Rh(III)-Catalyzed Annulation of Enaminones with Sulfoxonium Ylides: Access to Isoquinolines and Benzo[ de ]chromenes

A Rh(III)-catalyzed annulation of enaminones 1 with sulfoxonium ylides 2 has been developed for the efficient synthesis of functionalized isoquinolines 3. Unlike conventional carbonyl-directed C-H functionalization, the observed site selectivity may be associated with Lewis acid-enaminone interactions, which could facilitate aryl C(sp2)-H activation. Under aerobic conditions, diverse substrates undergo annulation in the presence of [Cp*RhCl2]2, AgOAc, and PivOH in toluene, affording the desired products in moderate to excellent yields. Mechanistically, the transformation likely involves C-H activation, migratory insertion, protonation, and intramolecular condensation, resulting in a formal [4 + 2] annulation that simultaneously forms C-C and C-N bonds. Furthermore, the resulting isoquinolines 3 were readily transformed into structurally complex benzo[de]chromenes 5, highlighting the synthetic versatility of this methodology for the preparation of biologically relevant molecular scaffolds. These benzo[de]chromenes also exhibit notable fluorescence properties, thereby broadening their prospects for future applications.