Journal of the American Chemical Society 2013-11-20

Visible light-promoted metal-free C-H activation: diarylketone-catalyzed selective benzylic mono- and difluorination.

Ji-Bao Xia, Chen Zhu, Chuo Chen

Index: J. Am. Chem. Soc. 135(46) , 17494-500, (2013)

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Abstract

We report herein an operationally simple method for the direct conversion of benzylic C-H groups to C-F. We show that visible light can activate diarylketones to abstract a benzylic hydrogen atom selectively. Adding a fluorine radical donor yields the benzylic fluoride and regenerates the catalyst. The selective formation of mono- and difluorination products can be achieved by catalyst control. 9-Fluorenone catalyzes benzylic C-H monofluorination, while xanthone catalyzes benzylic C-H difluorination. The scope and efficiency of this new C-H fluorination method are significantly better than those of the existing methods. This is also the first report of selective C-H gem-difluorination.