Tributylphosphine mediation

A few functionalized allylic phosphonium ylides are generated by the nucleophilic attack of phosphines on certain allenoates followed by a set of proton transfers. Taking advantage of this chemistry, He et al. have developed a triarylphosphine mediated olefination of aldehydes with y-substituted allenoates to afford trisubstituted conjugated dienes in moderate to excellent yields and with high E selectivity (Scheme 25) [119]. Similarly, the reaction of aldehydes with a-substimted allenoates has been developed in the presence of tributylphosphine to afford polysubstimted conjugated dienes (Scheme 26) [120, 121]. 

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