Trifluoromethylation Reactions with Potassium Trifluoromethanesulfinate under Electrochemical Oxidation

Abstract

The electrochemical oxidation of potassium trifluoromethanesulfinate (CF₃SO₂K) in the presence of electron-rich aromatics and alkenes provides the corresponding trifluoromethylated products.

Key words

trifluoromethylation - potassium trifluoromethanesulfinate - electrolysis - fluorinated compounds - trifluoromethylated alkanes and alkenes - trifluoromethylated aromatics

References

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10

A representative preparative-scale electrolysis for the synthesis of 5/6 is described as follows: A solution of CF₃SO₂K 1 (0.38g, 2.2 mmol) and NEt₄ClO₄ (2.87g, 12.5 mmol) in anhyd DMF (50 mL) containing 2 (1.53g, 11 mmol) was oxidized at 1.15V vs SCE in a three compartments cell, under positive nitrogen atmosphere, until the starting material was almost consumed (as checked by cyclic voltammetry, 2 F/mol). A circular platinum gauze (5 cm × 5 cm) was used as the anode which was separated from the cathodic solution (DMF-0.25 M NEt₄ClO₄ with platinum as cathode) with a glass frit of porosity 4. The yellowish solution was hydrolyzed with brine (150 mL), and extracted with Et₂O (3 × 100 mL). The combined organic solutions were washed with brine (3 × 100 mL), H₂O (3 × 100 mL) and dried over MgSO₄. Evaporation to dryness left a crude material which was directly analyzed by ¹⁹F NMR with a known concentration of PhOCF₃ (δ_F -58.3 ppm/CFCl₃) as internal standard. ¹⁹ F NMR (CDCl₃-CFCl₃): 1,3-dimethoxy-2-trifluoromethyl benzene 5, δ_F -54.26 (s, 3 F); 1,3-dimethoxy-4-trifluoromethyl benzene 6, δ_F -60.69 (s, 3 F).