure with no side reactions. ► High yields of the products and use of inexpensive catalyst with lower loading. ► Reusability of the catalyst.