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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13
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.
14
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 2 SO4 , 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 CH2 Cl2 . The products were obtained after evaporation of the extract. The arylmolononitriles were further purified by recrystallization [petroleum ether 2 Cl2 , 6:1]. The products of coupling were identified by means of 1 H NMR and mp, which are in agreement with literature data.
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