Iron-Catalyzed Synthesis of Polysubstituted Benzofurans

Significance

The iron-catalyzed oxidative ­Pechmann condensation of phenols 1 with β-keto esters 2 to give polysubstituted benzofurans 3 is reported. Extensive optimization showed that the presence of a proton source such as water is ­crucial to obtain high yields of the desired products. Electron-rich phenols bearing ortho or para substituents were well tolerated in the reaction. In contrast, no product was obtained from phenols bearing strong EWGs (R^¹ = NO₂, Ac). A tentative mechanism involving first oxidative coupling to give 4 followed by condensation is proposed based on the independent synthesis of the possible intermediates.