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

✍ Scribed by Tomoyuki Nasu; Tomoko Tagawa; Kimiaki Imafuku

• Book ID: 102892844
• Publisher: Journal of Heterocyclic Chemistry
• Year: 1998
• Tongue: English
• Weight: 559 KB
• Volume: 35
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570350222

✦ Synopsis

Abstract

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.