Base-Selective Five- versus Six-Membered Ring Annulation in Palladium-Catalyzed C-C Coupling Cascade Reactions: New Access to Electron-Poor Polycyclic Aromatic Dicarboximides.

Palladium-catalyzed base-selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki-Miyaura cross-coupling and direct C-H arylation afforded a series of new five- and six-membered ring annulated electron-poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs2 CO3 ) as auxiliary base in these C-C coupling cascade reactions led exclusively to six-membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five-membered ring annulated products. This base-dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X-ray analysis of the respective five- and six-membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry.