Copper-catalyzed construction of eight-membered rings via oxidative ring expansion and intermolecular cyclization sequencing of indoles with amidines: efficient synthesis of benzo[1,3,5]triazocin-6(5H)-ones

Novel and efficient synthesis of eight-membered nitrogen heterocycles in one pot by copper-catalyzed oxidative ring expansion and intermolecular cyclization sequencing of indoles with amidines has been described. This protocol features easily available substrates and high step-economy. More importantly, dioxygen as the most ideal oxidant was employed under mild reaction conditions. A variety of valuable benzo[1,3,5]triazocin-6(5H)-one derivatives bearing functional groups were assembled in middle to good yields.