Abstract:

α-Trifluoromethyl ketones have been identified as versatile building blocks for the synthesis of various trifluoromethyl-functionalized molecules. Although there are significant advantages in the development of methods toward direct transformations of styrenes into α-trifluoromethyl ketones, most procedures leading to α-trifluoromethyl ketones require heavy- or transition-metal-based complexes. Herein, a new method was developed for the synthesis of α-trifluoromethyl ketones via diacetyl-catalyzed photooxidative keto-trifluoromethylation of styrenes with sodium trifluorometnanesulfinate(CF₃SO₂Na) under an air atmosphere. Twenty-two α-ketone trifluoromethyl compounds were synthesized in the yields ranging from 52% to 78%. And their structures were characterized by nuclear magnetic resonance spectroscopy(NMR) and gas chromatography-mass spectrometry(GC-MS) analysis. This reaction employed the commercially available, low cost, and easy to handle langloisreagent(CF₃SO₂Na) as a CF₃-radical source, and diacetyl was used as promising low-cost radical initiators to generate CF₃ radicals from sodium trifluorometnanesulfinate efficiently. And the reaction proceeded smoothly to give the products in moderate yield with mild conditions, a simple system and good functional group tolerance. Furthermore, mechanism investigation indicated that the oxidant H₂O₂ played an important role in promoting the photocatalytic cycle process. This photochemical strategy employed diacetyl, instead of expensive metal catalysis, proved to be a greener route to synthesize α-trifluoromethyl ketones compounds.

Key words: Olefins, 2,3-Butanedione, Photocatalytic, Oxidative trifluoromethylation, Free radical