In a high yield photoreaction (90–99 %), enyne–carbodiimides (X=N) cyclize to indoloquinolines within a few minutes (see scheme). Analogously, enyne–ketenimines (X=CAr) photocyclize to benzocarbazoles, which paves the way to a simple synthesis of certain photoactive prodrugs.

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Both benzocarbazoles and quinolines can be synthesized from enyne ketenimines 1 generated in situ via biradical intermediates (see reaction below). Which of the heterocyclic ring systems is formed depends on the choice of the substituent R at the alkyne terminus.