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Synlett 2010(2): 261-265  
DOI: 10.1055/s-0029-1218571
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Fe/CuBr2-Catalyzed Benzylation of Arenes and Thiophenes with Benzyl Alcohols

Chengyi Zhang, Xinqin Gao*, Jianghua Zhang, Xiaojun Peng
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, P. R. of China
Fax: +86(411)39893800; e-Mail: gaoxq@dlut.edu.cn;
Further Information

Publication History

Received 9 September 2009
Publication Date:
11 December 2009 (online)

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Abstract

An inexpensive and relatively nontoxic Fe/CuBr2-catalyzed benzylation of arenes and thiophenes with benzyl alcohols has been developed. The reaction can be carried out under mild conditions to afford diarylmethane derivatives in high yields and good ­selectivity.

Key words

benzylation - benzyl alcohols - iron - cupric bromide - ­diarylmethanes

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Typical Procedure for the Benzylation of Arenes
Benzyl alcohol (1 mmol), arene (1 mL), CuBr2 (10 mol%,
0.1 mmol), reductive Fe powder (20 mol%, 0.2 mmol), and DCE (5 mL) were put into a flask fitted with a pressure-equalized addition funnel (containing a cotton plug and 1 g of CaH2 and acting as a Soxhlet extractor) surmounted by a reflux condenser. After stirring for 20 h at 84 ˚C, the reaction was quenched with H2O. The stirring bar was removed and washed with CH2Cl2. The aqueous phase was extracted three times with CH2Cl2. The combined organic layers were dried over MgSO4, and the solvents were evaporated. The product was purified by silica gel column chromatography (200-300 mesh; n-hexane-EtOAc, 50:1).
2-Benzyl-3,4-dibromothiophene (3u) ¹H NMR (400 MHz, CDCl3, 25 ˚C): δ = 7.34-7.28 (m, 2 H, Ar), 7.25-7.21 (m, 3 H, Ar), 7.17 (s, 1 H, Ar), 4.16 (s, 2 H, ArCH2). HRMS: m/z calcd for C11H8SBr2: 329.8713; found: 329.8714.
General Procedure for the Benzylation of Thiophene Benzyl alcohol (1 mmol), thiophene (1 mL), CuBr2 (10 mol%, 0.1 mmol), reductive Fe powder (20 mol%, 0.2 mmol), and DCE (5 mL) were put into a flask fitted with a pressure-equalized addition funnel (containing a cotton plug and 1 g of CaH2 and acting as a Soxhlet extractor) sur-mounted by a reflux condenser. After stirring for 20 h at 84 ˚C, the reaction was quenched with H2O. The stirring bar was removed and washed with CH2Cl2. The aqueous phase was extracted three times with CH2Cl2. The combined organic layers were dried over MgSO4, and the solvents were evaporated. The product was purified by silica gel column chromatography (200-300 mesh; n-hexane-EtOAc, 50:1).
2-Furyl-2-thienylmethane (6g) ¹H NMR (400 MHz, CDCl3, 25 ˚C): δ = 7.33 (s 1 H, Ar), 7.15 (d J = 4.8 Hz, 1 H, Ar), 6.93 (dt J = 2.8, 5.2 Hz, 1 H, Ar), 6.86 (d, J = 2.8 Hz, 1 H, Ar), 6.29 (s, 1 H, Ar), 6.08 (d, J = 2.8 Hz, 1 H, Ar), 4.15 (s, 2 H, ArCH2). MS (EI): m/z = 164 [M+].