Developments of Direct Synthesis and New Catalytic Reactions of Aromatic Boron Compounds

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1.Iridium-Catalyzed Aromatic C-H BorylationAromatic C-H borylation of arenes and heteroarenes using stoichiometric amounts of bis(pinacolate)diboron or pinacolborane was catalyzed by an iridium complex generated from 1/2[Ir(OMe)(COD)]_2 and 4,4'-di-tert-butyl-2,2'-bipyridine at room temperature in hexane and afforded the corresponding aromatic and heteroaromatic boron compounds in high yields with excellent regioselectivities. The reactions tolerated various functionalities such as halogen, carbonyl, and cyano groups or benzylic C-H bonds. A reaction mechanism may involve generation of a tris(boryl)iridium(III) complex by the reaction of an iridium(I) complex with bis(pinacolato)diboron or pinacolborane, oxidative addition of an aromatic C-H bond to the tris(boryl)iridium(III) complex, and reductive elimination of an aromatic boron compound. Sequential reactions, involving iridium-catalyzed aromatic C-H borylation and palladium-catalyzed cross-coupling with aromatic halides, provided a … More one-pot procedure for the synthesis of various unsymmetrical biaryls.2.Palladium-Catalyzed 1,4-Addition of Aromatic Boron Compounds to Enones1,4-Addition of aromatic boron compounds to cyclic and acyclic enones was catalyzed by dicationic palladium(II) complexes such as [Pd(dppe)(PhCN)_2](SbF_6)_2 and nitrile free complexes. A catalytic cycle involving transmetalation between an aromatic boron compound and a dicationic palladium complex to give a cationic arylpalladium(II) intermediate, insertion of an enone into a carbon-palladium bond, giving a palladium enolate, and finally hydrolysis with water to regenetrate the dicationic palladium species was proposed. Asymmetric reactions were carried out in aqueous methanol in the presence of a chiral phosphine-dicationic palladium(II) catalyst. A palladium complex of (S,S)-dipamp gave optically active β-arylketones up to 96% ee for 2-cyclohexenone and 2-cycloheptenone. A palladium-(S,S)-chiraphos complex resulted in 82-97% ee for 2-cyclopentenone and acyclic ketones. Less