para-Selective C-H Borylation of Aromatic Quaternary Ammonium and Phosphonium Salts.

Aromatic ammonium and phosphonium salts are important synthetic intermediates and multifunctional materials, but para-selective functionalization of the aromatic salts remains a challenge. Here we develop an ionic ligand based on our newly designed "biphenyl-phenanthroline" skeleton and realize the Ir-catalyzed para-selective C-H borylation of seven types of aromatic quaternary ammonium and phosphonium salts. Gram-scale transformation, late-stage elaboration for drug molecule, and diversification of borylated products demonstrate the potential utility of this reaction. The mechanistic studies and computational analysis elucidate the origin of para-selectivity.

Diversification of Aryl Sulfonyl Compounds through Ligand-Controlled meta- and para-C-H Borylation.

Aryl sulfones and aryl sulfonamides are of great importance in organic synthesis and medicinal chemistry. Although ortho-C-H functionalization of aryl sulfonyl compounds has been extensively explored, the functionalization of remote meta- and para-C-H bonds is very rare. Herein, we report a tunable meta- and para-selective C-H borylation of aryl sulfonyl compounds enabled by computationally designed ligands and iridium catalyst. This method is capable of accommodating a broad range of substrates under mild reaction conditions. Gram-scale preparation can be achieved with iridium catalyst loading as low as 0.1 mol%. As the introduced boronate group can be easily converted into many other groups, our method provides a general solution to installing functional groups at either meta- or para-position of aryl sulfones and aryl sulfonamides with good to excellent selectivity.