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., SN2) or 4-coordinate
(e.g., acylation, Michael addition) carbon. Examples prepared using
the approach include crown-ether-peptide rotaxanes and switchable
molecular shuttles.