Synthesis of indolo- and benzothieno[3,2-c]quinolines via POCl<inf>3</inf> mediated tandem cyclization of o-alkynylisocyanobenzenes derived from o-alkynyl-N-phenylformamides

Abstract

A synthesis of indolo[3,2-c]quinolines and benzothieno[3,2-c]quinolines has been developed employing o-alkynyl-N-phenylformamide derivatives as the substrates. The reaction proceeded via a tandem process involving POCl3-assisted intramolecular cyclization of the firstly formed o-alkynylisocyanobenzenes, leading to the desired products in moderate to high yields. Furthermore, the reaction is efficient on a gram-scale and the products were structurally modified by amination, Suzuzki-Miyaura reaction and Heck cross-coupling. Photophysical properties of several selected indolo[3,2-c]quinolines were studied by UV-Visible and fluorescence spectroscopy and rationalized using time-dependent DFT calculations.