The selectivity of catalytic C-H borylation of arenes has usually been ruled by steric factors. Generally, functionalization occurs at the least sterically hindered site, not at the most electron-rich or electron-poor site. While this can impart high selectivity for 1,3-substituted benzenes, the selective functionalization of 1,2- and 1,4-subsituted substrates is much more challenging. While ortho-functionalizations of arenes with directing groups are well documented (e.g. ortholithiations and Pd mediated functionalizations), direct functionalizations of phenols often requires installation of a directing group that is subsequently removed. In the case of C-H borylation, direct ortho-borylation of C-H bonds in phenols would provide milder synthetic approach. We have shown that pinacolborane could be employed as the traceless protecting and directing group for the iridium-catalyzed ortho-selective borylation of phenols. Remarkably, the selectivities are dramatically improved over those of methyl aryl ethers. Our results will be discussed in detail.

Pinacolborane: A traceless protecting and directing group for Ir-catalyzed ortho-selective borylation of phenols

248th National Meeting (2014)

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