Photoredox ketone catalysis for the direct C–H imidation and acyloxylation of arenes† †Electronic supplementary information (ESI) available: Experimental procedures and characterization data for all relevant compounds. CCDC 1544882. For ESI and crystallographic data in CIF or other electronic format

Using a tuned yet simple catalyst, the photoexcited ketone-catalyzed C–H imidation and acyloxylation of arenes through an oxidative quenching cycle has been developed.

The spectral data of remaining imidation reagents are in agreement with those reported in the literature. 3

Effect of Concentration
The optimization of substrate concentration revealed that 0.1 M and 0.05 M were equally efficient.

Effect of Imidating Agent
We envisioned that the imidating agents with electron-withdrawing groups might be appropriate for this direct C-H imidation of arenes. With this premise in mind, several imidating agents with different leaving ability of carboxylate anion were synthesized and screened. As shown above, the results were obtained on the expected lines. The reactions of 1a with imidating agents possessing 4-(trifluoromethyl)phenyl and trifluoromethyl groups, which were utilized by Sanford and coworkers, 3 afforded the product 3a in good yields. At this point, we prepared 3,5bis(trifluoromethyl)phenyl-substituted 2 and its use for the imidation of 1a led to the production of 3a in 98% yield. It is important to note that unlike other imidating agents, 2 can be stored at room temperature for months without any deterioration. The reaction mixture was irradiated at fixed intervals. As evident from the data listed in the above Table, the reaction proceeded only in the presence of light. This result showed that light is essential for the reaction and it also provided a preliminary support for the absence of a radical chain process, which was later confirmed by a low quantum yield of 0.036 (see page S-19).

Effect of Light Intensity
The reaction relied upon the intensity of the 365 nm LED. As summarized in the above scheme, when the reaction mixture was irradiated at 500W/m 2 , low conversion (75%) was observed, whereas the imidation proceeded smoothly with the intensity of 1000 W/m 2 and 1500 W/m 2 . Unless otherwise stated, all reactions in this study are carried out with the intensity of 1500 W/m 2 .

Recovery of the Acid
In the C-H imidation of 1a using 2, 3,5-bis(trifluoromethyl)benzoic acid was recovered in 99% NMR yield. This experiment corroborates the generation of a 3,5-bis(trifluoromethyl)benzoate anion in the catalytic cycle rather than the corresponding radical that would be susceptible towards decarboxylation to eventually form 1,3-bis(trifluoromethyl)benzene.
The point described above was further confirmed by carrying out the C-H imidation of 1a with the imidating agent introduced by Sanford, 3 which furnished 3a in 64% yield and trifluoroacetic acid (TFA) in 97% NMR yield. The generation of TFA in an amount larger than that of 3a can be accounted for by the hydrolysis of the moisture sensitive imidating agent. This outcome supports the generation of trifluoroacetate anion in the catalytic cycle rather than trifluoroacetate radical that is known to undergo rapid decarboxylation to generate the trifluoromethyl radical. 4

Triplet Lifetime of Ketones (τ) and Catalytic Activity
The screening of ketones with different τ values in the imidation of 1a with 2 (triplet energy: 310.7 kJ/mol) under the conditions described for Table 1 (main text) showed no direct correlation between τ and catalytic activity. As seen in the above scheme, 4,4'-dimethoxybenzophenone was significantly less active than more electron-rich Michler's ketone that has shorter triplet lifetime and lower triplet 4. J. W. Beatty, J. J. Douglas, K. P. Cole and C. R. J. Stephenson, Nat. Commun., 2015, 6, 7919 energy. 5 Because of the difficulty associated with further modifications of Michler's ketone and presumed instability of the resulting even more electron-rich ketones under the reaction conditions, we decided to proceed toward structural tuning of thioxanthone framework for reactivity enhancement.

E. Photoexcited Ketone-Catalyzed C-H Imidation of Arenes:
General procedure for the ketone-catalyzed C-H imidation of arenes: In a flame and vacuum dried reaction tube, 2 (40.3 mg, 0.1 mmol, 1.0 equiv) and XI were taken. The reaction flask was degassed in vacuo and backfilled with argon. To the mixture CH 3 CN (1.0 mL) and arene (1.0 mmol, 10.0 equiv) were added. The resulting solution was stirred at 25 °C under 365 nm irradiation (1500 W/m 2 ) for 15 h. The reaction was quenched by adding a saturated aqueous solution of NaHCO 3 (5 mL). The aqueous phase was extracted with CH 2 Cl 2 (3 × 10 mL) and the combined organic phase was dried over anhydrous Na 2 SO 4 , concentrated under reduced pressure. Purification of the residue by column chromatography over silica gel afforded 3. 3a: Following the general procedure described above with XI (2.7 mg, 0.01 mmol, 0.1 equiv) and benzotrifluoride (0.122 mL, 1.0 mmol, 10.0 equiv) as the arene source, 3a was obtained as a white solid (28.5 mg, 0.098 mmol, 98% yield, o/m/p = >0.1:2.6:1.0). The isomer ratios were determined through 19 F-NMR. The isolated product was an inseparable mixture of isomers. All peaks observed in the 1 H-NMR, 13  3e: Following the general procedure described above with XI (1.35 mg, 0.005 mmol, 0.05 equiv) and naphthalene (129.0 mg, 1.0 mmol, 10.0 equiv) as the arene source, 3e was obtained as a white solid. The crude product was obtained as a mixture of two isomers (a/b = 7:1). The isomer ratios were determined through 1 H-NMR. During purification by column chromatography, only major product was isolated (19.0 mg, 0.069 mmol, 69% yield). 3f: Following the general procedure described above with XI (1.35 mg, 0.005 mmol, 0.05 equiv) and thiophene (0.08 mL, 1.0 mmol, 10.0 equiv) as the arene source, 3f was obtained as a yellow solid (14.2 mg, 0.061 mmol, 61% yield). The crude product was obtained as a mixture of a/b = 4.2:1. The isolated product was an inseparable mixture of isomers; however, only the peaks for major isomer are reported.  3k: Following the general procedure described above with XI (1.35 mg, 0.005 mmol, 0.05 equiv) and tert-butyldimethyl(phenoxy)silane (208 mg, 1.0 mmol, 10.0 equiv) as the arene source, 3k was obtained as a white solid (25.1 mg, 0.071 mmol, 71% yield, a/b = 1:2). The isomer ratios were determined through 1 H-NMR. The isolated product was an inseparable mixture of isomers. All peaks observed in the 1 H-NMR and 13 C-NMR were assigned.

General procedure for the synthesis of authentic 3k:
In a microwave reaction tube equipped with a magnetic stir bar, phthalic anhydride (740 mg, 5 mmol, 1.0 equiv), acetic acid (10.0 mL) and aniline derivative (5.0 mmol, 1.0 equiv) were taken. The mixture was heated at 120 °C for 30 min under microwave irradiation. The reaction mixture was cooled to rt and treated with water. A white precipitate was observed, which was filtered, washed with water and dried in vacuo. To the crude solid, TBSCl (900 mg, 6 mmol), imidazole (816 mg, 12 mmol) and DMF (10 mL) were added. The resulting mixture was stirred at rt for 2 h. The reaction mixture was cooled to 0 °C and a solution of 1N HCl (20 mL) was slowly added. The aqueous phase was extracted with diethyl ether (3 × 10 mL), washed with brine (1 × 30 mL), dried over Na 2 SO 4 and concentrated under reduced pressure. Purification of the residue by flash column chromatography over silica gel afforded the desired product. 3k (ortho): The general procedure described above was followed with 2-amino phenol (5.0 mmol, 1.29 g) to obtain a white solid (882 mg, 51% yield  Recrystallization of 3l from CH 2 Cl 2 /hexane (1:9) mixture afforded diffraction quality crystals. The thermal ellipsoids of non-hydrogen atoms are shown at the 50% probability level. Calculated hydrogen atoms are omitted for clarity. The atoms are shown through following colour sequence: blue = nitrogen, red = oxygen, grey = carbon. OMe CN NPhth 3n: Following the general procedure described above with XI (1.35 mg, 0.005 mmol, 0.05 equiv) and 1,3-dimethoxybenzene (0.13 mL, 1.0 mmol, 10.0 equiv) as the arene source, 3n was obtained as a white solid (24.0 mg, 0.085 mmol, 85% yield, a/b = 1:9). The isomer ratios were determined through 1 H-NMR. The isolated product was an inseparable mixture of isomers, however, only the peaks for major isomer are reported.

F. Calculation of ∆G et by Rehm-Weller Equation:
The ∆G et (et: electron transfer) was calculated by the following equation: is the oxidation potential of the donor, E red (A) is the reduction potential of the acceptor, ∆E triplet is the triplet energy of the ketone and ∆E columbic is the term for columbic interaction in a particular solvent. The value of ∆E coloumbic is usually very small in polar solvents (~ 0.03 eV for CH 3 CN) and thus this parameter is not incorporated in the calculations. The calculated values are listed below:

G. UV-Visible Absorption Spectroscopy:
UV-Visible absorption spectra of ketone catalysts were measured in CH 3 CN (for Spectrochemical Analysis) on a Shimadzu UV-3510 spectrometer.

K. Quantum Yield Measurement:
The quantum yield was measured by standard ferrioxalate actinometry. 11 A 300W Xenon lamp (5% of light intensity, 365 ± 5 nm band pass filter high transmittance) was used as the light source. The

a) Measurement of light intensity at 365 nm
To determine the photon flux of the spectrophotometer, 2.0 mL of ferrioxalate solution was placed in a cuvette and irradiated for 90.0 seconds at 365 nm with an emission slit width at 10.0 nm. After irradiation, 0.35 mL of phenanthroline solution was added to the cuvette. To ensure complete coordination of ferrous ions with phenanthroline, the solution was kept for 1 h. The absorbance of the solution was measured at 510 nm. A non-irradiated (in dark) sample was also prepared and the absorbance at 510 nm was measured. Conversion was calculated using equation 1.

∆ 510 510 1
Where V is the total volume (0.00235 L) of the solution after addition of phenanthroline, ΔA is the difference in absorbance at 510 nm between irradiated and non-irradiated solutions, l is the path length (1.000 cm), and ε is the molar absorptivity at 510 nm (11,100 L mol -1 cm -1 ). The photon flux can be calculated using equation 2.

Determination of fraction of light absorbed at 365 nm for the ferrioxalate solution:
The absorbance of above ferrioxalate solution at 365 nm was measured to be > 3. The fraction of light absorbed (f) by this solution was calculated using equation 3.

Photoredox Ketone Catalysis for Direct C-H Imidation and Acyloxylation of Arenes, Ooi et al., Page S-21 b) Measurement of quantum yield
A screw-top cuvette was charged with the catalyst XI (10 mol%), 1a (0.24 mL, 2.0 mmol, 10.0 equiv), 2 (0.2 mmol, 80 mg, 1.0 equiv), CH 3 CN (2 mL, 0.1 M), and a small magnetic stir bar was also introduced. The cuvette was degassed with a nitrogen stream for 10 min. After degassing, the reaction mixture was stirred and irradiated with 150 W Xenon lamp (5% of light intensity, 365 nm ± 5 nm band pass filter) for 86400 s (24 h). After irradiation, the reaction mixture was evaporated. The reaction yield was determined through 1 H-NMR by using 1,3,5-trimethoxybenzene as internal standard. Essentially all the incident light (f > 0.999, vide infra) is absorbed by the catalyst under the conditions described above. The quantum yield is calculated as shown below: 1.54 10 5.004 10 86400 1 0.036 L. Crystallographic Structure Determination of 3l: The single crystal obtained by recrystallisation in CH 2 Cl 2 /hexane (1:9) at room temperature was mounted on MicroMesh. X-ray diffraction data was collected at 123 K on a Rigaku VariMax with a Pilatus diffractometer and a fine-focus sealed tube Mo/Kα radiation (λ = 0.71075 Å). An absorption correction was made using Crystal Clear. The structure was solved by direct methods and Fourier syntheses. The data was refined by full-matrix least squares on F 2 by using SHELXL-2014. 13 All non-hydrogen atoms were refined with anisotropic displacement parameters. The other hydrogen atoms were placed in a calculated positions and isotropic thermal parameters were refined. The crystallographic data are summarized in the table below and the ORTEP diagram is shown on page S-10.
Crystal data and structure refinement for 3l.

N. Synthesis and Characterization of Aryl-Acylperoxide:
The aryl-acylperoxides were prepared by following the modified literature procedure. 16 In a 100 mL round bottom flask equipped with magnetic stir bar, a solution of the acid chloride (7.3 mmol) in Et 2 O (3.0 mL) was cooled to 0 °C. H 2 O 2 (aq. 30% by wt., 0.5 mL) was added dropwise followed by the dropwise addition of an aqueous solution of NaOH (364.0 mg in 2.0 mL H 2 O) over 20 minutes. The reaction was quenched by adding a saturated aqueous solution of NaHCO 3 (15 mL). The resulting solid was filtered and the aqueous phase was extracted with Et 2 O (2 × 20 mL). The filtered solid was mixed with the organic phase, dried over anhydrous Na 2 SO 4 and concentrated under reduced pressure at low temperature to afford a white solid. Recrystallization from hexane yielded the aryl-acylperoxides as a white solid.

Effect of Oxygenating Agent
Considering our results for C-H imidation of arenes, we thought that the aryl-acylperoxides with electron-withdrawing groups would be suitable for the C-H acyloxylation of arenes. Among the several candidates examined in the reaction of benzene, pentafluorobenzoyl peroxide led to afford the acyloxylation product in the highest yield.

Effect of Light Intensity
During optimization of the reaction conditions, we observed that 365 nm light with high intensity caused the decomposition of 4. Therefore, we reasoned that decreasing the light intensity might be beneficial for improving the efficiency. After carefully conducting the C-H acyloxylation with different intensity of 365 nm light, we concluded that 325 W/m 2 was an optimum intensity.

Catalyst Optimization
A brief catalyst screening revealed that X was optimal and the product was obtained in 63% yield.

Effect of Solvent
The reaction yield greatly depended upon the solvents and the best result was obtained by using a 1:1 mixture of toluene and 1,2-dichloroethane. In a flame and vacuum dried reaction tube, 4 (84.4 mg, 0.2 mmol, 1.0 equiv) and X (5.0 mg, 0.02 mmol, 0.1 equiv) were taken. The reaction flask was degassed in vacuo and backfilled with argon. Then, CH 3 CN/DCE (2.0 mL, v/v = 1:1) and arene (2.0 mmol, 10.0 equiv) were added. The resulting solution was stirred at 25 °C under 365 nm irradiation (325 W/m 2 ) for 15 h. The reaction was quenched by adding a saturated aqueous solution of NaHCO 3 (5 mL). The aqueous phase was extracted with CH 2 Cl 2 (3 × 10 mL). The combined organic phase was dried over anhydrous Na 2 SO 4 and concentrated under reduced pressure. Purification of the residue by column chromatography over silica gel afforded 5.