Synthesis of aromatic ketones by Suzuki-Miyaura cross-coupling of acyl chlorides with boronic acids mediated by palladium catalysts deposited over donor-functionalized silica gel
Abstrakt
Immobilized palladium catalysts prepared by deposition of palladium(II) acetate over silica gel functionalized with Si(CH2)(3)NHCH2Y donor groups (Y= SMe (1), NMe2 (2), PPh2 (3)) efficiently mediate cross-coupling of benzoyl chloride with benzeneboronic acid and its derivatives possessing electron-donating substituents. The presence of electron-withdrawing groups at the benzene ring decreases the yield of the coupling product while aliphatic acyl chlorides such as PhCH2CH2COCl and t-BuCoCl provide the coupling products in only poor yields.
The course of the coupling reaction is very sensitive to the reaction conditions, the best results being achieved with potassium carbonate sesquihydrate as the base in dry toluene. The catalysts, which serve as the source of active metal, gradually loose their activity due to metal leaching and, mainly, decomposition of the solid support presumably by the action of the strong base present in the reaction system.