Direct monobromination of substituted 4-oxoquinoline-3-carboxylic acid derivatives

N-Bromosaccharin in the presence of pyridinium poly(hydrogen fluoride) can be used for monobromination of ethyl esters of 6- and 7-substituted-4-oxo-1,4-dihydroquinoline-3-carboxylic acids. The reactions take place at the C₆ or C₈ positions, depending on the types and positions of the substituents.