Base‐Mediated Hydroamination of Propargylamine: A Regioselective Intramolecular 5‐exo‐dig Cycloisomerization en Route to Imidazole‐2‐thione.

An intramolecular transition-metal-free base-mediated hydroamination of propargylamine with isothiocyanates has been achieved. This atom-economical, regioselective intramolecular 5-exo-dig cycloisomerization was utilized for the one-pot synthesis of diversely substituted imidazole-2-thione and spiro-cyclic imidazolidine-2-thione. The reaction goes to completion at room temperature via propargylthiourea and 65–97% isolated yields were obtained.