Wittig reaction

1. Wittig Reaction
A property of carbonyl compounds
 Involves the conversion of aldehydes
and ketones to alkenes with the help of
phosphorous ylides

2. Carbonyl
compound
Ylide Alkene

3. Ylide
• A molecule with adjacent opposite
charges
• Prepared from alkyl halides with
triphenylphosphene

4. Mechanism
• Step 1The negative carbon of the ylide
attaches with carbonyl carbon to form
betaine, a molecule with non-adjacent
opposite charges
C==O
+S -S
+ C6H5)3 P----CR2
+ -
C----O
R2C--P(C6H5)3
+
-

5. • Step 2
Betaine undergoes elimination of triphenyl
phosphine oxide to give alkene
C----O
R2C--P(C6H5)3
+
- C-----O
R2C------P(C6H5)3
C==CR2+(C6H5)3P==O

6. Applications
• Preparation of alkenes from aldehydes and
ketones e.g. acetone recat with ylide to form 2,
methyl propene
C==O + C6H5)3 P----CH2
+ -
C==CH2+(C6H5)3P==O
CH3
CH3
CH3
CH3

7. Applications
• Preparation of alkenes from aldehydes and
ketones e.g. acetone recat with ylide to form 2,
methyl propene
C==O + C6H5)3 P----CH2
+ -
C==CH2+(C6H5)3P==O
CH3
CH3
CH3
CH3