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Radical trans‐Hydroboration of Alkynes with N‐Heterocyclic Carbene Boranes |
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| Authors: | Masaki Shimoi Takashi Watanabe Prof. Katsuhiro Maeda Prof. Dennis P. Curran Dr. Tsuyoshi Taniguchi |
| Affiliation: | 1. Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan;2. School of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan;3. Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan;4. Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA |
| Abstract: | Hydroboration of internal alkynes with N‐heterocyclic carbene boranes (NHC‐boranes) occurs to provide stable NHC (E)‐alkenylboranes upon thermolysis in the presence of di‐tert‐butyl peroxide. The E isomer results from an unusual trans‐hydroboration, and the E/Z selectivity is typically high (90:10 or greater). Evidence suggests that this hydroboration occurs by a radical‐chain reaction involving addition of an NHC‐boryl radical to an alkyne to give a β‐NHC‐borylalkenyl radical. Ensuing hydrogen abstraction from the starting NHC‐borane provides the product and returns the starting NHC‐boryl radical. Experiments suggest that the observed trans‐selectivity results from kinetic control in the hydrogen‐transfer reaction. |
| Keywords: | alkynes carbenes hydroboration radical reactions synthetic methods |