Photochemical Oxidation Specific to Distorted Aromatic Amines Providing ortho-Diketones.

A straightforward visible-light-promoted oxidation of aminohelicenes providing helical ortho-diketones is described. It is shown that the oxidation of amines proceeds via [2 + 2]-cycloaddition reaction with singlet oxygen as an oxidizer and the reaction is specific to distorted aromatic systems. The versatility of the prepared diketones and tetraketones was proven in several heterocycle-forming reactions. The observed adjustment of the physicochemical properties of original molecules is valuable for further development of functional molecules based on helicenes.