One-pot synthesis of terpyridines and macrocyclization to C3-symmetric cyclosexipyridines

Abstract

Four examples of 2,6-dicinnamoylpyridines were obtained in 60–65% yields in condensations of commercially available 2,6-diacetylpyridine and benzaldehydes in 1:2 stoichiometry. At 2:1 ratios, four related 6,6''-diacetylated-4'-arylterpyridines were isolated in 70–73% yields in one-pot condensations in the presence of NH3. 4,4'-Azo benzaldehyde, prepared from nitrobenzaldehyde in three steps and 40% overall yield was similarly converted to a novel azo-linked bis(terpyridine) in 50% yield in a reaction that assembles seven molecules in one step. The 6,6''-diacetylated-4'-arylterpyridines and the correspondingly substituted 2,6-dicinnamoylpyridines were condensed in 1:1 ratio together with NH3 to form 4,4'',4IV-triarylcyclosexipyridines in 22–26% yields. These were obtained as mixed Na+ and K+ complexes and were insoluble amorphous solids, except for one example bearing 4-neopentoxyphenyl substituents. 1H NMR showed that the 4,4'',4IV-tri(4-neopentoxyphenyl)cyclosexipyridine complexes form aggregates in solution and at low concentrations show twofold symmetry arising from a loss of planarity.Key words: terpyridines, 4'-aryl-6,6''-diacetylterpyridines, azo-bisterpyridine, cyclosexipyridines, macrocyclization.