Highly efficient synthesis of [3]rotaxane assisted by preorganisation of pseudorotaxane using bis(crown ether)s

摘要

The tether-assisted synthesis of [3]rotaxane by olefin metathesis has been studied in detail. Bis(crown ether)s, in which two crown ethers are connected by a linker, were threaded onto ammonium salts bearing a terminal olefin to form pseudorotaxanes. The pseudorotaxanes were converted into tethered rotaxanes in the presence of Grubbs catalyst, followed by removal of the linkers to produce [3]rotaxanes in excellent yields. Preorganisation of the two reactive ends has led to a great improvement in the yield of [3]rotaxanes. The ring strain of the tethered rotaxanes and the flexibility of the pseudorotaxanes were responsible for the formation of the tethered rotaxanes.