Dynamic combinatorial libraries of 2,5-diformylfuran-derived macrocycles.

A series of polyazamacrocycles, containing a furan moiety, have been prepared using the all-in-solution approach of dynamic combinatorial chemistry. The methodology involves the use of a range of simple, fully soluble inorganic salts as templates and fast imine-to-amine reduction followed by high-performance liquid chromatography screening for the best reaction conditions. It offers an elegant and labor-efficient alternative to the classical methodology of imine trapping via crystallization of complexes. For all the presented 2,5-diformylfuran-derived libraries, the templates provided control over the libraries' behavior, which was reflected in increased isolated yields of the corresponding macrocyclic amines, compared to those of nontemplated libraries. The key parameters for achieving true thermodynamic control over the system, which are macrocyclization kinetics and imine reduction kinetics using NaBH4 accompanied by various protic additives, have been discussed.