THE WITTIG REACTION
INTRODUCTION: The Wittig reaction is a method for the synthesis of alkenes from carbonyl compounds. An aldehyde or a ketone can react
with a substance known as a phosophorus ylide to yield a variety of alkenes with different degrees of substitution and specific structural
features. This reaction is a more elegant way for to synthesize alkenes than regular elimination reactions because it is very flexible in terms
of tailoring product structure and affords good yields.
R1
Ph
O
+ Ph
R2
R1
R3
R4
R2
R4
P
Ph
aldehyde
or ketone
R3
alkene
phosphorus
ylide
(Ph=phenyl)
Example
H
H
+
ether
(Ph)3P
10o
O
3-Methyl-3-hexene
One of the greatest advantages of the Wittig reaction is that the position of the double bond in the product is unambiguous, compared to
elimination reactions, where the product is usually a mixture of isomers.
H
Wittig
+
+ (Ph)3P
O
Br
(Ph)3P
O
CH2
H
E2
+
CH2
(mixture)