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.