Selenium‐Containing Heterocycles from Isoselenocyanates: Synthesis of 1,3‐Selenazoles from N‐Phenylimidoyl Isoselenocyanates

The reaction of N‐phenylbenzamides 5 with excess SOCl₂ under reflux gave N‐phenylbenzimidoyl chlorides 6 , which, on treatment with KSeCN in acetone, yielded imidoyl isoselenocyanates of type 2 . These products, obtained in almost quantitative yield, were stable in the crystalline state. They were transformed into selenourea derivatives 7 by the reaction with NH₃, or primary or secondary amines. In acetone at room temperature, 7 reacted with activated bromomethylene compounds such as 2‐bromoacetates, acetamides, and acetonitriles, as well as phenacyl bromides and 4‐cyanobenzyl bromide to to give 1,3‐selenazol‐2‐amines of type 9 (Scheme 2). A reaction mechanism via alkylation of the Se‐atom of 7 , followed by ring closure and elimination of aniline, is most likely (cf. Scheme 7). In the case of selenourea derivatives 7d and 7l with an unsubstituted NH₂ group, an alternative ring closure via elimination of H₂O led to 1,3‐selenazoles 10a and 10b , respectively (Schemes 4 and 7). On treatment with NaOH, ethyl 1,3‐selenazole‐5‐carboxylates 9l and 9s were saponified and decarboxylated to give the corresponding 5‐unsubstituted 1,3‐selenazoles 12a and 12b (Scheme 6). The molecular structures of selenourea 7f and the 1,3‐selenazoles 9c and 9d have been established by X‐ray crystallography (Figs. 1 and 3).