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Synlett 2003(11): 1716-1718
DOI: 10.1055/s-2003-41429
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© Georg Thieme Verlag Stuttgart · New York

A Convenient and Efficient Palladium-Catalyzed System for Cross-Coupling of Aryl Bromides with Active Methylene Compounds

Chengwei Gao, Xiaochun Tao, Yanlong Qian, Jiling Huang*
Laboratory of Organometallic Chemistry, East China University of Science and Technology, Shanghai 200237, P. R. China
e-Mail: qianling@online.sh.cn;
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Publication History

Received 3 June 2003
Publication Date:
22 September 2003 (online)

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Abstract

A simply catalytic system containing palladium-phosphine complex, generated in situ from PdCl2/tert-phosphino ligand in pyridine, has been systematically studied in the cross-coupling of bromobenzene with malononitrile or ethyl cyanoacetate anion. The effect of molar ratio of phosphine ligand to PdCl2 on the activity of the coupling was also discussed. It is found that the catalytic system has highly catalytic activity to produce aryl malononitriles and cyanoacetates in considerable yields (67-90%) when the substituted aryl bromides were used as substrates.

Key word

palladium catalysis - cross-coupling - arylmalononitrile - arylcyanoacetate - aryl bromide

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Preparation of the catalyst in pyridine: Triphenylphosphine (0.06 mmol) and palladium chloride (0.02 mmol) were mixed in a predried Schlenk tube under dry argon. Then 1 mL of dry pyridine was added and the mixture was stirred at 60 °C for 15 min.

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General procedure for the cross-coupling of aryl bromides with active methylene compounds: Under an Ar atmosphere to a predried Schlenk tube with 5 mL of dry pyridine was added a mixture of NaH (5.4 mmol) and malononitrile or ethyl cyanoacetate (2.5 mmol), respectively. Following the catalyst (PdCl2/Ligand) [13] prepared as described above was injected, and the mixture was stirred at ambient temperature for 5min. After addition of an aryl bromide (2 mmol), the mixture was heated at
85 °C for an appropriate time (10-12 h). The progress of the reaction was monitored by TLC. After removal of the solvent by distillation in vacuum, the residue was neutralized with diluted hydrochloric acid (10 mL), and the product was extracted with 15 mL × 3 diethylether, washed with 2 × 10 mL of brine, dried over Na2SO4, filtered and concentrated. The residue from the ether extract was purified by TLC (silica gel GF254, 20 × 20 cm) using a developing solution of petroleum ether (60-90 °C)/ethyl acetate (6:1 for arylmolononitriles or 10:1 for aryl ethyl cyanoacetates), and the fractions containing the products were collected and extracted with CH2Cl2. The products were obtained after evaporation of the extract. The arylmolononitriles were further purified by recrystallization [petroleum ether
(60-90 °C)/CH2Cl2, 6:1]. The products of coupling were identified by means of 1H NMR and mp, which are in agreement with literature data. [5-11]