The synthesis of opticallyactive 4-methyl-5-n-butyl- and 5-n-pentylpyrrolidin-2-ones, aza analogues of the corresponding Quercus lactones, has been achieved by a chemoenzymatic procedure, involving in the enantiodifferentiating step the enzymatic kinetic resolution of the corresponding γ-ketoester precursors, followed by reductive amination and subsequent cyclization of the enantiomerically pure hydrolysis