Synthesis of π-Expanded Coumarins by Ligand-Enabled Selective C−H Functionalization

Herein, we report the synthesis of a series of π-expanded coumarin derivatives by the selective C−H alkenylation of β-naphthol in the presence of a palladium catalyst. The use of an anionic thioether ligand is critical for ensuring the high reactivity of this reaction; it enables low catalyst loadings, mild reaction conditions, and the use of acetic acid as a green solvent. This chemistry is widely applicable to naphthol-based aromatic substrates bearing either electron-donating or -withdrawing functional groups. (Figure presented.).