Synthesis and reactions of 3‐carboxytropolone. Conversion to heterocycle‐fused troponoid compounds

The haloform reaction of 3‐acetyltropolone ( 1 ) afforded 3‐carboxytropolone ( 2 ) which was treated with diazomethane to give 2‐methoxy‐3‐methoxycarbonyltropone (3a) and 2‐methoxy‐7‐methoxycarbonyltropone (3b). The tropolone 2 reacted with hydrazine to afford 2‐hydrazino‐3‐hydrazinocarbonyltropone ( 10 ) or 2‐hydrazinotropone ( 11 ), depending on the reaction time. The reaction of 2 with phenylhydrazine produced 3‐hydroxy‐1‐phenyl‐1,8‐dihydrocycloheptapyrazol‐8‐one (14). The treatment of 2‐methoxy‐3‐methoxycarbonyltropone (3a) with hydrazine or phenylhydrazine gave cyclization products 12 and 15 , respectively. The reaction of 2‐methoxy‐7‐methoxycarbonyltropone (3b) with hydrazine, phenylhydrazine, or methylhydrazine gave 2‐hydrazino‐ ( 13 ), 2‐(2‐phenylhydrazino)‐ ( 16 ), and 2‐(2‐methylhydrazino)‐7‐methoxycarbonyltropone ( 17 ), respectively.