We report herein on a catalytic system involving palladium and copper to achieve the cyclization of N-arylcyanothioformamides and the synthesis of 2-cyanobenzothiazoles. The C-H functionalization/intramolecular C-S bond formation reaction was achieved in the presence of air, using 2.0 equiv of an inorganic additive (KI). In many cases, the reaction led to a sole product regioselectively obtained in good yields, allowing the synthesis of a wide range of substituted 2-cyanobenzothiazole derivatives, providing valuable building blocks for the design of more complex heterocyclic or molecular labeling systems.
The synthesis of trifunctional isomeric benzothiazoles derived from nitroanthranilic acids and their corresponding anthranilonitrile analogues was studied. Compared to previous work, the reaction sequence afforded convenient access to hitherto undescribed 2-cyanobenzothiazoles. For further synthetic applications of these polyfunctional compounds, a hydrolysis-decarboxylation sequence was performed in acidic medium (HCl or HBr) and led to an enlarged array of relevant building blocks.
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