The ylid then undergoes a multistep reaction with an aldehyde or (in our case) a ketone.
Step 1: Nucleophilic Attack on C=O
Step 2: Formation of the Oxaphosphetane
Step 3: Fragmentation of the Oxaphosphetane--Alkene Release
|
Wittig reactions start with formation of the reagent. This is called an "ylid" (pron. ill-id), and is characterized by positive and negative charges on adjacent atoms. There is some controversy over whether a π bond actually forms, but formally this does provide rationale for the stability of the ylid and the acidity of the phosphonium salt:
The ylid then undergoes a multistep reaction with an aldehyde or (in our case) a ketone. |
|
Step 1: Nucleophilic Attack on C=O |
|
Step 2: Formation of the Oxaphosphetane |
|
Step 3: Fragmentation of the Oxaphosphetane--Alkene Release |
|