Unsaturated bisphosphonium salts

Unsaturated bisphosphonium salts have been also studied182,763,764. On mercury cathodes, in unbuffered or acidic aqueous-organic media, the electrochemical reduction was shown to be controlled by the ylide character of the first-formed radicals, which then exclusively induced a heterolytic P—C bond breaking on the unsaturated bridge182 (Scheme 10). 

Wittig reaction.1 Aldehydes when refluxed with the bisphosphonium salt (1) in a benzene-water solvent containing sodium hydroxide are converted into a,j3-unsaturated... 

Prior to the studies discussed above, Mukaiyama et al. explored in 1989 the behavior of phosphonium salts as Lewis acid catalysts. It was shown that the aldol-type reaction of aldehydes or acetals with several nucleophiles and the Michael reaction of a,P-unsaturated ketones or acetals with silyl nucleophiles gave the products in good yields with a phosphonium salt catalyst [71]. In a similar study by the same group a bisphosphonium salts (Scheme 16.25) was used as a catalyst for the synthesis of P-aminoesters [72]. High yields of up to 98% were reached in the reaction of N-benzylidene-aniline with the ketene sdyl acetal of methyl isobutyrate. The bisphosphonium salt was found in this reaction to be a better Lewis acid catalyst than TiCl, and SnCl, which were deactivated by the resulting amines. 

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