E-Selective Wittig Reaction

NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition state phase.

^{Click the structures and reaction black arrows in sequence to view the 3D models and animations respectively}

 

The first step of the E-selective Wittig reaction
is the production of the anti oxaphosphetane. The difference between this process and the Z-selective Wittig reaction lies in the repulsion between the aldehyde C=O and the stabilising substituent on the ylid (CO₂Me) forcing the transition state into the anti conformation, preventing the high puckering of the transition state as in the Z-selective Wittig reaction.

The second stage is the decomposition of the oxaphosphetane intermediate. After a phosphorous pseudorotation,
the intermediate decomposes via a concerted transition state to form the E-alkene and the phosphine oxide.

Back to Wittig Summary

R. Robiette, J. Richardson, V. K. Aggarwal and J. N. Harvey, J. Am. Chem. Soc., 2006, 128, 2394–2409.