Synthesis of Pyridyl and Pyridazyl Boropinacolates by Ir-Catalyzed C-H activation

Significance

Ir-catalyzed borylation of 2-phenyl- or 2-pyridylpyridines by direct C-H activation is reported. Interesting C-5 and C-6 regioselectivity is observed depending on OMe and t-Bu substitution, respectively. In contrast, under the same conditions, 2-phenylpyridine leads to a 1:1 mixture of the 4- and 5-pyridyl pinacol boranes presumably owing to a steric effect. The requirement for an α-substituent (i.e., the other α-pyridyl) to prevent catalyst poisoning by the nitrogen lone pair is proposed. The structures of products were determined by single-crystal X-ray diffraction and Suzuki cross-couplings were carried out to give corresponding phenyl-substituted bipyridyl derivatives. A similar sequence on 2,3-dimethylpyrazine gave the corresponding 5-thienylpyrazine in 34% yield.