Process for the preparation of the Z-isomer of 3-(4-bromophenyl)-N-methyl-3-(3-pyridyl)-allylamine

The Z-isomer of 3-(4-bromophenyl)-N-methyl-3-(3-pyridyl)-allylamine of the formula (I) or one of its pharmaceutically acceptable acid addition salts exhibits a highly selective inhibitor action on the neuronal uptake of 5-hydroxytryptamine and can be used as an antidepressant or neuroleptic. The said compound is prepared by dehydrating a compound of the formula (II) and recrystallising the resulting stereoisomer mixture repeatedly from a solvent in which the two E- and Z-isomers show a substantially different solubility. The pure Z-isomer is isolated. The dehydration is preferably carried out with sulphuric acid, hydrochloric acid, phosphoric acid, potassium hydrogen sulphate or oxalic acid, especially by heating, or by catalytic dehydration by treatment with kaolin, mineral alumina or aluminium oxide, especially at a temperature of 300 to 500 DEG C. Preferably, the compound of the formula (I) is recrystallised three times as the oxalate from ethanol.