Transition-metal-free base catalyzed intramolecular cyclization of 2-ynylphenols for efficient and facile synthesis of 2-substituted benzo[ b]furans

A transition-metal-free base catalyzed intramolecular cyclization of 2-ynylphenols was developed for the facile synthesis of 2-substituted benzo[b]furans. Various 2-aryl and 2-alkyl substituted benzo[b]furans can be obtained with good to excellent yields using readily available Cs₂CO₃ as the catalyst under mild reaction conditions. The broad substrates scope and the typical maintenance of vigorous efficiency on gram scale make this protocol a potentially practical method to synthesize 2-substituted benzo[b]furans derivatives.