Safe Synthesis of 4,7-Dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine and Its S(N)Ar Reactions

A safe and efficient synthesis of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine from the commercial diaminomaleonitrile is reported. Conditions for selective aromatic nucleophilic substitution of one or two bromine atoms by oxygen and nitrogen nucleophiles are found, whereas thiols formed the bis-derivatives only. Buchwald-Hartwig or Ullmann techniques are successful for incorporation of a weak nitrogen base, such as carbazole, into the [1,2,5]thiadiazolo[3,4-d]pyridazine core. The formation of rather stable S…η(2)-(N=N) bound chains in 4,7-bis(alkylthio)-[1,2,5]thiadiazolo[3,4-d]pyridines makes these compounds promising for the design of liquid crystals.