Synthesis of Non-Symmetric Azoarenes by Palladium-Catalyzed Cross-Coupling of Silicon-Masked Diazenyl Anions and (Hetero) Aryl Halides

摘要

The photoswitchable motif of azobenzenes is of great importance across the life and materials sciences. This maintains a constant demand for their efficient synthesis, especially that of non-symmetric derivatives. We disclose here a general strategy for their synthesis through an unprecedented C(sp~2)-N(sp~2) cross-coupling where functionalized aryl-substituted diazenes masked with a silyl group are employed as diazenyl pronucleophiles. These equivalents of fragile diazenyl anions couple with a diverse set of (hetero)aryl bromides under palladium catalysis with no loss of dinitrogen. The competing denitrogenative biaryl formation is fully suppressed. The reaction requires only a minimal excess, that is 1.2 equivalents, of the diazenyl component. By this, a broad range of azoarenes decorated with two electron-rich/deficient aryl groups can be accessed in a predictable way with superb functional-group tolerance.