In this paper, a simple and practical synthesis of benzo[e]benzo[4,5]imidazo[1,2-c][1,3]thiazin-6-imine tetracyclic heterocycles via a CuI nanoparticle-catalyzed intramolecular C(sp²)–S coupling reaction is presented. This strategy provides a straightforward method for synthesizing analogs of the anti-HIV drug 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine (PD 404182). The reaction rate and yield were increased by employing CuI nanoparticles.