The Metal-Ion-Catalyzed Alcoholysis of β-Dicarbonyl Compounds

Abstract The alcoholysis of β-dicarbonyl compounds of the type CH3COCHRCOR′ is catalyzed by a variety of metal ions. In the presence of a large excess of β-diketone compared with metal ions, the rate is given by the expression: rate=kobsd[M2+][ROH]. The values of kobsd decrease with M2+ in the order Zn2+>Co2+>Ni2+>Cu2+. The reaction rate is remarkably affected by the substituents (R,R′), the kinds of alcohol and solvent used, the addition of a chelating agent, and also by the counter anion of the metal ion. The alcoholysis proceeds more slowly in CH3OD than in CH3OH by a factor of 1.4. These are interpreted in terms of a mechanism in which the β-dicarbonyl compound coordinated to a metal ion is attacked by the alcohol which is also coordinated to the metal ion to cleave the C2–C3 or C3–C4 bond of the dicarbonyl compound. A convenient method for the preparation of β,γ-unsaturated ketones and esters is provided by the alcoholysis of alkenyl substituted β-dicarbonyl compounds in the presence of zinc acetate.