Halogenation is a viable way to receive activated derivatives, which subsequently can be used for further functionalization by, e.g., transition metalcatalyzed C-C cross-coupling reactions. In this respect, electrophilic bromination of anti-benzo[1, 2-b:4,5-b']dithiophene 1 with N-bromosuccinimide (NBS) led to bromination of the -positions of the fused thiophenes in only 34% yield. The yield increased to 60% for the NBS-bromination of 4,8dihexylbenzo[1,2-b:4,5-b']dithiophene. If elemental bromine as stronger electrophile is used, 4,8-dioctyloxybenzo[1,2-b:4,5-b']dithiophene is brominated in the 2,6-positions in 99% yield. NBS-bromination of isomeric syn-benzo[1,2-b:5,4b']dithiophene 2 led to an inseparable mixture of differently brominated products. Structurally related to our dithienopyrazines, thieno [2,3-b]pyridine, thieno [3,2-b]pyridine, or thieno [2,3-b]pyrazine are throughout halogenated with elemental bromine or chlorine at the fused thiophene -position in moderate to good yields. The only information about bromination of dithienopyrazines is specified in a Chinese patent. Therein, it is claimed that NBS-bromination of anti-dithienopyrazine 5 should result in '-dibrominated 2,6-dibromodithieno[2,3-b:2′,3′-e]pyrazine in 93% yield. In our hands, NBS was too weak as a bromination agent for dithienopyrazines 5 and 6. Under various reaction conditions, even harsh ones, practically no product formation was observed. Only the use of elemental bromine in the presence of Brönsted (HBr) or Lewis acidic conditions (AlCl3), which are the typical reaction conditions for electrophilic substitutions of moderately activated aromatics such as benzene, led to controlled twofold and tetrafold bromination (Scheme 3). For the synthesis of dibrominated pyrazine 14 six equivalents of bromine in a solution of HBr in acetic acid and chloroform were used and the reaction mixture was heated under reflux for 7 days leading to 91% yield. After tedious optimization of solvents and temperature for the synthesis of tetrabrominated pyrazine 15 a great excess of bromine and aluminum trichloride (AlCl3) was used and the reaction conducted at 75 °C for one day finally leading to 92% yield. The various reaction conditions showed that the dithienopyrazine system is rather electron-deficient leading to a moderate reactivity in electrophilic substitution reactions.