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 NH,, 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 71 with an unsubstituted NH? group, an alternative ring closure via elimination of H2O led to 19-selenazoles 10a and 10b, respectively (Schemes 4 and 7). On treatment with NaOH, ethyl 1,3-selenazole-5-carboxylates 91 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. I and 3).