Bromination and Protodebromination of 3-Phenanthrols at the 4-Position

Abstract

The reaction pathways in the bromination and protodebromination of 3-phenanthrols have been studied.When 3-phenanthrol (1) was treated with bromine in carbon tetrachloride at 0°C in the presence or the absence of anhydrous sodium carbonate, 4-bromo-3-phenanthrol (2) or 9-bromo-3-phenanthrol (3) was obtained, respectively. In contact with dry hydrogen bromide, (2) was readily isomerized into (3). When this isomerzation reaction of (2) was conducted in the presence of 2-phenanthrol (4), 1-bromo-2-phenanthrol (5) was also obtained.These facts suggest the following reaction scheme.(2)+HBr _??_ (1)+Br2→ (3)+HBr(4) →→ (5)+HBr(2) and 2, 4, 9-tribromo-3-phenanthrol (6) were also prepared from (1) and 2, 9-dibromo-3-phenanthrol (7), respectively, by the reaction with N-bromo-tert-butylamine. When heated with hydrogen bromide, (6) was debrominated to give (7) and free bromine.The structures of (2) and (6) were determined by converting into respective known compounds.