Selective ortho-C–H Activation in Arenes without Functional Groups

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Abstract
Aromatic C-H activation in alkylarenes is a key step for the synthesis of functionalized organic molecules from simple hydrocarbon precursors. Known examples of such C-H activations often yield mixtures of products resulting from activation of the least hindered C-H bonds. Here we report highly selective ortho-C-H activation in alkylarenes by simple iridium complexes. We demonstrate that the capacity of the alkyl substituent to override the typical preference of metal-mediated C-H activation for the least hindered aromatic C-H bonds results from transient insertion of iridium into the benzylic C-H bond. This enables fast iridium insertion into the ortho-C-H bond, followed by regeneration of the benzylic C-H bond by reductive elimination. Bulkier alkyl substituents increase the ortho selectivity. The described chemistry represents a conceptually new alternative to existing approaches for aromatic C-H bond activation.
Funding Information
  • Engineering and Physical Sciences Research Council (EP/L000075/1)
  • Leverhulme Trust (RPG-2018-406)
  • Royal Society of Chemistry (E21-7333927136)
  • American Chemical Society Petroleum Research Fund (58885-ND7)

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