Stereoselective Wittig Reaction-Overview

()

‘Click’ the different stages to view 3D models of the Z- and E-stereoselective examples of the Wittig reaction mechanism:

Z-Selective Wittig Reaction

Stage 1:Unstabilised Ylid Formation

The nature of the selectivity of the Wittig reaction is chosen by the type of phosphonium ylid used. The Z-selective reaction is favoured with an unstabilised phosphonium ylid as in the example below.

Stage 2: Z-Selective Wittig Reaction

The Z-stereoselective Wittig reaction consists of a stereoselective first step forming the syn oxaphosphetane. This is then followed by a stereospecific elimination of this intermediate to form the Z alkene.

E-Selective Wittig Reaction

Stage 1: The E-selective Wittig reaction requires stabilised ylids whereby the substituents on the carbon are conjugating or anion stabilising, such as a carbonyl group. The mechanism for the formation of this ylid has been omitted here as these molecules are stable enough to be considered starting materials.

Stage 2: E-Selective Wittig Reaction

Due to the stabilisation that the conjugating or anion stabilising group supplies to the phosphonium ylid the intermediate produced is the anti oxaphosphetane. This then undergoes a stereospecific second step in order to produce the E alkene.

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

 

 

How useful was this page?

Click on a star to rate it!

Average rating / 5. Vote count:

No votes so far! Be the first to rate this page.

As you found this page useful...

Follow us on social media!

We are sorry that this page was not useful for you!

Let us improve this page!

Tell us how we can improve this page (in your own language if you prefer)? If you would like a response, please include your email address e.g. [email protected]

Provided by the