Selective Scission of Orthogonal Bonds in Four-Membered Ring Mechanophores upon Activation by a Rotaxane Actuator.

Mechanophores (mechanosensitive molecules) are usually activated by pulling force transduced by polymer covalently attached to their structures. A variety of mechanophores have been described to date but many rely on a limited number of core structures. The diversity of products formed mechanochemically could be improved by promoting the scission of varied bonds within a single mechanophore. 4-membered rings are particularly suited for this as two sets of products can be obtained by formal retro-[2 + 2] cycloaddition depending on the pulling direction. This concept has been applied to a couple of mechanophores but the repositioning of the anchoring points often requires a redesign of the structures, and the pulling activation is not amenable to the release of the products. Here we show that the unique pushing activation of a rotaxane actuator enables the selective activation of covalent bonds parallel or perpendicular to the main chain in diazetidinone and β-lactam mechanophores. The selectivity depends on the orientation of the bulky substituents pointing toward or away from the incoming macrocycle. We were able to release ketene and triaryl imine/ethene molecules, and to generate imine, azobenzene, and isocyanate units. This alternative activation method demonstrates how to elicit new reactivity from known mechanophores and should inspire the design of new ones. The variety of structures released/generated here illustrate how this approach can be used for the release of reactive species and other functional molecules.