Chapter 17: Aldehydes and Ketones. Nucleophilic Addition to C=O 
Ch 17 contents

The Wittig Reaction
 

alkene synthesis using the Wittig reaction
        ylid           aldehyde or ketone                  alkene 

Reaction type:  Nucleophilic Addition then Elimination

Summary

preparation of a phosphorous ylid
An SN2 reaction between triphenyl phosphine and an alkyl halide followed by treatment with a strong base such as an organolithium reagent. 

Related Reactions

THE WITTIG REACTION
Step 1:
The nucleophilic C of the ylid Wittig reagent adds to the electrophilic C in the polar carbonyl group, electrons from the C=O p bond are used to form a s bond to the +ve P atom. This creates a cyclic intermediate called an oxaphosphetane.
addition of Grignard reagent to an aldehyde
Step 2:
Decomposition of the intermediate by breaking the C-P and C-O s bonds leads to the formation of the C=C p bond of the alkene and triphenyl phosphine oxide.


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