This invention relates to a process for the preparation of pyrido[2,1-a]isoquinoline derivatives of the formula wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are defined in the specification, comprising the optical resolution of an enamine of the formula wherein R.sup.1 is lower alkyl, in the presence of an optical active resolving agent to form an (S)-enamine salt of the formula wherein RCO.sub.2.sup.- is the conjugate base of the resolving agent.