A series of new pyrrolo [d][1, 2, 3] thiadiazole carboxylates and 5, 6-dihydro-4H-cyclopenta [d][1, 2, 3] thiadiazoles has been synthesized via the Hurd–Mori reaction. The regioselectivity of the cyclization has been studied and trends were established to predict the cyclization direction to afford bicyclic 1, 2, 3-thiadiazoles. Effects promoting and disfavoring the reaction have also been investigated to guide the synthesis of scaffolds of ...