Ligand-Free Cyclocarbonylation of ortho-Iodophenols and Acetylenes to Chromones

Significance

Reported is the palladium-catalyzed synthesis of chromones via cyclocarbonylation of ortho-iodophenols followed by reaction with terminal acetylenes in an ionic liquid. Other palladium sources and ionic liquids were briefly ­investigated but afforded either lower yields or required higher CO pressures than those shown. Lowering the catalyst loading (1 mol%) and recycling the ionic liquid/active catalyst mixture were investigated, with a slight decrease in yield observed in both cases (95 to ˜80%). The substrate scope was well studied in terms of alkyne, not so with respect to the iodophenol counterpart.