Intermolecular Bromine Transfer of 2-Amino-7-bromotropone Derivatives Catalyzed by Strong Acid

Article abstract of DOI:10.1246/bcsj.58.2840

Upon heating acetic acid containing a trace of concd sulfuric acid at 120 deg C under nitrogen, 2-bromo-7-(2-hydroxyanilino)tropone (1a) gave 6-bromocyclohepta<1,4>benzoxazine (2a) as the main product and cyclohepta<1,4>benzoxazine, its 6,8-dibromo derivative and trace amounts of other mono, di-, and tribromo compounds.This reaction became much more complex in the presence of oxygen.A similar bromine transfer was observed for 2-bromo-7-(dimethylamino)-, 7-(2-hydroxy-5-methylanilino)-, and 7-(2-methoxyanilino)tropone although the cite of the intermolecular bromine transfer depended upon the structures of the substrates and the reaction conditions.In contrast, 2a and 2-amino-5-bromotropone derivatives were completely stable towards the strong acid.Possible reaction pathways for this bromine transfer reaction are discussed.