Quantitative Active Transport in [2]Rotaxane Using a One-Shot Acylation Reaction toward the Linear Molecular Motor

A rotaxane consisting of a crown ether wheel and a secondary ammonium salt axle, on which a neopentyl-type end-cap was placed close to the ammonium moiety, was prepared. When the rotaxane was treated by excess triethylamine, the wheel component thermodynamically moved over the proximate neopentyl group to deconstruct the interlocked structure. The wheel component in the rotaxane, however, quantitatively moved against the proximate end-cap by the action of trifluoroacetic anhydride in the presence of excess triethylamine. This motion, which was driven by the simple one-shot acylation reaction, can be referred as the active transport. When the distant end-cap is of the neopentyl-type, the axle can be thermally dethreaded from the distant end-cap after the acylative transport. The series of the wheel movement controlled by the neopentyl group can be the basic motion of the unidirectional linear molecular motor.