A paradoxical case of Dieckmann cyclisation

Abstract

The isomerisation of ethyl 1-ethoxycarbonyl-2-oxocyclopentylacetate to ethyl 3-ethoxycarbonyl-2-oxocyclopentylacetate has been shown to proceed via diethyl β-ethoxycarbonylpimelate. The mechanism proposed by Chakravarti1 is untenable. A mechanism based on the equilibrium nature of the reaction has been formulated to explain the formation of ethyl 3-oxocyclohexane-1: 2-dicarboxylate or ethyl 3-ethoxycarbonyl-2-oxocyclopentyl-acetate, as the major product, from diethyl β-ethoxycarbonylpimelate under different experimental conditions of Dieckmann cyclisation. Other mechanisms have also been discussed.