SpiroBpy-BPin: Ligand for meta-Selective Catalytic C-H Borylation

Since the development of the C-H borylation reaction, which allows the introduction of a boron functional group directly onto the C-H of an arene, the variety of available borylated arenes has increased dramatically. In the early C-H borylation reactions, boron was introduced at sterically vacant positions of substituted arenes. ortho-Selective C-H borylation reactions using arenes having directing substituents, and para-selective borylation reactions using high sterically hindered ligands have been developed. However, it has not been easy to discriminate meta- and para-positions in the C-H borylation reaction for simple substituted arenes. Therefore, there is a need to develop ligands that exhibit meta-selectivity for a wide range of arenes.
SpiroBpy-Bpin (1) is a catalytic C-H borylation ligand that exhibits excellent meta-selectivity.^1,2) The Bpin substituent on the spirobipyridine moiety of 1 plays the role of a roof, and the meta-position of hydrogen of the substrate preferentially approaches the metal center, resulting in meta-selectivity. For example, in the C-H borylation of tert-butylbenzene using HBpin, [IrOMe(cod)]₂ and 1, the meta-selectivity reaches m:p = 23:1. A meta-selectivity of m:p = 5.0:1 is achieved even when the substrate is toluene. Thus, 1 shows excellent meta-selectivity for various substituted arenes, and the application of meta-borylated arenes is expected in the future.

References

• 1) Remote steric control for undirected meta-selective C-H activation of arenes
  • B. Ramadoss, Y. Jin, S. Asako, L. Ilies, Science 2022, 375, 658.
• 2) Remote Steric Control for Undirected meta-Selective C–H Activation of Arenes
  • B, Ramadoss, Y. Jin, S. Asako, L. Ilies, Synform 2022, 06, A92.

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