Electrophotocatalytic Undirected C−H Trifluoromethylations of (Het)Arenes

Abstract Electrophotochemistry has enabled arene C−H trifluoromethylation with the Langlois reagent CF3SO2Na under mild reaction conditions. The merger of electrosynthesis and photoredox catalysis provided a chemical oxidant‐free approach for the generation of the CF3 radical. The electrophotochemistry was carried out in an operationally simple manner, setting the stage for challenging C−H trifluoromethylations of unactivated arenes and heteroarenes. The robust nature of the electrophotochemical manifold was reflected by a wide scope, including electron‐rich and electron‐deficient benzenes, as well as naturally occurring heteroarenes. Electrophotochemical C−H trifluoromethylation was further achieved in flow with a modular electro‐flow‐cell equipped with an in‐operando monitoring unit for on‐line flow‐NMR spectroscopy, providing support for the single electron transfer processes.


General Procedure B for the Electrophotochemical C-H Trifluoromethylation
The electrophotocatalysis was carried out in an undivided cell with a GF anode (10 mm × 15 mm × 6 mm) and a Pt cathode (10 mm × 15 mm × 0.25 mm). Substrate 1 or 4 (0.25 mmol, 1.0 equiv), CF 3  Characterization Data of Products.

2-Butyl-5-(trifluoromethyl)thiophene (5h)
The ratio of two mono-substituted products was determined to be 10:1 by 1 H-NMR analysis of the crude reaction mixture. The general procedure A was followed using 4h (
Purification by column chromatography on silica gel (n-hexane/EtOAc S-14

S-16
The ratio of two mono-substituted products was determined to be 20:1 by 1

On-Line NMR Monitoring in Flow
The

Estimation of quantum yield
The quantum yield Φ is defined as the ratio between the number or rate of desired photochemical transformations and the number or rate of absorbed photons. In our reaction, the reaction velocity v r is driven by electric current, which for a 2-electron process at ideally 100% faradaic yield corresponds to a maximum value of: The photon flux was determined using the well-established Hatchard-Parker actinometer. [7] Two solutions were prepared for the quantification of Fe(II) produced by photochemical decomposition of potassium ferrioxalate: were added and the solution was topped with distilled water to a total volume of 25 mL.
Phenanthroline buffer P: 150 mg (0.83 mmol) phenanthroline and 2.050 g (25 mmol) NaOAc were dissolved in approx. 40 mL of distilled water. Subsequently, 0.50 mLH 2 SO 4 (9 mmol) were added and the solution was topped with distilled water to a total volume of 50 mL.
The measurement was performed in the typical reaction setup: A Schlenk-tube, equipped with a magnetic stirring bar and a rubber septum with electrode inlets was charged with 4 mL of solution F. The sample was irradiated with blue light for 20 s (2 × Kessil A360N).
Subsequently, a 1/40 aliquot (100 µL) was taken and dissolved in 10 mL of solution P to obtain complex solution C 1 . This procedure was repeated with a non-irradiated sample to obtain complex solution C 0 .