(1S,2S,5R,6R)-3-Azatricyclo[4.2.1.02,5]non-7-en-4-one is a carbocyclic β-lactam. It is used in the asymmetric synthesis of enantiopure carbocyclic β-amino acids via Candida antarctica lipase catalyzed solvent-free vapor-assisted enantioselective hydrolytic ring opening of carbocyclic β-lactams. (1S,2S,5R,6R)-3-Azatricyclo[4.2.1.02,5]non-7-en-4-one is the starting racemate for 1,4-ethylene-bridged cispentacin.