1968 Volume 41 Issue 12 Pages 2949-2953
6-Hydroxy-2,3-benzotropone (or 3-hydroxy-4,5-benzotropone) (I) was brominated under various conditions, and the bromination products were subjected to debromination, substitution, and some other reactions. I reacted with a molar equivalent of bromine at 25°C to give 7-bromo-6-hydroxy-2,3-benzotropone (II), and with two molar equivalents of bromine at 25°C to give an adduct of II with bromine (V), which, on heating, was dehydrobrominated to 5,7-dibromo-6-hydroxy-2,3-benzotropone (IV). On the other hand, I reacted with bromine at 100°C to give 5-bromo-6-hydroxy-2,3-benzotropone (III), IV, and 2,2,7-tribromo-4,5-benzocyclohepta-4,6-diene-1,3-dione (VI), depending on the amount of bromine employed. All these bromination products could be debrominated with ease with hydrogen in the presence of catalyst to yield I. When II was heated with hydrobromic acid, the 7-bromo substituent was in part eliminated to give I and migrated in part to give III. When IV and 4,7-dibromo-6-hydroxy-2,3-benzotropone (X) were heated with hydrobromic acid, the 7-bromo substituents were eliminated and the 4- or 5-bromo substituent remained unreacted, producing III and 4-bromo-6-hydroxy-2,3-benzotropone (IX) respectively. When II and IV were heated with hydrochloric acid, the 7-bromo substituents were not eliminated but, rather, substituted with chlorine atoms to give 7-chloro-6-hydroxy-2,3-benzotropone (VII) and 5-bromo-7-chloro-6-hydroxy-2,3-benzotropone (VIII) respectively. These facts suggest that I and its bromo derivative sometimes behave as unsaturated β-diketones (I′).
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