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Dicationic phosphonium salts: Lewis acid initiators for the Mukaiyama-aldol reaction

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Abstract

Two strategies were used to prepare dicationic phosphonium cations. The first method consists of the reaction of 1-chlorocyclopropenium salts with phosphines to obtain cyclopropenium-substituted phosphonium salts 10a–f[BF4]. Anion exchange was performed to access the corresponding [B(C6F5)4] analogues 10a–f[B(C6F5)4], which showed much higher solubility in organic solvents. In addition, we developed a synthesis of dicationic phosphonium salts containing 2-, 3-, or 4-methylpyridinium substituents 11a–c[TfO], which were converted as well to their [B(C6F5)4] analogues 11a–c[B(C6F5)4]. Finally, the phenoxy-substituted phosphonium salt 12[B(C6F5)4] was also prepared. All salts demonstrated remarkable stability in air as compared with their fluorinated analogues. The Lewis acidity of these salts was evaluated by means of theoretical calculations and finally, they were shown to be effective in initiating the Mukaiyama-aldol reaction.

Graphical abstract: Dicationic phosphonium salts: Lewis acid initiators for the Mukaiyama-aldol reaction

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Publication details

The article was received on 29 Aug 2017, accepted on 02 Nov 2017 and first published on 14 Nov 2017


Article type: Paper
DOI: 10.1039/C7DT03197A
Citation: Dalton Trans., 2017, Advance Article
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    Dicationic phosphonium salts: Lewis acid initiators for the Mukaiyama-aldol reaction

    A. G. Barrado, J. M. Bayne, T. C. Johnstone, C. W. Lehmann, D. W. Stephan and M. Alcarazo, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT03197A

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