Synthesis and reactions of halo‐, nitro‐, and arylazo‐substituted 3‐aminotropolones. Formation of 8 H ‐cyclohept[ d ]oxazol‐8‐one derivatives

3‐Acetamidotropolone ( 1a ) reacted with bromine and fuming nitric acid to afford respectively 3‐acetamido‐7‐bromo‐ ( 1b ) and ‐5,7‐dibromotropolone ( 1c ) and 3‐acetamido‐5‐nitrotropolone ( 1d ). Azo‐coupling reaction of 1a gave 3‐acetamido‐5‐(4‐methylphenylazo)tropolone ( 1f ). Bromination of 1d and 1f gave 7‐bromo‐substituted compounds 1e and 1g , respectively. The compounds 1b‐g were hydrolyzed to afford 3‐aminotropolones 4b‐g , which reacted with triethyl orthoformate to give the corresponding 8 H ‐cyclohept[ d ]oxazol‐8‐ones 5b‐g . Heating of 3‐acetamidotropolones 1a‐d with polyphosphoric acid gave 2‐methyl‐8 H ‐cyclohept[ d ]oxazol‐8‐ones 6a‐d .