Methylenation of 4-tert-butylcyclohexanone

(Trimethylsilyl)methylmagnesium chloride adds to 4-tert-butylcyclohexanone in ether and, after hydrolysis, gives the β-hydroxysilane. With magnesium as the counterion the alkoxide does not eliminate, and the alcohol can be isolated.

Treatment with potassium hydride in THF forms the potassium alkoxide, which immediately eliminates potassium trimethylsilanolate and gives 1-tert-butyl-4-methylenecyclohexane. As the double bond is exocyclic and 1,1-disubstituted, geometry is not an issue here; the advantage over the Wittig reaction is that the reagent is less basic and does not enolize the ketone.