Visible Light-Promoted Metal-Free C–H Activation: Diarylketone-Catalyzed Selective Benzylic Mono- and Difluorination

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.

Simple and Clean Photoinduced Aromatic Trifluoromethylation Reaction

“…Therefore, acetone in this study essentially acts as both solvent to dissolve reactants and photosensitizer to harvest resonant photons. 38,39 The optimal wavelength and effective range for the trifluoromethylation reaction in acetone were determined by the wavelength dependence experiment. As shown in Figure 1b, the best yield of 95% (0.1 mmol scale) for 1 could be achieved under 2 h photoirradiation from a 300 W xenon lamp with a 300 nm long-pass filter (λ > 300 nm).…”

Cooperative dual palladium/silver catalyst for direct difluoromethylation of aryl bromides and iodides

“…Since these reactions were conducted under harsh reaction conditions and various functional groups were not compatible, many efforts have been made towards the development of alternative ways to introduce the difluoromethyl group into the desired position of the aromatic rings. Difluorination of benzylic C-H bonds that was promoted by visible light or silver catalyst generated difluoromethylarenes efficiently, yet selectivity is problematic for multi-alkylated arenes [13][14][15] . Baran and coworkers 16,17 reported a radical difluoromethylation of heteroarenes with zinc difluoromethanesulfinate, but reactions with arenes have not been reported.…”

Efficient and Chemoselective Deprotection of N-t-Butyloxycarbonyl Group Mediated by Selectfluor

“…As a continuing interest in stereoselectively fluorinated compounds, [7] recently we conducted the photo-catalyzed benzylic fluorination developed by Chen and co-workers, [8] using di-Boc protected phenyl alanine 1 as the substrate. To our surprise, no desired product 3 was observed after 24 h, but the Boc deprotected compound 2 was obtained instead in low yield (Eq.…”

“…Based on the unexpected observation when conducting the Chen's procedure for the benzylic fluorination of 1, [8] It has been found for the first time that selectfluor could selectively remove a Boc group from doubly protected amines in acetonitrile. This deprotection could be of interest when compared to other reported methods,…”