Electroorganic reactions. Part 37. The stereochemistry and mechanism of the cathodic hydrogenation of methyl 4-tert-butylcyclohex-1-enecarboxylate

Abstract

Methyl 4-tert-butylcyclohex-1-enecarboxylate is hydrogenated at a mercury cathode, in the presence of proton donors, in a smooth 2 F mol–1 process. The proportions of cis and trans isomers in the product (methyl 4-tert-butylcyclohexanecarboxylate) are a function of reaction conditions and detailed consideration shows that the reaction is under kinetic control. Protonation of the first-formed radical anion is probably at C-1, with little stereoselectivity. The results of base- and radical-induced epimerizations of 1,4-disubstituted cyclohexanes were used to establish the likely outcome of thermodynamic control. These results are in impressive agreement with calculations based on substituent group conformational preferences.