Synthesis of selenazoles by in situ cycloisomerization of propargyl selenoamides using oxygen-selenium exchange reaction.

Herein, we describe an approach toward selenazole preparation based on the cycloisomerization of propargyl selenoamides. The selenoamides were synthesized in situ using the Ishihara reagent with spontaneous cyclization to form the 2,5-disubstituted selenazoles. Heterocylcles 9a-j were prepared using readily available starting materials, and yields ranged from moderate to good (20-80%). Methylselenazole 9a could be transformed into a bromomethyl derivative 13 using NBS. The intermediate 13 would provide a more versatile building block for further derivatizations, e.g., the cyanide 14.