Iridium-catalyzed C-H borylation of CF3-substituted pyridines will be presented. The boronic ester group can be installed on the alpha, beta, or gamma position of pyridine by appropriate substitution pattern. Sterically governed regioselectivity provides convenient access to variety of CF3-substituted pyridylboronic esters. These catalytic C-H borylation reactions were carried out neat without the use of any solvent. Several functional groups such as halo, ester, alkoxy, amino etc. are compatible with this methodology. These pyridylboronic esters are amenable to column chromatography and the products were isolated in good to excellent yields. Alpha-borylated pyridines, although isolated in good yields, do not have long shelf life. The boronic esters derivatives of these CF3-substituted pyridines can serve as useful precursors in the synthetic regime. Iridium-catalyzed C-H borylation has also been applied to various unsymmetrical 2,6-di-substituted pyridines and the corresponding 4-borylated pyridines were isolated in good to excellent yields. Excellent meta regioselectivities for sterically governed borylation were observed for several substituents. However, erosion in meta selectivity was observed for alkoxy/fluoroalkoxy and cyano substituted 2,6-disubstituted pyridines which is in contrast to excellent meta selectivities generally observed for these substituents in aromatic C-H borylation.

Iridium-catalyzed C-H borylation of substituted pyridines

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