Tuning of Aromaticity in Meso‐Thienyl 22‐Oxabenzonorroles

Meso ‐thienyl 22‐oxabenzonorroles containing one to three thienyl groups at the meso ‐positions were synthesized over sequence of four simple steps in 11%–15% yields using readily available oxabenzobilanes as the key precursors. Interestingly, in meso ‐monothienyl 22‐oxabenzonorrole and meso ‐trithienyl 22‐oxabenzonorrole, the chloro group was present at the inner core carbon of indole moiety of respective 22‐oxabenzonorrole macrocycle whereas chloro was not present at the inner core carbon of meso ‐(bis)thienyl 22‐oxabenzonorrole. The X‐ray crystallography revealed that the meso ‐(bis)thienyl 22‐oxabenzonorrole was almost planar like previously reported meso ‐tritolyl 22‐oxabenzonorrole whereas the meso ‐monothienyl 22‐oxabenzonorrole was nonplanar and the chloro substituted indole ring was deviated by an angle of 52.02° from the mean plane. NMR, NICS, and AICD studies indicated a possibility of tuning the aromaticity in the meso ‐thienyl 22‐oxabenzonorroles depending on the presence of chloro group on inner core carbon of the macrocycles. The meso ‐monothienyl 22‐oxabenzonorrole and meso ‐trithienyl 22‐oxabenzonorrole were relatively less aromatic than meso ‐(bis)thienyl 22‐oxabenzonorrole. The absorption spectra of meso ‐thienyl 22‐oxabenzonorroles displayed sharp and well‐defined absorption bands spanning over the visible region and the electrochemical studies indicated the electron rich nature of the macrocycles. DFT and TD‐DFT studies were in agreement with the experimental observations.