Studies on the mechanism of the Cadogan–Sundberg indole synthesis

The Cadogan–Sundberg indole synthesis produces two major products from the treatment of 2-nitrostilbenes with triethyl phosphite, which are the 2-arylindoles and the corresponding 2-aryl-N-ethoxyindoles. We were interested in determining the origin of the oxygen atom in the 2-aryl-N-ethoxyindoles. In this study, we verify that this oxygen atom originates from the nitro group and not from the triethyl phosphite.