Process for the preparation of (R)-4-propyl pyrrolidine-2-one, a key intermediate for synthesis of brivaracetam

A process for the preparation of (25)-2-[(4R)-2-oxo-4-propyl-pyrrolidin-1-yl] butanamide (brivaracetam) having the structure:

• comprising:
• (a) stereoselective hydrolysis of dimethyl 3-propylpentanedioate of formula (III)
• using Novozyme's Promea®, a lipase liquid enzyme having the enzyme commission designation EC 3.1.1.3, in the presence of a buffer solution at a pH from 7.0 to 9.0 and a temperature from 15° C. to 30° C. to obtain (S)-3-(2-methoxy-2-oxoethyl) hexanoic acid of formula IV
• (b) reacting the compound of formula (IV) with ammonia in dichloromethane, in the presence of methyl chloroformate and base N-methylmorpholine or triethylamine at a temperature from −20° C. to 0° C. to obtain methyl (S)-3-(2-amino-2-oxoethyl) hexanoate of formula V
• (c) reacting the compound of formula (V) with hydrochloric acid in the range from 1.0M to 4.0M solution at a temperature from 20° C. to 40° C. to obtain (S)-3-(2-amino-2-oxoethyl) hexanoic acid of formula VI
• (d) converting the compound of formula (VI) by Hofmann rearrangement using tricholoroisocyanuric acid and sodium hydroxide in water at a temperature from 15° C. to 30° C., and later at a temperature from 85° C. and 100° C. to obtain (R)-4-propyl-pyrrolidin-2-one (I)
• and
• (e) converting the compound of formula (I) into (2S)-2-[(4R)-2-oxo-4-propyl-pyrrolidin-1-yl]butanamide (brivaracetam).