Spontaneous macrocyclization via recombination of a Schiff-base linkage

A macrocyclic compound that has two salenH2 moieties was synthesized via recombination of an acyclic Schiff base in quite high yield, and was characterized by X-ray crystallography. The recombination occurred in a slow diffusion system of chloroform–methanol, where the starting material may spontaneously form a molecular assembly suitable for the subsequent reaction. This assumption was supported by the crystal structure of an analogue of the acyclic Schiff base.