# Widely-used boronic esters as synthetically-versatile directing groups for C–H activation and hydrogen isotope exchange

## TL;DR

This paper introduces boronic esters as a new and effective tool for modifying carbon-hydrogen bonds and exchanging hydrogen isotopes in chemical reactions.

## Contribution

The first use of boronic esters as directing groups for C–H activation and hydrogen isotope exchange is demonstrated.

## Key findings

- Selective ortho-activation and functionalisation at aromatic C-sp2 centres was achieved using an iridium-based catalyst system.
- Over 30 substrates were successfully processed with excellent deuterium incorporation.
- Isotopically labelled drug molecules were prepared using the resulting boron-containing isotopologues.

## Abstract

Herein we report the first use of accessible boron-containing compounds as highly effective directing groups for C–H activation and hydrogen isotope exchange. Selective ortho-activation and functionalisation at aromatic C-sp2 centres have been achieved across an array of aryl boronic ester species using an iridium-based, NHC/phosphine catalyst system at low loadings. The process is robust, with a wide scope of over 30 substrates, and delivers excellent levels of deuterium incorporation in a selective manner. Further utilisation of the resulting boron-containing isotopologues in cross-coupling chemistry has allowed the late-stage preparation of previously less accessible site-selectively labelled structures. This strategy has been exemplified via the preparation of an isotopically-labelled, biologically-active drug molecule.

We report the first use of accessible boronic esters as effective directing groups for C–H activation and hydrogen isotope exchange. A chelated NHC/phosphine Ir catalyst system delivers selective ortho-C-sp2 activation with a range of substrates.