Suzuki–Miyaura and Related Cross‐Couplings in Aqueous Solvents Catalyzed by Di(2‐pyridyl)methylamine‐Palladium Dichloride Complexes

Abstract

AbstractDi(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.