Other Sigmatropic Shifts

Base catalyzed reactions of allylic ethers and amines may take different paths depending on substitution and conditions. Often [2,3]-sigmatropic shifts occur in preference to others. The example shown below is illustrative. Both the [2,3]-shift and the minor [1,4]-shift are regio and stereospecific, suggesting a structured transition state for each.

[2,3]-Sigmatropic shifts of this kind are commonly called [2,3]-Wittig rearrangements. A general example involving diallyl ethers is shown in the following diagram. By clicking on the diagram the cyclic chair-like mechanism proposed to account for the stereospecificity of this reaction will be displayed. A second click on the diagram will show two additional examples which demonstrate the synthetic utility of the reaction.