Highly Chemoselective One-Step Synthesis of Novel N-Substituted-Pyrrolo[3,4-b]quinoline-1,3-diones via Palladium-Catalyzed Aminocarbonylation/Carbonylative Cyclisation Sequence

Novel N-substituted pyrrolo[3,4-b]quinoline-1,3-diones have been prepared via a highly chemoselective palladium-catalyzed carbonylative imidazation-cyclization reaction in a one-pot synthetic approach. This methodology, which has been applied for the first time to access such original scaffolds through two different protocols involving 3-bromo-2-iodoquinoline, as a typical partner, primary amines, and atmospheric or high carbon monoxide pressure (20 bar), has shown an excellent tolerance for many functional groups. The use of bidentate ligands such as XantPhos and dppp, either under atmospheric or high-pressure conditions, provides a wide range of carbonylated compounds in good to excellent yields (up to 82 %). Furthermore, some new quinoline-2,3-dicarboxamides have been isolated as side products in very low yields and have been fully characterized. The solid state structures of three of the synthesized acridinimides have been unequivocally established by single-crystal XRD analysis.