Synthesis of triphenylamines via ligand-free selective ring-opening of benzoxazoles or benzothiazoles under superparamagnetic nanoparticle catalysis

Abstract

CuFe₂O₄ superparamagnetic nanoparticles were utilized as an effective recyclable heterogeneous catalyst for the synthesis of triphenylamines via the ligand-free selective ring-opening reaction of benzoxazoles or benzothiazoles with iodoarenes. The nano CuFe₂O₄ demonstrated noticeably higher catalytic efficiency than a series of homogeneous catalysts and heterogeneous catalysts. It was possible to separate the nano CuFe₂O₄ by using a magnet, and the recovered catalyst was reused many times while its activity could be maintained. To the best of our knowledge, this is the first example of heterogeneous catalysis for the transformation of benzoxazoles, and the transformation of benzothiazoles to triphenylamines has not been previously reported in the literature.