Microwave-Assisted Copper-Catalyzed Heck Reaction in PEG Solvent

Abstract

A catalytic system made of a copper salt, potassium carbonate and PEG 3400 was developed to perform a Heck arylation under microwave activation. Copper iodide gave the best results in a short reaction time (30 min) and various substituted tert-butyl cinnamates could be synthesized. Better results were usually obtained after recycling the catalyst/solvent system.

Key words

Heck reaction - microwave - arylation - copper - poly(ethylene glycol)

References and Notes

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33

Copper-Catalyzed Heck Reaction of Phenyl Iodide with tert -Butyl Acrylate. To a mixture of CuI (1.9 mg, 0.01 mmol, 0.1 equiv), finely powdered K₂CO₃ (41 mg, 0.3 mmol, 3 equiv) and PEG 3400-OH (250 mg) were added phenyl iodide (20 mg, 0.1 mmol, 1 equiv) and tert-butyl acrylate (64 mg, 0.5 mmol, 5 equiv). The resulting mixture was heated by microwave irradiation at 150 °C (initial power 300W) for 30 min. After cooling, the reaction mixture was solubilized in CH₂Cl₂ and precipitated in Et₂O. Filtration and evaporation afforded tert-butyl cinnamate (2) in 59% yield (measured by ¹H NMR using CH₂Br₂ as internal standard). The precipitate was reused in a similar reaction with finely powdered K₂CO₃ (41 mg, 0.3 mmol, 3 equiv), phenyl iodide (20 mg, 0.1 mmol, 1 equiv) and tert-butyl acrylate (64 mg, 0.5 mmol, 5 equiv) to give tert-butyl cinnamate (2) in 100% yield (measured by ¹H NMR using CH₂Br₂ as internal standard).