Pd-Catalyzed Synthesis of 3-Bromo-2H-Chromenes

Significance

Reported is the Pd-catalyzed synthesis of 3-bromo-2H-chromenes, further mediated by copper and lithium bromide. The reaction does not work if palladium acetate, copper bromide or lithium bromide are excluded. It is postulated but not proved that the presence of lithium bromide is required to increase the concentration of bromide ions in solution to promote ligand exchange between acetate and bromide. A screening of different reaction conditions was noted, but not delineated. The substrate scope was poorly investigated.