Collect. Czech. Chem. Commun. 1986, 51, 2839-2847

Photocyclization of N-(3-chloro-2-benzo[b]thienocarbonyl)-N'-monosubstituted thioureas

Peter Kutschy, Ján Imrich, Juraj Bernát, Pavol Kristian, Oľga Hritzová and Thomas Schöffmann

Department of Organic Chemistry and Biochemistry, faculty of Natural Sciences, P. J. Šafárik University, 041 67 Košice


N-(3-Chloro-2-benzo[b]thienocarbonyl)-N'-monosubstituted thioureas, when irradiated with a high-pressure mercury discharge lamp through a pyrex or quartz filter, give the corresponding benzothienothiazine derivatives in lower yields than the analogous N',N'-disubstituted thioureas. The reactivity lowering of the N'-monosubstituted thioureas is ascribed to the intramolecular hydrogen bond C=O...H-N due to which these compounds in their ground states exist in the six-membered cyclic conformation unfavourable for the cyclization. The photolysis of N'-phenylthiourea results - due to a stronger hydrogen bond - in splitting of the molecule to give 3-chlorobenzo[b]thiophene-2-carboxamide and phenyl isothiocyanate.