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‐(p‐methoxyphenyl)‐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.