A surprising double carbon–nitrogen coupling reaction catalyzed by [H3Ru4(C6H6)4(OH)]2+: synthesis of unusual barbiturate analogues

Seven- and eight-membered analogues of barbituric acid are easily accessible by insertion of carbodiimides into cyclic anhydrides catalyzed by the cationic hydroxo cluster [H3Ru4(C6H6)4(OH)]2+.