doi:10.1016/j.ultsonch.2004.05.011 
Copyright © 2004 Elsevier B.V. All rights reserved.
Ultrasound effect on Suzuki reactions. 1. Synthesis of unsymmetrical biaryls
Viera Poláčková, Martin Hut’ka and Štefan Toma
, 
Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská dolina CH-2, SK-842 15 Bratislava, Slovak Republic
Received 27 February 2004;
accepted 10 May 2004.
Available online 29 July 2004.
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Abstract
Ultrasound effect on the Pd(0) catalysed reaction of arylboronic acid with halobenzenes was investigated. The effect of catalyst, base as well as solvent was tested. Heterogenous reaction of iodoarenes with different arylboronic acids, catalysed by Pd/C and KF as the base in methanol:water mixture resulted in good yields of cross-coupling products. Reaction time of sonochemical reaction was 1 h, while 4 h of reflux was necessary to achieve comparable results. Bromobenzenes gave best results using aqueous solution of PdCl2 as the catalyst, potassium carbonate as the base in toluene:water two phase system using TEBA (benzyltriethylammonium chloride) as PT catalyst. Chlorobenzenes gave just feeble yields of cross-coupling products.
Keywords: Biaryls; Arylboronic acid; Cross-coupling; Suzuki reaction; Sonochemical activation; Ultrasound
Table 1.
Effect of catalysts, bases and solvents on the reaction of iodobenzene with 4-methoxyphenylboronic acids
DMA (N, N-dimethylacetamide).
a One mmol iodobenzene, 1.1 mmol of 4-methoxyphenylboronic acid, 2 mmol base, 10 mol% catalyst, 1 h sonication.
b Six mmol of base.
c Nine mmol of base.
d Silent reaction, 1 h, 35 °C.
e Silent reaction, 4 h reflux.
Table 2.
Ultrasound promoted Suzuki coupling of iodoarenes and arylboronic acids
a One mmol aryliodide, 1.1 mmol of arylboronic acids, 9 mmol base, 15 mol% catalyst, 1 h sonication.
b Thirty minutes sonication.
Table 3.
Results of catalysts, bases and solvents effects on the sonochemical Suzuki coupling of 4-methoxyboronic acid with bromobenzene
Reaction conditions: 0.5 mmol of both reactants, 5 mol% of the catalyst, 1.5 mmol of the base, 1 mol% of TEBA and 1 h sonication. Isolated yield of the products are given.
a Without TEBA.
b 4-methoxyphenol.
c Stirred without US.
Table 4.
Results of sonochemical Suzuki reaction of 4-methoxyphenyboronic acids with substituted bromobenzenes
Reaction conditions: 0.5 mmol of both reactants, 5 mol% of the catalyst, 1.5 mmol of the base, 1 mol% of TEBA and 1 h sonication. Isolated yield of the products are given.
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