Synthetic experiments in the benzopyrone series - Part XVIII. Use of N-bromo-succinimide for the synthesis of flavones
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Use of N-bromo-succinimide for the conversion of flavanones into flavones is investigated. 7-Methoxy-flavanone undergoes bromination in the 3-position and on treatment with alcoholic sodium hydroxide solution gives rise to a good yield of 7-methoxy-flavone. On the other hand, 5:7-dimethoxy flavanone suffers nuclear bromination more prominently and yields a mixture of products containing 8-bromo-5:7-dimethoxy-flavanone and the 3:8-dibromo compound. Naringenin acetate yields as the major product apigenin acetate, as the result of substitution in the 3-position and subsequent elimination of hydrogen bromide; the other product is 3-bromonaringenin acetate which undergoes conversion into apigenin with alkali. Acetates therefore appear to be the most convenient derivatives for this reaction.