Synthesis, Structure and Studies of Meso-Triaryl 22-Oxabenzonorroles.

The first examples of meso-triaryl 22-oxabenzonorroles were synthesized in 18-21% yields by oxidation of appropriate meso-triaryl oxabenzobilane. The key precursors, the meso-triaryl oxabenzobilanes were synthesized readily by treating 16-oxatripyrrane with (1H-indol-3-yl)(p-tolyl)methanol under acid catalyzed conditions. The meso-triaryl 22-oxabenzonorroles were obtained in free base form by following our simple straight-forward synthetic strategy. The X-ray structure obtained for meso-tritolyl 22-oxabenzonorroles revealed that the indole ring was deviated by an angle of 41.27° from the mean plane. The NMR studies supported the presence of diatropic ring current effect as inner NH and CH protons were observed in the upfield region. The absorption spectra of 22-oxabenzonorroles exhibited one strong Soret band and four weak Q-bands. The electrochemical studies revealed that the macrocycles are electron rich and undergo easier oxidations. The DFT and TD-DFT studies were in agreement with the experimental observations and NICS and HOMA values supports the aromatic nature of meso-triaryl oxabenzonorroles.