Benzopyrones. Part I. 6-Amino- and 6-hydroxy-2-substituted chromones
Contrary to a report in the literature, mono- and di-nitration of 6-hydroxy-2-methylchromone (I) gives the 5-nitro- and the 5,7-dinitro-derivative according to the conditions. 2,5-Dihydroxy-3-nitroacetophenone, whose m.p. is given erroneously in the literature, has been synthesized. The earlier literature on mono- and di-bromination of (I) is corrected and the structure of each product is elucidated.
4-Oxochromen-2-carboxylic acid and its ethyl ester have been nitrated; the catalytic hydrogenation of the resulting 6-nitro-compound has been studied; according to the conditions, the products are the 6-hydroxyamino-and the 6-amino-chromone (VIII), and the 6-aminochromanone. Diazotization of (VIII) followed by hydrolysis gave 6-hydroxy-4-oxochromen-2-carboxylic acid.