Catalysis of a decarboxylation by a crown ether

Abstract

The decarboxylation of sodium 3-(fluoren-9ylidene) -2-phenylacrylate in tetrahydrofuran is greatly accelerated (> lo6) by addition of dibenzo-18-crown-6ether and is very sensitive to the solvent, pointing to an important r61e for ion-pairing and H-bonding.WE have observed a striking catalytic effect both of added dibenzo-18-crom-6-ether and of solvent upon the decarboxylation of the sodium salt (2). Both (1) and the salt (2) lose CO, readily to produce initially the delocalized carbanion. The rate of this spontaneous reaction is greatly enhanced

Crown-cation complex effects. 8. Reactions of crown ether activated tert-butoxide ion

“…For example, the basic oxidation of fluorene to fluorenone25 in the presence of crown-activated tert-butoxide is rapid at room temperature (see eq 8). This (8) reaction occurs readily under phase-transfer conditions using cryptate-complexed hydroxide,253 18-crown-6-complexed hydroxide,25b or quaternary ammonium hydroxides.250 A mole of water is produced in this reaction for each mole of hydrocarbon oxidized to ketone. Water is, in turn, deprotonated by excess tert-butoxide and Haller-Bauer cleavage26 of the ketone ensues.…”

Crown ethers. A new aid to synthesis and to elucidation of reaction mechanisms

“…Macroheterobicycles and macrocyclic polyethers have likewise been used to increase the reactivity of "living centers" in anionic polymerization of alkenes and to promote such reactions in solvents of low dielectric constant (18). Alkylation reactions of diethylmalonate anions (15), dehydrohalogenations of d-halost.yrenes (16) (effected by KF in dipolar aprotic solvents) and decarboxylation of sodium carboxylates have also been catalyzed in this manner (17). Elucidation of Reaction Mechanisms Since 1970, crown ethers have increasingly been used to clarify the role of ion pairs in organic reaction mechanisms (70) and it is perhaps in this controversial area of chemistry that they may have greatest impact.…”