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.

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

References and Notes

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Other achievements of trifluoromethylation reagents have been reported during the preparation of this manuscript, see:

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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.

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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.

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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.