Irradiation of N-thioaroylureas and N-thioaroylthioureas gave imidazolidinones and imidazolidinethiones, respectively both via intramolecular hydrogen abstraction by the thioaroyl groups; the photoproducts were easily converted to the imidazolones and imidazolthiones on treatment with trifluoroacetic acid.
N′,N′-Dibenzyl and N′,N′-diisopropyl-N-aroylureas undergo cyclization on irradiation to give the corresponding imidazolidin-2-ones via intramolecular hydrogen abstraction by the aroyl carbonyl group.