Unprecedented formation of azulicorroles from the scrambling of azulitripyrrane

Abstract

In this study, we have prepared new tripyrranes embedded with azulene bearing two meso-pentafluorophenyl substituents. They were obtained as diastereomers in high yield which were separated using conventional column chromatography. Their distinct solution structures were unambiguously confirmed by NMR and mass analysis. Our synthetic strategy is simple and straightforward due to the reactivity of 1,3-positions of azulene, which underwent Lewis acid-catalyzed condensation with pyrrole-2-carbinol. These diastereomers were further subjected to acid-catalyzed (CF3COOH) condensation with pyrrole dicarbinol to afford the target N-confused azuliporphyrin (reduced form) in trace amount. However, we obtained the tris-meso-pentafluorophenyl substituted azulicorrole (AzCorA) as major product due to an unprecedented scrambling of the azulitripyrranes. The structural characterization of newly synthesized key precursors and macrocycles was done with the aid of high-resolution mass analyses, and 1H and 2D NMR analyses. The single crystal X-ray structure obtained for AzCorA revealed that the azulene subunit is tilted by 34.03[Formula: see text] due to the steric congestion of inner-NHs.