Reactions of carbonyl compounds in basic solutions. Part 10. Methoxide-catalysed cyclisation of methyl 2-acylbenzoates and 8-acyl-1-naphthoates

Abstract

The detailed mechanism of the methoxide-catalysed rearrangement of both normal and pseudo methyl o-acylbenzoates and 8-acyl-1-naphthoates to form indane-1,3-diones and phenalene-1,3-diones, respectively, has been studied. Rate–acidity function correlations for the reactions in methanolic dimethyl sulphoxide give linear relations. The kinetic isotope effects have been observed with k_H/k_D equal to 0.7–0.9 and 5–7 for methyl o-acetylbenzoate and normal methyl 8-acetyl-1-naphthoate, respectively. The effect of substituents and ring–chain tautomerism on the rates has been considered. For the o-acylbenzoates the initial state is the ring-chain tautomeric equilibrium mixture and the rate-determining step is the intramolecular attack of the anion of the normal ester. For normal 8-acyl-1-naphthoates the rate-determining step is the ionisation of the normal esters; for the corresponding pseudo esters, the rate-determining step is the isomerisation of the psuedo to the normal ester.