Bromotrifluoromethane: A Useful Reagent for Hydrotrifluoromethylation of Alkenes and Alkynes

Abstract

Bromotrifluoromethane (CF₃Br) is a simple, inexpensive and abundant industrial material employed as a trifluoromethylating reagent. However, only limited strategies using CF₃Br as a fluorine source are reported. Herein, we describe a visible-light-induced hydrotrifluoromethylation of alkenes and alkynes with CF₃Br. The reaction proceeds under mild conditions with good functional group tolerance, providing a new route for the application of BrCF₃ in organic synthesis.

Key words

bromotrifluoromethane - hydrotrifluoromethylation - alkenes - alkynes - visible-light-induced

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• 15 Hydrotrifluoromethylation with CF₃Br;Typical Procedure To a 25 mL Schlenk tube were added fac-Ir(ppy)₃ (0.5 mol%) and K₂CO₃ (126 mg, 0.9 mmol, 3.0 equiv). The mixture was then evacuated and backfilled with argon (3 times). The mixture was evacuated again and backfilled with CF₃Br (1 atm), followed by the addition of alkene 1b (0.3 mmol, 1.0 equiv) and anhydrous THF (1.5 mL). The tube was screw-capped and irradiated with a blue LED (12 W) at room temperature. After stirring for 30 h, the reaction mixture was diluted with EtOAc (2 mL) and filtered through a pad of Celite. The filtrate was concentrated, and the residue was purified by silica gel chromatography (hexane/EtOAc, 20:1) to give product 3b (50 mg, 60% yield) as a colorless oil.
• 16 5,5,5-Trifluoropentyl 4-Methoxybenzoate (3b) ¹H NMR (400 MHz, CDCl₃): δ = 7.98 (d, J = 8.3 Hz, 2 H), 6.91 (d, J = 8.4 Hz, 2 H), 4.29 (t, J = 5.9 Hz, 2 H), 3.83 (s, 3 H), 2.23–2.06 (m, 2 H), 1.86–1.76 (m, 2 H), 1.76–1.65 (m, 2 H); ¹³C NMR (101 MHz, CDCl₃): δ = 166.2, 163.4, 131.5, 127.0 (q, J = 276.4 Hz), 122.5, 113.6, 63.8, 55.4, 33.4 (q, J = 28.7 Hz), 27.9, 18.8 (q, J = 3.0 Hz); ¹⁹F NMR (376 MHz, CDCl₃): δ = –66.5 (t, J = 10.8 Hz, 3 F); MS (EI): m/z (%) = 276 [M]⁺, 135 (100); HRMS (EI): m/z [M]⁺ calcd for C₁₃H₁₅O₃F₃: 276.0973; found: 276.0978.