Starting from the diastereomerically pure 4-ethenyl pyrrolidin-2-one 5, through simple steps the mesyl derivative 8 was obtained, which underwent intramolecular alkylation to give, in good yield, the 3-aza-2-oxobicyclo [3.1. 0] hexane 9. This compound was subsequently converted into enantiomerically pure (−)-cis-2, 3-methano-GABA, 2.