One‐Pot Transformation Strategy of o‐Hydroxyphenyl Propargylamines for Modular Access to 3‐Functionalized Benzofurans

Abstract

A one‐pot strategy to C3‐functioanlized benzofurans is achieved from o‐hydroxyphenyl propargylamines (o‐HPPAs). 3‐Aminobenzofurans were obtained in 64‐96% yields through the cascade alkyne‐allene tautomerization and 5‐exo‐dig annulation of o‐HPPAs in the presence of KOH/NaOtBu as the fruitful base combination. Moreover, with bench‐top benzenesulfinates and diphenylphosphine oxide as nucleophiles, a one‐pot protocol derivatives was also demonstrated through a cascade 1,4‐conjugate addition/5‐exo‐dig annulation/aromatization process. Additionally, the gram‐scale synthesis and further transformation into other valuable functionalized benzofurans were conducted to show the potential in organic synthesis of these developed synthetic approaches.