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.本研究报道了通过轴形成反应的过渡态稳定策略，合成冠醚（crown ether）-铵、酰胺及胺类[2]轮烷（[2]rotaxanes）的方法。相较于轮烷合成中普遍采用的两步“剪切（clipping）”与“封端（capping）”策略，本研究中的组分仅需一步无试剂、动力学控制的反应即可组装为互锁分子。冠醚可通过空腔包裹作用加速轴形成组分的反应，以无金属活性模板合成（metal-free active template synthesis）的方式得到穿线产物。轮烷的形成可通过稳定不同的过渡态实现，这些过渡态包含五配位（5-coordinate，如SN2）或四配位（4-coordinate，如酰化反应、迈克尔加成反应（Michael addition））的碳中心。通过该策略制备的实例包括冠醚-肽轮烷（crown-ether-peptide rotaxanes）与可切换分子梭（switchable molecular shuttles）。