The condensation of 2-pyrrolidone (I) with 2-oxobutyric acid (II) in refluxing toluene gives 2-(2-oxopyrrolidin-1-yl)-2-butenoic acid (III), which is treated with PCl5 in THF to yield the acyl chloride (IV). The reaction of (IV) with dry ammonia affords the corresponding amide (V), which is finally submitted to an asymmetric hydrogenation with H2 over a chiral Rh catalyst to provide the desired chiral butyramide.

Reductive amination of 5-hydroxy-4-propyl-2-furanone (I) with (S)-2-aminobutyramide (II) in the presence of NaBH4 yields the dihydropyrrolone (III). Transfer hydrogenation of (III) with ammonium formate and Pd/C provides a diastereoisomeric mixture of pyrrolidinones, from which the title compound is isolated by preparative HPLC on chiral phase.