Mechanical activation of a beta-lactam mechanophore using ultrasound induces a formal [2 + 2] cycloelimination reaction producing ketene and imine functional groups-the reverse reaction of the Staudinger cycloaddition. This transformation is predicted by computational modeling and verified by kinetics and UV-vis absorption measurements as well as polymer end-group analysis using H-1 and C-13 NMR spectroscopy. Addition of the beta-lactam motif to the current repertoire of covalent mechanophores coupled with the diverse reactivity of the ketene functional group provides a promising new platform for achieving materials capable of autonomic self-healing behavior in response to external forces.