Weakly Nucleophilic Conjugate Bases of Superacids as Powerful Nucleophiles in Vinylic Bimolecular Nucleophilic Substitutions of Simple 尾-Alkylvinyl(aryl)-位3-bromanes

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• 作者：Masahito Ochiai ; Takuji Okubo ; Kazunori Miyamoto
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：March 16, 2011
• 年：2011
• 卷：133
• 期：10
• 页码：3342-3344
• 全文大小：692K
• 年卷期：v.133,no.10(March 16, 2011)
• ISSN：1520-5126

文摘

We report herein, for the first time, the stereoselective synthesis of simple (E)-尾-alkylvinyl(aryl)-位³-bromanes via a boron-位³-bromane exchange reaction and their unique bimolecular nucleophilic substitutions at the vinylic ipso carbon atom under mild conditions. Interestingly, even weakly nucleophilic anions such as conjugate bases of superacids (HBF₄, TfOH, Tf₂CH₂, Tf₃CH, Tf₂NH, etc.) function as nucleophiles toward the vinyl-位³-bromanes. For instance, the vinylic S_N2 reaction of (E)-vinyl-位³-bromanes with potassium bis(triflyl)methanide stereoselectively produced (Z)-vinyloxy oxosulfonium ylides with exclusive inversion of configuration via oxygen attack, while that with potassium bis(triflyl)imide afforded predominantly (Z)-vinyloxysulfoximines. In marked contrast, (E)-尾-alkylvinyl-位³-iodanes do not undergo the vinylic S_N2 reaction with these conjugate bases of superacids. The differences between the nucleofugalities of aryl-位³-iodanyl and aryl-位³-bromanyl groups (the latter being greater) probably play a pivotal role in these unique reactions.