Mild, rapid and efficient metal-free synthesis of 2-aryl-4-aryloxyquinolines via direct Csp2-O bond formation by using diaryliodonium salts

An efficient ligand- and transition metal-free procedure for the direct C-sp(2)-O bond formation for the arylation of 2-aryl-4-quinolones was developed. The synthesis of the starting quinolones was carried out under our optimized Cu-catalyzed C-N bond formation conditions between 2'-bromoacetophenone and benzamide derivatives followed by cyclization. Easily prepared diaryliodonium salts were used as aryl source. Highly functionalized 4-aryloxyquinolines were obtained in a mild and operationally simple protocol, which involves conventional heating and short periods of time. The method shows good to excellent yields and broad toleration of functional groups like fluorine or trifluoromethyl, which are important in medicinal chemistry. The C-sp(2)-O bond formation process herein described for the quinolone functionalization offers an excellent non-toxic alternative to the transition metal-catalyzed reactions that not only can potentially contaminate the final compounds but also can be environmental pollutants. (C) 2016 Elsevier Ltd. All rights reserved.