Visible-Light-Induced Stoichiometric Coupling of Alkylarenes and Trifluoromethyl Ketones

Qiao-Lin Wang, Huawen Huang*, Mengqi Zhu, Tianci Xu, Guojiang Mao and Guo-Jun Deng*

*College of Chemistry, Xiangtan University, Xiangtan 411105, P. R. China, Email: hwhuangxtu.edu.cn, gjdengxtu.edu.cn

Q.-L. Wang, H. Huang, M. Zhu, T. Xu, G. Mao, G.-J. Deng, Org. Lett., 2023, 25, 3800-3805.

DOI: 10.1021/acs.orglett.3c01307

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Abstract

A visible-light induced direct C(sp³)-H functionalization of alkylarenes with trifluoromethyl ketones provides valuable benzyl-substituted trifluoromethyl alcohols in a stoichiometric manner. With a bromine radical as the hydrogen atom transfer reagent, primary, secondary, and tertiary benzyl C-H bonds are suitable coupling partners.

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proposed mechanism

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Reaction Setup

A commercially available blue LED (35W, HIPAR30, luminous flux is not less than 3200 lm) was purchased from Shenzhen Jing Feng Times Lighting Technology Co., Ltd as the reaction light source. All irradiation reactions were carried out in borosilicate glass vessel. The distance from the light source to the irradiation vessel is around 4-5 cm.

Typical experimental procedure for the couplings

To a Schlenk tube was added trifluoromethyl ketone (0.2 mmol), alkylarene (0.4 mmol, 2.0 eqiuv), photocatalyst (0.004 mmol, 2 mol%), LiBr (50 mol%), 4Å MS (120 mg), acetone (4 mL). Then the mixture was stirred at room temperature in argon atmosphere (1 atm) under 35 W blue LED light for 48 h until complete consumption of starting material as monitored by TLC and GC-MS analysis. After the reaction was finished, the reaction mixture was washed with brine. The aqueous phase was re-extracted with EtOAc (3×10 mL). The combined organic extracts were dried over Na₂SO₄ and concentrated in vacuum. The residue was purified by silica gel flash column chromatography (hexane/ethyl acetate = 50 : 1 to 5 : 1) to afford the desired products.

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Key Words

alcohols, trifluoromethyl carbinols, photochemistry

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ID: J54-Y2023