The key difference between Wittig reaction and Wittig rearrangement is that Wittig reaction forms an alkene as the final product while Wittig rearrangement forms an alcohol or the corresponding ketone as the final product.
Wittig reaction and Wittig rearrangement are very important in organic chemistry for synthetic processes. A rearrangement occurs after a reaction to form the most stable final product.
CONTENTS
1. Overview and Key Difference
2. What is Wittig Reaction
3. What is Wittig Rearrangement
4. Side by Side Comparison – Wittig Reaction vs Wittig Rearrangement in Tabular Form
5. Summary
What is Wittig Reaction?
In organic chemistry, Wittig reaction is a type of coupling reaction in which aldehydes or ketones react with phosphonium ylides, forming an alkene. We can name this reaction as Wittig olefination reaction because it forms an olefin as the final product. Moreover, this reaction was named after the scientist Georg Wittig. The major reagent in this reaction is phosphonium ylide – we can name it as Wittig reagent because this reactant is specific for the Wittig reaction. Apart from the alkene, this reaction gives another product, triphenylphosphine oxide.
Figure 01: Wittig Reaction in a General Equation
Wittig reaction is useful in the production of alkenes in organic synthesis processes. We can classify this reaction as a coupling reaction because it includes the coupling of aldehydes and ketones to triphenylphosphonium ylides. The nature of the produced alkene depends on the stability of the ylide. i.e. unstabilized ylides give Z-alkenes, and stabilized ylides give E-alkene. However, the formation of E-alkene is highly selective in this reaction.
What is Wittig Rearrangement?
Wittig rearrangement is a type of transformation of one form into another form depending on the stability. There are two main types of Wittig rearrangement: 1,2-Wittig rearrangement and 2,3-Wittig rearrangement.
1,2-Wittig rearrangement is a reaction in organic chemistry where an ether undergoes rearrangement with an alkylithium compound. The general chemical formula for this reaction is as follows:
Figure 02: General Chemical Formula for 1,2-Wittig rearrangement
This reaction includes the formation of an alkoxy lithium salt as the intermediate and the final product of the reaction is an alcohol. However, if the ether contains good leavening groups such as cyanide group, (as shown in the above image) which is able to withdraw electrons. This group is eliminated during the rearrangement, forming the corresponding ketone.
During 2,3-Wittig rearrangement, a transformation occurs, converting an allylic ether into a homoallylic alcohol. This transformation occurs via a concerted and a pericyclic process. Therefore, this reaction exhibits a high degree of stereocontrol thus, we can use it in early synthetic routes in stereochemistry. Generally, this Wittig rearrangement reaction requires a strongly basic environment. Moreover, it is a competitive process for the 1,2-Wittig rearrangement.
What is the Difference Between Wittig Reaction and Wittig Rearrangement?
Wittig reaction and Wittig rearrangement are important in organic chemistry. The key difference between Wittig reaction and Wittig rearrangement is that Wittig reaction forms an alkene as the final product while Wittig rearrangement forms an alcohol or the corresponding ketone as the final product.
Below infographic tabulates the differences between Wittig reaction and Wittig rearrangement.
Summary – Wittig Reaction vs Wittig Rearrangement
Wittig reaction and Wittig rearrangement are important in organic chemistry. The key difference between Wittig reaction and Wittig rearrangement is that Wittig reaction forms an alkene as the final product while Wittig rearrangement forms an alcohol or the corresponding ketone as the final product.
Reference:
1. “The Wittig Reaction.” Chemistry LibreTexts, Libretexts, 14 July 2020, Available here.
2. “Wittig Reaction.” Wikipedia, Wikimedia Foundation, 12 July 2020, Available here.
Image Courtesy:
1. “Wittig Reaktion” By Roland Mattern – Roland1952 (Public Domain) via Commons Wikimedia
2. “WittigModification” By V8rik – en:Image:WittigModification.png (CC BY-SA 3.0) via Commons Wikimedia