Reversible Macrocycle-to-Macrocycle Interconversion Driven by Solvent Selection

Macrocycle-to-macrocycle interconversions are of interest because they can allow access to a variety of structures. However, reversible interconversion between different sized macrocycles remains challenging to control. Herein, we report a facile one-pot synthesis of a series of self-assembled macrocycles from readily prepared α,α'-linked oligopyrrolic dialdehydes and various alkyl diamines. The condensation of pyridine-bridged oligopyrrolic dialdehyde 3 and simple alkyl diamines proved independent of solvent, always yielding the [2 + 2] macrocyclic products. However, when 3 was condensed with 2,2'-oxybis(ethylamine) 14, either ([1 + 1] or [2 + 2]) products are obtained depending on the choice of solvent. Reaction of 3 and 14 in methanol, ethanol, or chloroform gave the [1 + 1] macrocycle as the sole product. In contrast, condensation of 3 and 14 in dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), or acetonitrile (MeCN) yielded the [2 + 2] macrocycle as the major product in the form of a precipitate. Reversible interconversion between the [1 + 1] and [2 + 2] macrocycles could be achieved by tuning the solvent, with the ratio driven by thermodynamic and solubility considerations.