Synthesis of Pyrrolo[2,3-]isoquinolines via the Cycloaddition of Benzyne with Arylideneaminopyrroles: Photophysical and Crystallographic Study.

An efficient and quick access toward a series of ()-2-arylideneaminopyrroles and to their benzyne-promoted aza-Diels-Alder cycloaddition products is provided. These products are three pyrrolo[2,3-]isoquinolines substituted in position 5 with different electron-acceptor (A) or electron-donor (D) aryl groups. Intermediates and products were obtained in good yields (up to 78 and 84%, respectively), and their structures were determined on the basis of NMR measurements and HRMS analysis. Photophysical properties of were investigated, finding good Stokes shift in different solvents, but only the product showed appreciable fluorescence intensity since its 5-aryl group (2,4-ClPh) could favor the twisted intramolecular charge transfer effect. In addition, a riveting relationship between solvent viscosity and fluorescence intensity was found. Structures of and were studied and confirmed by single-crystal X-ray diffraction, observing that their electronic distributions effect the supramolecular assembly but with only long-distance hydrophobic interactions. A CE-B3LYP model was used to study the energetic topology and understand the crystal architecture of compounds as well as find a connection with both the synthetic and photophysical results.