Indium-Catalyzed Cross-Coupling Reactions between (alpha),(beta)-Unsaturated Carbonyl Compounds and Aromatic Aldehydes

Cross-coupling reactions between (alpha),(beta)-unsaturated carbonyl compounds and aromatic aldehydes have been achieved in tetrahydrofuran (THF) at 25 °C under N2 using a catalytic amount of InCl3 (0.05 molar amount to the substrate) in the presence of both chlorotrimethylsilane (TMSCl) and aluminum foil (Al). These reactions provide the corresponding (beta),(gamma)-unsaturated ketones in moderate yields, together with pinacol-coupling products of aldehydes as side products. Chlorides other than TMSCl and AlCl3, such as LiCl, CaCl2, MgCl2, and SOCl2, are not effective at all. Without either TMSCl or Al, no reaction proceeds even in the presence of the catalyst.