Boron Lewis Acid‐Catalyzed Hydroboration of Alkenes with Pinacolborane: BArF3 Does What B(C6F5)3 Cannot Do!
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Authors: | Dr Qin Yin Dr Hendrik F T Klare Prof Dr Martin Oestreich |
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Institution: | 1. http://www.organometallics.tu‐berlin.de;2. Institut für Chemie, Technische Universit?t Berlin, Berlin, Germany |
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Abstract: | The transition‐metal‐free hydroboration of various alkenes with pinacolborane (HBpin) initiated by tris3,5‐bis(trifluoromethyl)phenyl]borane (BArF3) is reported. The choice of the boron Lewis acid is crucial as the more prominent boron Lewis acid tris(pentafluorophenyl)borane (B(C6F5)3) is reluctant to react. Unlike B(C6F5)3, BArF3 is found to engage in substituent redistribution with HBpin, resulting in the formation of ArFBpin and the electron‐deficient diboranes H2BArF]2 and (ArF)(H)B(μ‐H)2BArF2]. These in situ‐generated hydroboranes undergo regioselective hydroboration of styrene derivatives as well as aliphatic alkenes with cis diastereoselectivity. Another ligand metathesis of these adducts with HBpin subsequently affords the corresponding HBpin‐derived anti‐Markovnikov adducts. The reactive hydroboranes are regenerated in this step, thereby closing the catalytic cycle. |
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Keywords: | alkenes boranes homogeneous catalysis hydroboration Lewis acids |
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