Scheme 2.
Molecular trefoil knots prepared from a linear helicate strategy. a) Synthesis of trefoil knot Cu2 5 a after covalent capture of linear double helicate Cu2 4 a 2 by Williamson ether synthesis.64 b) The yield of the trefoil knot was significantly increased by using RCM for the macrocyclization reactions.65 c) X‐ray structure of the related trefoil knot Cu2 5 c. This early design was obtained in lower yield, as the alkyl chain connecting the phenanthroline units is less preorganized than the m‐phenylene unit used in later designs.63 d) A related approach using FeII and terpyridine derivatives instead of CuI and phenanthroline ligands.66 e) Enantioselective synthesis of a trefoil knot by the linear helicate approach.68