Synthesis of catenanes and molecular knots by copper(I)-directed formation of the precursors followed by ruthenium(II)-catalysed ring-closing metathesis

Abstract

Catenanes and knots are fascinating molecular systems, but for several decades these compounds have been regarded as exotic species due to synthetic difficulties. We have proposed template strategies based on transition metals (mostly copper(I)), and this approach has allowed us to make a wide family of interlocking rings and knots in the course of the last 15 years. A very recent and practically important improvement now permits relatively easy preparation of some of these systems with, in some cases, almost quantitative yields. The key step is the ring-closing metathesis (RCM) of olefins, using the extremely efficient and mild catalysts developed by Grubbs et al. in the last few years, and consisting of ruthenium carbenes.