A process for the synthesis of Pirlindole enantiomers of formula II or III or a pharmaceutically acceptable salt thereof, comprising the following steps: reacting compound of formula VI -6-methyl-N-( -1-phenylethyl)-2,3,4,9-tetrahydro-1H-carbazol-1-amine or compound of formula VIII -6-methyl-N-( -1-phenylethyl)-2,3,4,9-tetrahydro-1H-carbazol-1-amine, and an acylating compound of formula XII wherein L 1 is a leaving group selected from ―Br, -Cl, -OTs, -OMs, OH, ―OR1, -OCOR 1 or imidazole, R 1 is hydrogen, C 1 -C 6 alkyl chain or an aryl, in a first aprotic solvent, in the presence of an alkaline agent to yield compound of formula X, 2-substituted N-( -6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-yl)-N-( -1-phenylethyl)acetamide or compound of formula XI, 2-substituted N-( -6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-yl)-N-( -1-phenylethyl)acetamide intramolecular indole acetamide cyclisation of compound of formula X or compound of formula XI wherein L 2 is a leaving group selected from ―Br, -Cl, -I, -OTs, -OMs, -OH, ―OR 1, in a second aprotic solvent, in the presence of an alkaline agent and a phase transfer catalyst to yield compound of formula IV, -8-methyl-3-( -1-phenylethyl)-3a,4,5,6-tetrahydro-1H-pyrazino[3,2,1-jk]carbazol-2 -one or compound of formula XIV -8-methyl-3-( -1-phenylethyl)-3a,4,5,6-tetrahydro-1H-pyrazino[3,2,1-jk]carbazol-2 -one reducing the lactam ring of compound of formula IV or compound of formula XIV into compound of formula V or compound of formula IX, respectively, in a third aprotic solvent, in the presence of a reducing agent and catalytic hydrogenolysis or acidic phenyl cleavage to yield Pirlindole enantiomers of formula II or III or its pharmaceutically acceptable salts. reacting compound of formula VI -6-methyl-N-( -1-phenylethyl)-2,3,4,9-tetrahydro-1H-carbazol-1-amine or compound of formula VIII -6-methyl-N-( -1-phenylethyl)-2,3,4,9-tetrahydro-1H-carbazol-1-amine, and an acylating compound of formula XII wherein L 1 is a leaving group selected from ―Br, -Cl, -OTs, -OMs, OH, ―OR1, -OCOR 1 or imidazole, R 1 is hydrogen, C 1 -C 6 alkyl chain or an aryl, in a first aprotic solvent, in the presence of an alkaline agent to yield compound of formula X, 2-substituted N-( -6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-yl)-N-( -1-phenylethyl)acetamide or compound of formula XI, 2-substituted N-( -6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-yl)-N-( -1-phenylethyl)acetamide intramolecular indole acetamide cyclisation of compound of formula X or compound of formula XI wherein L 2 is a leaving group selected from ―Br, -Cl, -I, -OTs, -OMs, -OH, ―OR 1, in a second aprotic solvent, in the presence of an alkaline agent and a phase transfer catalyst to yield compound of formula IV, -8-methyl-3-( -1-phenylethyl)-3a,4,5,6-tetrahydro-1H-pyrazino[3,2,1-jk]carbazol-2 -one or compound of formula XIV -8-methyl-3-( -1-phenylethyl)-3a,4,5,6-tetrahydro-1H-pyrazino[3,2,1-jk]carbazol-2 -one reducing the lactam ring of compound of formula IV or compound of formula XIV into compound of formula V or compound of formula IX, respectively, in a third aprotic solvent, in the presence of a reducing agent and catalytic hydrogenolysis or acidic phenyl cleavage to yield Pirlindole enantiomers of formula II or III or its pharmaceutically acceptable salts.