by enantioselective asymmetric hydrogenation of dehydrositagliptin of Formula (IIa):

and employing a rhodium catalyst on a bisphosphine ferrocenyl ligand selected from the group consisting of Ligand L3, Ligand L6, Ligand L7, and Ligand L8, wherein:

(a) Ligand L3 is 1,1′-Bis [2,5-dimethylphospholano] ferrocene:

(b) Ligand L6 is 1,1′-Bis [2,5-diethylphospholano] ferrocene:

(c) Ligand L7 is 1,1′-Bis (2,5-di-isopropylphospholano) ferrocene:

and

(d) Ligand L8 is 1,1′-Bis ((2,5)-2,5-di-ter-butylphospholano) ferrocene:

(i) mixing the compound of Formula (IIa) with the rhodium catalyst, the bisphosphine ferrocenyl ligand, and an additive to obtain a first reaction mixture, wherein the additive is selected from the group consisting of salicylic acid, acetic acid, ammonium chloride, phosphoric acid, ammonium salicylate, butyl phosphoric acid, dibutyl phosphate, and tributyl phosphate;

(ii) adding a solvent in the first reaction mixture of (i) in an inert atmosphere of argon and stirring at a temperature of 25° C. for one hour to obtain a reaction slurry, wherein the solvent is methanol;

(iii) maintaining the reaction slurry obtained in (ii) under a hydrogen pressure of 10 bar to 30 bar at a temperature of 35° C. to 90° C. for 17 hours to 24 hours in an autoclave, followed by cooling at a temperature of 25° C. and releasing pressure to obtain a second reaction mixture; and

(iv) passing the second reaction mixture of (iii) through a neutral alumina bed followed by collecting a filtrate and drying a residue to afford the compound of Formula (Ia) with an enantiomeric excess of from 83% to 99.9%.