Iridium catalyzed C–H borylation (CHB) offers an atom efficient synthetic route to aryl boronic esters. This methodology due to the versatility of the boronic ester products and high functional group tolerance has been well utilized and studied in the past two decades. Some of the earliest reports of metal catalyzed CHBs of arene C(sp<sup>2</sup>)–H bonds indicated that the least hindered C–H bonds were generally more reactive. This selectivity can be rationalized by the ability of the iridium active site to access arene C–H bonds. C–H bonds ortho to large groups are generally inaccessible as the group sterically repels the active iridium site. However, the traditional selectivity breaks down when multiple sterically accessible sites are available for CHB. Recently, we found by modifying ligand steric and electronic profiles it is possible to achieve regioselective CHB in aromatics where the steric differences between accessible C–H sites are small. Further, a serendipitous hydrazone ligand framework was discovered which generates a highly selective and active C–H borylation catalyst for substrates where selectivities with typical borylation protocols are poor and other C–H transformations are limited.

Hydrazone derived iridium catalysts for regioselective C–H borylations between sterically similar sites

256th National Meeting (2018)

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