Synthesis of Naphthofurans by tBuOK-Catalyzed Intramolecular Anionic Cycloaddition of Unsymmetrical Bis-propargyl Ethers

• Published in: European journal of organic chemistry Vol. 2015; no. 31; pp. 6924 - 6931
• Main Authors: Grimaldi, Tamíris B., Back, Davi F., Zeni, Gilson
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-11-2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Alkynes; Cycloaddition; Ethers; Fused ring systems
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201500969

The tBuOK‐catalyzed intramolecular anionic cycloaddition of unsymmetrical bis‐propargyl ethers has been applied to the synthesis of naphthofurans. A systematic study of the cyclization system revealed that the amount of base and solvent played an essential role in this reaction. The results showed that the cyclization preceded cleanly and smoothly under mild reaction conditions, employing a catalytic amount of tBuOK as base, THF as solvent, at room temperature in a short reaction time (15 min). The reaction was regioselective, giving only naphthofurans as the unique regioisomer through an initial intramolecular 5‐endo‐dig process followed by an intramolecular 6‐endo‐dig process. The method tolerates the presence of neutral, electron‐donating and ‐withdrawing as well as heteroaryl groups in any part of the substrates. More importantly, this methodology requires only one synthetic step to prepare the conjugated polycyclic compounds.
Naphthofurans have been synthesized by tBuOK‐catalyzed intramolecular anionic cycloaddition of unsymmetrical bis‐propargyl ethers. The cyclization proceeded cleanly and smoothly under mild conditions with a catalytic amount of tBuOK as base in THF at room temperature in 15 min. The method tolerates neutral, electron‐donating and ‐withdrawing, and heteroaryl groups in any part of the substrates.