Investigation of the regioselectivity of the Hurd–Mori reaction for the formation of bicyclic 1,2,3-thiadiazoles

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 this type.