Intramolecular oxidative coupling of 3-indolylarylketones with Pd(II)-catalysis under air: convenient access to indenoindolones

A Pd-catalyzed method has been developed for the intramolecular oxidative coupling of 3-indolylarylketones under open air as terminal oxidant toward the synthesis of indeno[1,2-b]indol-10(5H)-ones. This reaction represents an intramolecular coupling with dual activation of C-H bonds for electron-deficient arenes, while such reactions are common for electron-rich arenes. Pd(II)-catalysis with pivalic acid as co-catalyst has been found to be crucial. The reaction undergoes without indole N-H-protection.