ION-PAIRING AND REACTIVITY OF BETA-KETOENOLATES

Relationships between structure and reactivity for alkali salts of the following symmetrical $-diketones in dimethyl sulfoxide solution are considered: dibenzoylmethane; dipivaloylmethane; 3-methylpentane-2,4-dione; 2-methyldimedone; dimethyl methylmalonate and isopropylidene methylmalonate (methyl Meldrum's Acid). Lithium, sodium, potassium, cesium and tetrabutylammonium salts were compared in several cases. The stabilities and structures of the ion-pairs were studied by conductance, nmr, far infrared and by the rates and heats of reaction with methyl iodide. The results, for the most part, are consistent with a simple two- state equilibrium and imply that the cyclic enolate anions are more stable than their acylic analogues both in terms of dissociation from the ion pair and also in terms of their reactivities to proton transfer and alkylation. © 1979, Walter de Gruyter. All rights reserved.