Spontaneous Assembly of Rotaxanes from a Primary Amine, Crown Ether and Electrophile

We report the synthesis of crown ether-ammonium, amide and amine [2]­rotaxanes via transition state stabilization of axle-forming reactions. In contrast to the two-step “clipping” and “capping” strategies generally used for rotaxane synthesis, here the components assemble into the interlocked molecule in a single, reagent-less, step under kinetic control. The crown ether accelerates the reaction of the axle-forming components through the cavity to give the threaded product in a form of metal-free active template synthesis. Rotaxane formation can proceed through the stabilization of different transition states featuring 5-coordinate (e.g., S_N2) or 4-coordinate (e.g., acylation, Michael addition) carbon. Examples prepared using the approach include crown-ether-peptide rotaxanes and switchable molecular shuttles