Synthesis and Properties of 10‐Aryl‐11H‐indeno[2,1‐a]azulenes and Azuleno[2,1‐a]indenones

An efficient synthesis of 10‐aryl‐11 H ‐indeno[2,1‐ a ]azulenes has achieved via [8 + 2] cycloaddition between 8‐aryl‐cyclohepta[ b ]furan‐2‐ones with an enamine is generated from 1‐indanone and pyrrolidine in good yields. Oxidation of 10‐aryl‐11 H ‐indeno[2,1‐ a ]azulenes with 2,3‐dichloro‐5,6‐dicyano‐ p ‐benzoquinone in aqueous acetone shows complete decomposition, whereas chlorinated derivatives undergoes the oxidation to afford the corresponding azuleno[2,1‐ a ]indenones in moderate to good yields. Single‐crystal X‐ray diffraction analysis reveals that the 11 H ‐indeno[2,1‐ a ]azulene and azuleno[2,1‐ a ]indenone cores are remarkably planar, while the appended aryl groups adopt a nearly orthogonal orientation owing to steric hindrance, thereby limiting conjugative interactions. Ultraviolet‐visible and fluorescence spectroscopic investigations, supported by time‐dependent density functional theory calculations, indicated that the optical transitions are predominantly localized on the azulene unit and are subtly modulated by the electronic nature of the aryl substituents. In addition, electrochemical studies also demonstrate systematic variations in redox potentials according to the electronic characteristics of the aryl groups.