Aromatic Amination of Aryl Bromides Catalysed by Copper/β-Diketone Catalysts: The Effect of Concentration

Abstract

CuCl ligated with β-diketones were found to be good catalysts for the amination of aryl bromides. Crucial is the concentration of the substrates: at 5 M the rate and selectivity improves substantially. In addition, K₂CO₃ can be used as base instead of expensive Cs₂CO₃. Primary and secondary amines, heterocycles and anilines could be arylated in good yields.

Key words

amination - copper - halide - diketones - concentration

References and Notes

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20

We presume that either the secondary or the tertiary amine is the reductant.

23

Experimental Procedure.
A 50-mL thermostated reactor fitted with overhead stirrer (H.E.L auto-MATE) was charged with K₂CO₃ (7.26 g, 52.5 mmol), CuCl (0.25 g, 2.5 mmol) and 10 mL of NMP. The reactor was flushed with N₂ and stirring was started at 500 rpm. After addition of 50 mmol of aryl bromide, 60 mmol of amine and 6.25 mmol of diketone ligand the mixture was heated to 130 °C under N₂ and stirred for 16 h (or longer for reluctant substrates). In screening experiments a sample of 100-200 mg was taken after this period, which was diluted with 10 mL of EtOAc and filtered over a syringe filter. Analysis was by GC [HP5 column (30 m, id 0.32 mm, 0.25 µm film), 70-270 °C min in 10 min, 2 min at 270 °C] using dihexyl ether as internal standard. For preparative runs the reaction mixture was partitioned between CH₂Cl₂ and 1 N aq NaHCO₃. The organic phase was washed several times with 1 N aq NaHCO₃ to remove NMP, dried and the solvent was removed on the rotavap. The residue was purified by flash chromatography on silica (heptane-EtOAc 15:5).