STEREOCHEMICAL CONTROL BY CARBOXYLATE GROUPS IN HOMOGENEOUS HYDROGENATION

Article abstract of DOI:10.1016/0022-328X(85)87378-2

The stereochemistry of hydrogenation of a range of unsaturated cyclohexane-carboxylic acids and their esters has been investigated, employing either bis(1,4-diphenylphosphino)butanerhodium or pyridine(tricyclohexylphosphine)iridium based cationic catalysts in CH2Cl2.For methyl 3-methylcyclohex-2-enecarboxylate, highly selective reduction to the trans-product was achieved in both cases, whereas the isomeric methyl 3-methylenecyclohexanecarboxylate gave appreciable amounts of the cis-isomer.A predominance of trans-isomer was also achieved in the reduction of methyl 4-methylcyclohex-3-ene carboxylate, in a rather slower reaction.Reductions with D2 revealed that considerable isomerisation of the olefinic double bond occurred during hydrogenation.The corresponding unsaturated acids were reduced with moderate to high selectivity but reaction was either very slow, or ceased after a few turnovers.Related cyclohexadienecarboxylates were unreactive to homogeneous hydrogenation with cationic catalysts.