Chalcone dihalides—VIII: Synthesis and cyclization of the stereoisomers of 2′,6′-disubstituted α-bromochalcones

2′-Acetoxy-6′-methoxychalcone dibromides reacted with ethanolic potassium acetate to form the cis and trans isomers of the corresponding 2′-acetoxy-α-bromochalcones. 2′-Hydroxychalcone dibromides reacted similarly but, in two cases, some ring closure also occurred. The stereoisomers of the α-bromo-2′-hydroxy-6′-methoxychalcones were cyclized with aqueous ethanolic potassium hydroxide. In keeping with their proposed intermediacy in the Emilewicz-von Kostanecki reaction, they yielded both flavone and aurone and aurone formation was related to the hydroxide concentration. The trans isomers more readily formed aurones.