New substituted methyl thieno[3,4-c]cinnoline-3-carboxylate compounds were synthesized from the corresponding methyl 3-aminothiophene-2-carboxylate precursors by a new route using a modified Sandmeyer reaction. Under proper conditions, Sandmeyer reaction led to the formation of thieno[3,4-c] cinnoline compounds by a regioselective intramolecular cyclization, instead of the expected substitution of the amino group by a bromine atom