Polarity reversal catalysis in radical reductions of halides by N-heterocyclic carbene boranes |
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Authors: | Pan Xiangcheng Lacôte Emmanuel Lalevée Jacques Curran Dennis P |
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Institution: | Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States. |
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Abstract: | Otherwise sluggish or completely ineffective radical reductions of alkyl and aryl halides by N-heterocyclic carbene boranes (NHC-boranes) are catalyzed by thiols. Reductions and reductive cyclizations with readily available 1,3-dimethylimidazol-2-ylidene borane and a water-soluble triazole relative are catalyzed by thiophenol and tert-dodecanethiol C(9)H(19)C(CH(3))(2)SH]. Rate constants for reaction of the phenylthiyl (PhS?) radical with two NHC-boranes have been measured to be ~10(8) M(-1) s(-1) by laser flash photolysis experiments. An analysis of the available evidence suggests the operation of polarity reversal catalysis. |
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