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Synthesis of Isoquinoline-Containing 5,6-Dicyano-2,1,3-Benzothiadiazoles: Unusual Heterocyclization into Dibenzo-1,6-Naphthyridine Framework
An efficient access to novel families of cyano-containing polyheteroaromatic D- A molecules with extended π-conjugation, including dibenzo[c,h][1,6]naphthyridine derivatives, has been elaborated. The synthetic strategy is based on the sequence of metal-catalyzed annulation and cross-coupling reactions starting from available 4-ethynyl-5,6-difluoro-7-(pmethoxyphenyl)- 2,1,3-benzothiadiazole to get a new series of isoquinoline-linked BTD-based D- A compounds, which further undergo a selective cyanation to afford the corresponding mono-CN- or di-CN-BTD derivatives depending on the reaction conditions. In course of the investigation of cyanation process, a new type of intramolecular heterocyclization included the transformation of the benzothiadiazole core into hardly accessible dibenzo[c,h][1,6]naphthyridine framework has been unexpectedly discovered. The protocols developed tolerate a wide range of donor blocks such as diphenylamine, carbazole, dibenzoazepine and dihydroacridine.