Reactions of Metal Alkyl-Active Methylene Chelate Compounds with α,β-Unsaturated Carbonyl Compounds

The method of the preparation of zinc (or aluminum) alkyl-active methylene chelate compounds was studied. The chelate compounds were identified mainly by NMR, IR, and component analysis. Zinc alkyl-active methylene chelate compounds were found to cause a Michael-type addition reaction with α,β-unsaturated esters or nitriles. Aluminum alkyl-active methylene chelate compounds exhibited lower reactivities than the zinc chelate compounds toward α,β-unsaturated carbonyl compounds. Kinetic studies of the addition reaction revealed that the reaction proceeded according to a first-order rate law with respect to both the metal compound and the α,β-unsaturated carbonyl compound. The effects of substituents on the metal atom as well as on the chelate ring were also studied. The intercorrelation among the chemical shift of the methine proton of the chelate ring, σp of the subsituents and the reactivity of metal alkyl-active methylene chelate compounds suggested that the rate of the addition reaction was governed mainly by the stability of the chelate ring.