Safe Synthesis of 4,7-Dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine and Its SNAr Reactions

Abstract

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…η2-(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.

[1,2,5]Thiadiazolo[3,4-d]Pyridazine as an Internal Acceptor in the D-A-π-A Organic Sensitizers for Dye-Sensitized Solar Cells

“…Mono-adducts 3a – c and 4 were synthesized by nucleophilic aromatic substitution with appropriate amines [34] and by Suzuki cross-coupling reaction with boronic acid, following the procedures described [33] (Scheme 1).…”

“…It was found that substitution chemistry of 4,7-dibromo[1,2,5]thiadiazolo[3,4- d ]pyridazine (aromatic nucleophilic and palladium-catalysed cross-couplings) was a powerful tool for the selective formation of various mono- and bis-derivatives of strong electron-accepting heterocycles. Conditions for selective aromatic substitution of one bromine atom by oxygen and nitrogen nucleophiles [34], as well as by Suzuki-Miyaura coupling by arylboronic acids, were found. These results have driven us to the conclusion that this might be a good basis for the synthesis of dyes for DSSCs.…”

3,6-Dibromopyridazine-4,5-diamine

“…Recently, we have shown that 4,7-dibromo [1,2,5]thiadiazolo [3,4-d]pyridazine 1 can be safely and efficiently prepared from the commercial diaminomaleonitrile [12]. Herein, we examined the reduction of this compound (Scheme 1).…”

“…During our investigation of the nucleophilic substitution in 4,7-dibromo [1,2,5]thiadiazolo[3,4-d]pyridazine 1 by alkoxide anions we observed the formation of the new compound as a side product which was proved by mass-spectrometry to be 3,6-dibromopyridazine-4,5-diamine 2. We showed that the treatment of 1 with sodium methoxide in MeOH led to the formation of bis(methoxy) derivative 3 [12] with a traces of diamine 2 (Entry 3). To develop the synthetic approach to the target compound 2 we investigated this reaction in other solvents.…”

“…This method may open new possibilities for reductive cleavage of the 1,2,5-thiadiazole ring fused with electron-accepting rings and containing functional derivatives. [1,2,5]thiadiazolo[3,4-d]pyridazine 1 was prepared according to the published method [12]. Melting point was determined on a Kofler hot-stage apparatus and is uncorrected.…”