Assembling phthalaldehyde and o-aminochalcones by Pd(II) catalyzed tandem reaction for synthesizing isoindoloindonole fluorophores

One-pot synthesis of isoindoloindonoles having various auxochrome, from easily available starting materials phthalaldehyde and o-aminochalcone, involving palladium(II) acetate catalysis in acetic acid is reported. A mechanism based on the formation of 2-aryl-2H-isoindol-1-ol (22) intermediate is proposed for the formation of the tetracyclic core of isoindoloindonoles. The possible intramolecular cyclization via the direct participation of the carbonyl vs the adjacent αβ-conjugated double bond was evaluated. Thus, a detailed study on how the presence of electronically different groups at the β position of chalcones affects the outcome of the cyclization reaction and the photophysical properties of the resulting isoindoloindolones is presented here. Furthermore, the core structure was determined using NMR, mass and single-crystal X-ray diffraction analysis.