Intermolecularly hydrogen-bonded dimeric helices: tripyrrindiones

A rare and unusual class of tripyrrolic compounds, violet-colored tripyrrin-1,14-diones, can be prepared easily and in moderately high yields from base (piperidine)-catalyzed condensation of 3-pyrrolin-2-ones with 2,5-diformylpyrroles. Dipyrrinones adopt the all- syn- Z conformation leading to helical, lock-washer like structures, which form dimers that are held together by intermolecular hydrogen bonds in nonpolar solvents and in the crystal. Strong bathochromic spectral shifts of the tripyrrindione ∼480 nm long wavelength UV–visible absorption band are seen with added base: DBU, 615 nm; TFA, 573 nm; and Zn(OAc) 2, 586 nm. Tripyrrindiones, a rare class of violet-colored tripyrrolic compounds, can be prepared from 3-pyrrolin-2-ones and pyrrole-2,5-dialdehydes and form intermolecularly hydrogen-bonded dimers in CDCl 3 and in the crystal. [Display omitted]