Transformations of 3-(1,3-dioxobutan-1-yl)-3H-chromen-2-one during the action of bromine

It was established that the direction of the reaction of 3-(1,3-dioxobutan-1-yl)-2H-chromen-2-one with bromine depends on the conditions under which it is carried out. In acidic media carbocyclization occurs with the formation of dihydroxanthylium bromide or hydroxyxanthene; in chloroform enolization of the carbonyl group with subsequent bromination and heterocyclization to substituted pyranochromene with the participation of the benzopyran-2-one fragment occurs.