The concerted addition of HBr to aryl alkynes; orthogonal pi bond selectivity

In a weakly acidic solution, the addition of HBr to 1-phenylprop-1-yne produces predominantly the anti-Markovnikov product. In this paper, we consider five possible explanations for this behavior and conclude that the concerted addition is occurring on the acetylenic pi bond orthogonal to the extend...

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Published inOrganic & biomolecular chemistry Vol. 1; no. 12; pp. 2152 - 2156
Main Authors Weiss, Hilton M, Touchette, Kim M, Angell, Sarah, Khan, Jihan
Format Journal Article
LanguageEnglish
Published England 21.06.2003
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Summary:In a weakly acidic solution, the addition of HBr to 1-phenylprop-1-yne produces predominantly the anti-Markovnikov product. In this paper, we consider five possible explanations for this behavior and conclude that the concerted addition is occurring on the acetylenic pi bond orthogonal to the extended aromatic pi system. The electronic effect of the distal methyl group and the steric hindrance of the coplanar phenyl ring combine to promote bromide attack at the beta carbon. Attack on this pi bond is insensitive to the electronic effect of meta and para substituents on the ring but is very (sterically) sensitive toward all ortho substituents.
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ISSN:1477-0520
DOI:10.1039/b300045a