"In addition, phase separation is easier because most organic compounds are lipophilic and can be easily separated from the aqueous phase. Assumed that the heterogeneous catalysts exhibit high catalytic activity in water, the catalysis would represent an almost ideal synthetic process (Arcadi et al., 2003). Water is compatible with most of the known palladium-catalyzed reactions (Belet-skaya and Cheprakov, 2002). "
[Show abstract][Hide abstract] ABSTRACT: An efficient Suzuki cross-coupling reaction using a variety of aryl halides in neat water was developed. The Pd-catalyzed reaction between aryl bromides or chlorides and phenyl bo-ronic acids was compatible with various functional groups and affords biphenyls in good to excellent yields without requirement of organic cosolvents. The air stability and solubility in water of the palladium-phosphinous acid complexes were considered to facilitate operation of the coupling reaction and product isolation. The reaction conditions including Pd catalyst selection, temperature, base and catalyst recoverability were also investigated.
[Show abstract][Hide abstract] ABSTRACT: [reaction: see text] Sterically demanding, sulfonated arylphosphines TXPTS and TMAPTS have been applied to the aqueous-phase Heck and Suzuki coupling of aryl bromides. TXPTS provides good yields of Heck coupling products from aryl bromides at 80 degrees C, while both TMAPTS and TPPTS gave significantly less active catalysts. TXPTS is the first ligand to promote the aqueous-phase Heck coupling under such mild conditions. Both TXPTS and TMAPTS provide active catalysts for Suzuki couplings of aryl bromides at 50 degrees C.
[Show abstract][Hide abstract] ABSTRACT: Di(2-pyridyl)methylamine-based palladium dichloride complexes 4 are versatile catalysts for different types of cross-coupling reactions in water or aqueous solvents under aerobic conditions. The Suzuki–Miyaura reaction of arylboronic acids can be performed with bromoarenes under water reflux using K2CO3 as base or at room temperature or 60 °C in aqueous methanol using KOH as base. For aryl chlorides the corresponding cross-couplings with arylboronic acids can be carried out in refluxing water with K2CO3 as base and TBAB as additive to provide biaryls and heterobiaryls. Arylboronic acids react with benzylic chlorides and allylic substrates such as chlorides, acetates or carbonates also in refluxing water with K2CO3 as base or at room temperature in aqueous acetone and KOH as base, to give diarylmethanes and arylpropenes. Trimethylboroxine and alkylboronic acids are coupled with bromo- and chloroarenes under water at reflux with K2CO3 as base and TBAB as additive to furnish methyl- and butylarenes. These cross-couplings have also been performed in shorter times under microwave irradiation. Several important intermediates such as, 4′-methylbiphenyl-2-carbonitrile, 4-biphenylacetic acid, 3-(3-methylphenyl)benzoic acid, 4,5-diphenyl-2-methyl-3(2H)pyridazinone and 2-(4′-fluorobenzyl)thiophene have been prepared under aqueous and aerobic conditions in good yields.
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