Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 144, Issue 51, Pages 23286-23291Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.2c12151
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Funding
- National Natural Science Foundation of China [21871051, 22071027, 22173021, 22271050]
- Shanghai Science and Technology Committee [19DZ2270100]
- Fudan University
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This study presents the development of a metal-free catalyst for the borylation of unactivated arenes. The catalyst enables the borylation of sterically encumbered positions and achieves para-selective borylation of phenols, both of which are challenging tasks for transition-metal systems. Mechanistic studies support a synergistic activation mechanism involving the catalyst and the borylation reagent.
Non-metal-catalyzed C-H borylation of arenes represents a sustainable and environment-friendly approach for the functionalization of arenes. Despite its promise as an alternative to traditional transition-metal systems, its substrate scope is generally limited to electron-rich arenes, thus hindering its application in organic synthesis. Herein, we report the development of a borenium-ion catalyst which can borylate unactivated arenes under ambient conditions with 4-chlorocatecholborane (HBcatCl) as borylation reagent. This metal-free catalytic system is suitable for the borylation of C-H bonds in sterically encumbered positions, which has been a challenging task for transition-metal systems. Additionally, this catalytic system allows para-selective one-pot borylation of phenols, which has not been achieved by using transition-metal systems. Our mechanistic investigations and computational studies support a synergistic activation of the H-BcatCl bond by the arene substrate and the borenium-ion catalyst. This generates a Wheland intermediate and a neutral hydroborane species and is followed by deprotonation of the Wheland intermediate with the hydroborane species. The latter step of C-H bond cleavage is likely the rate-limiting step.
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