Copper-Catalyzed Regioselective Synthesis of Fluorescent Indazolo[2,3- a ]quinazolines and Their Photophysical Studies

A regioselective copper-catalyzed one-pot cyclization of 3-aminoindazoles with 2-bromobenzyl bromides has been developed under ligand-free conditions for the efficient synthesis of indazolo[2,3-a]quinazolines. This reaction proceeds through initial site-selective nucleophilic N-benzylation of the primary amine of 3-aminoindazole, followed by an Ullmann-type intramolecular C–N coupling and subsequent oxidative aromatization. This method has advantages of broad substrate scope, high functional group tolerance, and gram scalability. The synthesized compounds were characterized by spectroscopic techniques, and their photophysical properties were investigated by UV–visible and fluorescence spectroscopy. The synthesized indazole-fused quinazolines display good fluorescent properties, with quantum yields (ΦF) of up to 76% and a large Stokes shift of up to 163 nm. Product 3b also showed chemosensing properties toward picric acid.