A biocatalytic approach has been designed for the synthesis of optically active piperazinones and 1,4‐diazepanones in aqueous medium under mild conditions. The method described herein is based on a biocatalytic transamination of an easily accessible N‐(2‐oxopropyl) amino acid ester and the subsequent spontaneous cyclization of the initially formed amine. Both enantiomers of the synthesized piperazinones can be prepared by the selection of amine transaminases of opposite selectivity. The reaction conditions were optimised and eight selected processes were performed on a preparative scale. Thus, seven optically active piperazinones were synthesized in high isolated yields (70–90%) and a 1,4‐diazepanone in a moderate yield (51%), being the ee ≥99% in all the cases.