Substituted 4H-1-benzopyran-4-ones (chromones): synthesis via palladium-catalysed coupling of their halogeno derivatives with alkenes
Activation of bromochromones has been achieved by Pd0 insertion into the carbon–halogen bond. The resultant species undergo coupling with alkenes leading to vinylated chromones. Vinylation occurs regiospecifically at the original site of bromination and therefore provides a method for the clean introduction of substituents into the chromone ring system. An anomalous reaction of a dibrominated chromone leading to a ring-opened product is described.