Wittig reaction – Ylid reaction with ketone

Ring formation and decomposition

Click the structures and reaction arrows in sequence to view the 3D models and animations respectively

The carbanion part of the phosphonium ylid acts as the nucleophile, and attacks the cabonyl group of the cyclohexanone. This generates a negatively charged oxygen that can then attack the positively charged phosphorus, giving a four-membered ring called an oxaphosphetane.

This ring structure is unstable and can collapse in a way that forms two double bonds. The mechanism is concerted and gives the alkene which is the product, together with a phosphine oxide which provides the thermodynamic driving force.

Back to Wittig summary

P. A. Byrne and D. G. Gilheany, Chem. Soc. Rev., 2013, 42, 6670.


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