Wittig reaction ----(Organic)

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
+C
6H
5)
3 P----CR2
+-
C----O
R
2C--P(C
6H
5)
3
+
-

5. •Step 2
Betaine undergoes elimination of triphenyl
phosphine oxide to give alkene
C----O
R
2C--P(C
6H
5)
3
+
- C-----O
R
2C------P(C
6H
5)
3
C==CR
2+(C
6H
5)
3P==O

6. Applications
•Preparation of alkenes from aldehydes and
ketones e.g. acetone recat with ylide to form 2,
methyl propene
C==O+C
6H
5)
3 P----CH2
+-
C==CH
2+(C
6H
5)
3P==O
CH
3
CH
3
CH
3
CH
3

7. Applications
•Preparation of alkenes from aldehydes and
ketones e.g. acetone recat with ylide to form 2,
methyl propene
C==O+C
6H
5)
3 P----CH2
+-
C==CH
2+(C
6H
5)
3P==O
CH
3
CH
3
CH
3
CH
3