Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15208, United States.
J Am Chem Soc. 2020 Apr 1;142(13):6261-6267. doi: 10.1021/jacs.0c00490. Epub 2020 Mar 23.
Reactions of N-heterocyclic carbene boranes (NHC-boranes) with electron-poor aromatic rings under photoredox conditions provide dearomatized 3-NHC-boryl-1,5-cycohexadienes, which are formally products of 1,4-hydroboration reactions. When regioisomers are possible, the more crowded (doubly ortho-substituted) product is formed preferably or exclusively. The mechanism may involve oxidation of the NHC-borane to an NHC-boryl radical, reduction of the electron-poor aromatic ring to a radical anion, coupling of the radical and the radical anion to give a cyclohexadienyl anion, and finally regioselective protonation.
氮杂环卡宾硼烷（NHC-boranes）与缺电子芳环在光氧化还原条件下的反应提供去芳构化的 3-NHC-硼基-1,5-环己二烯，其形式上是 1,4-氢硼化反应的产物。当存在区域异构体时，更拥挤的（双邻位取代）产物优先或排他地形成。该机理可能涉及 NHC-硼烷被氧化为 NHC-硼基自由基，缺电子芳环被还原为自由基阴离子，自由基和自由基阴离子偶联生成环己二烯基阴离子，最后进行区域选择性质子化。
