AMINE-EFFECTED CYCLIZATION OF CHALCONE DIHALIDES TO AURONES

The possibility of employing the amine-catalysed cyclization of αβ-dibromodihydrochalcones and α-bromochalcones as a general synthesis of aurones was studied using cyclohexylamine and the most representative member of each class of these αβ-disubstituted ketones and α-halogeno chalcones. Overall yields of heterocyclic products were generally poor except from 4'6'-dimethoxy- and 3-nitro- substituted chalcone systems; aurones were obtained in fair yield from the former and in excellent yield from the latter. 22'-Diacetoxychalcone dibromide and 22'-diacetoxy-α-bromochalcone cyclised to a 2-benzoylbenzofuran to the exclusion of the corresponding aurone and flavone. © 1990.