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The metalation of azobenzene by halogen-metal exchange typically leads to a reduction of the azo group to give hydrazine derivatives as major byproducts, instead of the desired metalated azobenzene species. In cross-coupling reactions, azobenzenes therefore usually serve as electrophiles, which greatly limits the scope of the reaction. To solve this problem, we have developed a mild and fast method to stannylate azobenzenes in high yields. This research shows that these stannylated azobenzenes can be used as nucleophilic components in Stille cross-coupling reactions with aryl bromides. The cross-coupling products were obtained in high yields ranging from 70 to 93%. With this reversal of the nucleophilic and electrophilic components, cross-coupling products are now accessible in which the aromatic rings coupled to the azobenzene bear functional groups that are sensitive to metalation.
- PALLADIUM-CATALYZED REACTION