A Ligand-Free Copper-Catalyzed Decarboxylative Trifluoromethylation of Aryliodides with Sodium Trifluoroacetate Using Ag₂O as a Promoter

Abstract

A practical and ligand-free Cu-catalyzed decarboxylative trifluoromethylation of aryl iodides with sodium trifluoroacetate using Ag₂O as a promoter was reported. A variety of trifluoromethyl-substituted aromatics are synthesized in moderate to excellent yields and with wide functional-group tolerance under relatively mild reaction conditions.

Key words

copper-catalyzed - trifluoromethylation - decarboxylative - silver oxide - cross-coupling

References and Notes

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23

General Procedure for the Preparation of Aryl Trifluoromethylation Derivatives
Method A for the Electron-Deficient Aryl Iodides (Compounds 1a-e,l-n,p-r)
A flame-dried Schlenk test tube with a magnetic stirring bar was charged with Cu (9.6 mg, 0.15 mmol), Ag₂O (34.8 mg, 0.15 mmol), aromatic halides (0.5 mmol), sodium trifluoro-acetate (272 mg, 2.0 mmol), and DMF (2 mL) under argon.
Method B for Electron-Rich Aryl Iodides (Compounds 1f-k,o)
A flame-dried Schlenk test tube with a magnetic stirring bar was charged with Cu (12.8 mg, 0.2 mmol), Ag₂O (46.4 mg, 0.2 mmol), aromatic halides (0.5 mmol), sodium trifluoro-acetate (272 mg, 2.0 mmol), and DMF (2 mL) under argon. After reacting at 130 ˚C for 15 h, the reaction mixture was cooled to ambient temperature, and extracted with EtOAc (3 × 20 mL). The combined organic layers were dried over anhyd Na₂SO₄ and concentrated under vacuum. The residue was purified by column chromatography on silica gel with an eluent of PE and EtOAc.

24

After the reaction mixture was cooled to r.t., the yields of compounds 2a-f,h,i,l were determined by ^¹9F NMR with CF₃CH₂OH (0.5 mmol, 36 µL) as internal standard due to their low bp; compounds 2a,d,h are also commercial available.

25

1,3-Dimethoxy-5-(trifluoromethyl)benzene (2g)
Following the general procedure (method B) NMR yield: 82%. ^¹H NMR (400 MHz, CDCl₃): δ = 6.74 (2 H, d, J = 1.6 Hz), 6.59 (1 H, t, J = 2.0 Hz), 3.81 (6 H, s). ^¹³C NMR (100 MHz, CDCl₃): δ = 161.2, 132.6 (q, J = 30 Hz), 124.1 (q, J = 270 Hz), 103.8, 103.4, 55.7. ^¹9F NMR (376 MHz, CDCl₃): δ = -63.4 (3 F, s). HRMS (GC-TOF MS, EI): m/z calcd for C₉H₉O₂F₃: 206.0555; found: 206.0546.