Electro-organic reactions. Part VI. Stereoselective cathodic reduction of unhindered cyclic ketones

Abstract

The cathodic reduction to alcohol of the conformationally rigid ketones 4-t-butylcyclohexanone, dihydroisophorone, trans-decalin-2-one, and trans-4a-methyldecalin-2-one has been investigated with particular reference to factors influencing the ratio of axial : equatorial alcohol. The parameters which have been varied include cathode material, solvent, proton donor, cathode potential, current density, and supporting electrolyte. The highest stereoselectivity in favour of the axial alcohols (kinetic control) is obtained using small or doubly charged electrolyte cations in ethanol. From 4-t-butylcyclohexanone the corresponding cis-alcohol is thereby obtained in 98% purity and 84% current efficiency. The control of stereochemistry is explained in terms of ion-pairing of key carbanionic intermediates.