Process for the preparation of piperazine ring for the synthesis of pyrazinocarbazole derivatives

The present disclosure relates to an improved process for the synthesis of piperazine ring, particularly for the preparation of heterocyclic compounds useful as intermediates in the synthesis of pyrazinocarbazoles such as the antidepressant Pirlindole. The process described is useful to prepare Pirlindole enantiomers, or a pharmaceutically accepted salt thereof.