1. 17.5 The Wittig and Related Reactions (formation of alkenes)
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17.5 The Wittig and Related Reactions
The Wittig Reaction
(formation of alkenes)
General Reaction:
R´ and R” can be H or alkyl group.
Phosphine oxide
Wittig reagent (a phosphonium ylide)

2. Formation of Wittig Reagents
General Reaction:
base
A phosphonium salt
Ph: phenyl
The alkyl halides need to have at least one H.
Example:
Potassium tert-butoxide

3. Mechanism of Wittig Reaction
oxaphosphetane
betaine

4. Examples of Wittig Reaction
major
minor
Wittig reagents favor the Z (cis) isomer.

5. Reactions of Aldehydes and Ketones with Horner-Emmons Reagent
Horner-Emmons reaction (general reaction):
R = Et (most common)
Phosphate diester
Horner-Emmons reagent

6. Formation of Horner-Emmons Reagent
Arbuzov (Perkow) reaction:
base
R = alkyl, acyl or R’OC(O)-
Stabilized carboanion

7. Mechanism of Horner-Emmons Reaction
oxaphosphetane
betaine
Water insoluble
Water soluble

8. Examples of Horner-Emmons Reaction
> 99%
Horner-Emmons reagents favor the E (trans) isomer.

9. Learning Check
1. What could be the reagent for the following transformation?
2. What should be the product from the following reaction?

10. Learning Check
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3. What could be the product for the following reaction?