Selective Palladium-Catalyzed Suzuki-Miyaura Reactions of Polyhalogenated Heteroarenes

The palladium-catalyzed SuzukiMiyaura reaction of multiply halogenated, electron-rich and electron-deficient heteroarenes is one of the most reliable and environmentally friendly tools for installing a wide range of non-functionalized and functionalized carbon substituents onto heteroaromatic systems with exquisite chemo- and site-selectivity. For substrates with different halogen groups the chemoselectivity of the SuzukiMiyaura reactions has been found to be dependent on the reactivity difference between the halogens. However, the hardest achievement of selectivity in SuzukiMiyaura monocouplings involving polyhalogenated heteroarenes with identical halogen atoms has been shown to be dominated by steric and electronic effects and the presence of directing groups at positions neighbouring the reaction sites. Moreover, in the case of symmetrically substituted dihaloheteroarenes with identical halogen atoms, highly selective monocoupling reactions have often been achieved only after a careful optimization of reaction parameters including the catalyst precursor, base, solvent, and the molar ratio between electrophile and organoboron reagent. This critical review with 341 references covers developments on the chemo- and site-selective SuzukiMiyaura monocoupling reactions of polyhalogenated heteroarenes with different or identical halogen atoms. It also includes the synthesis of polysubstituted heteroarenes, not easily accessible by other means, via consecutive monocoupling reactions and/or a more synthetically valuable approach involving one-pot polycoupling reactions.