Palladium-Mediated\nSite-Selective C–H Bond\nActivation and Arylation of 9(10<i>H</i>)‑Acridinone\nand Mechanistic Investigation: Stoichiometric and Catalytic Approaches

Palladium-mediated site-selective C–H bond activations\nof\n9(10<i>H</i>)-acridinone, resulting in the formation of\n4- and 1-arylated 9(10<i>H</i>)-acridinones, are presented\nthrough the use of both stoichiometric and catalytic experiments.\nIn the stoichiometric reactions, two distinct classes of acridinone\npalladacycles are generated via C (4)–H and C (1)–H\nbond activations, with the pyridine and ketone groups serving as the\ndirecting group, respectively. The constitutional conformation and\nthermal stability of these palladacycles were elucidated through both\nX-ray crystallography and NMR spectroscopy. Additionally, an investigation\nwas conducted into the interconversion of C (4 and 1)–H bond-activated\npalladacycles in trifluoroacetic acid and acetic acid. During the\ncourse of C (1)–H bond arylation, a serendipitous discovery\nled to the isolation of a chromeno [4,3,<i>2-kl</i>] acridinone\ncompound as a byproduct, showcasing good fluorescence properties.\nControlled experiments, kinetic isotope effect study, key palladacycles,\nand the formation of corresponding products support the proposed mechanisms\nfor these presented reactions. Finally, the pyridinyl group can serve\nas a removable directing group and can be readily eliminated from\nboth 4- and 1-arylated 9(10<i>H</i>)-acridinones.