Precise Control of Radial Catenane Synthesis via Clipping and Pumping.

An unprecedented molecular pumping cassette was designed and implemented for the construction of molecular necklaces, that is, radial [ n ]catenanes. The mechanism was fully confirmed on a model [2]pseudorotaxane, and the novel clipping-followed-by-pumping strategy was used to prepare a series of [ n ]catenanes ( n = 2-5). A pair of [3]catenane diastereomers sequentially threaded with two different wheels was also accomplished. The success of utilizing molecular pumping to construct molecular necklaces offers new insights into complex molecular architectures and expands the application of molecular machines in synthesis.