Mechanism of the Liquid-Phase Catalytic Hydrogenolysis on Palladium/Carbon of Cyclohexene Epoxides

Article abstract of DOI:10.1021/jo01309a014

Heterogeneous catalytic hydrogenolysis of cyclohexene epoxides on 10percent Pd/C was studied in different solvents. The principal products were found to be alcohols, formed by cleavage of one epoxide C-O bond. In addition, simultaneous cleavage of both C-O bonds gave hydrocarbons, and isomerization on the catalyst gave ketones as byproducts. The deuterolysis of cis- and trans-tert-butylcyclohexene epoxides and kinetic studies with cyclohexene epoxides carrying an axial methyl group in position 3 or 5 showed that hydrogenolysis gives preferentially axial alcohols and trans hydrogen addition, after a "roll over" on the catalyst. If one epoxide carbon carries a methyl group, conformational and steric factors come into play. C-O bond cleavage at the more substituted carbon, leading to equatorial alcohols, becomes competitive with preferential formation of axial alcohols, and steric hindrance to molecular reorientation on the catalyst causes cis as well as trans hydrogen addition.