Palladium-catalyzed Heck arylation of 5-hexen-2-one in ionic liquid: A novel approach to arylated γ,δ-unsaturated ketones

γ-Arylated γ,δ-unsaturated ketones have been prepared in good to excellent yields via the Pd-catalyzed Heck arylation of an electron-rich olefin, 5-hexen-2-one (1), with aryl bromides (2a–2l) in the ionic liquid [bmim][BF4]. The reaction is highly regioselective, leading predominantly to branched, γ-arylated products with Pd-DPPP [DPPP = 1,3-bis(diphenylphosphino)propane] catalysis. However, the choice of ligand is found to be crucial for regiocontrol; a change of ligand from DPPP to 1,1′-bis(diphenylphosphino)ferrocene (DPPF) affords predominantly the (E)-type, δ-arylated γ,δ-unsaturated ketones. The method is simple, effective, and applicable to the coupling of both electron-rich and electron-deficient aryl bromides with no need for any halide scavengers.

Graphical abstractControlled regioselectivity: Depending on the ligand used, the Heck arylation in ionic liquid affords the γ-arylated γ,δ-unsaturated ketones or the (E)-type δ-arylated γ,δ-unsaturated ketones with high regioselectivity with no need for costly or toxic halide scavengers.Figure optionsDownload full-size imageDownload as PowerPoint slide