Triarylmethylphosphonium halides

Wittig-Smiles reaction.l The reaction of a triarylmethylphosphonium halide and a base with an a-keto dicarboxylic acid halide imide such as 1 results in a Wittig reaction followed by a Smiles rearrangement to provide a pyrrolidine dione... 

With strong bases it is also possible to remove a proton from the methyl group of triarylmethylphosphonium halides, trimethylsulfonium iodide, or trimethylsulfoxonium iodide (Figure 9.1). Here, too, species are produced that are betaines of the ylide type. 

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