Synthesis and reactions of 1,3‐dicarbonyl‐substituted troponoids: Conversion to tropolones having an isoxazole or a pyrazole ring

3‐Acetyltropolone ( 1 ) was treated with diethyl oxalate in the presence of sodium ethoxide to afford 3‐(2‐ethoxalyl‐1‐oxoethyl)tropolone ( 2 ) as a minor product and its cyclized 2‐ethoxycarbonyl‐4,9‐dihydrocyclohetpa[ b ]pyran‐4,9‐dione ( 3 ) as the major one. The former was readily converted to the latter. Then, as a stable synthon bearing a 1,3‐dicarbonyl group, 2‐(2‐ethoxalyl‐1‐oxoethyl)‐7‐methylaminotropone ( 5 ) was prepared. The reactions of compound 5 with hydroxylamine, hydrazine, and methylhydrazine were carried out to give troponoids possessing an isoxazole or a pyrazole ring. The parent compounds, 3‐(3‐pyrazolyl)tropolone ( 13 ) and 3‐(1‐methylpyrazol‐3‐yl)tropolone ( 21 ), were obtained via hydrolysis and decarboxylation. Similarly, 2‐ethoxycarbonyl‐4,9‐dihydrocyclohepta[ b ]pyran‐4,9‐dione ( 3 ) reacted with hydroxylamine, hydrazine, and methylhydrazine to yield troponoids possessing a heterocyclic ring.