Dimethylation of cholestenone

α,β-Unsaturated steroidal ketones are the classic example of deconjugative alkylation. With potassium tert-butoxide, cholest-4-en-3-one forms the conjugated dienolate (it loses the C6 hydrogen, in the γ position), which is methylated at C4 (α). The second methylation again takes place at C4 and the double bond ends up in the 5,6 position: 4,4-dimethylcholest-5-en-3-one is obtained.

4,4-Dimethyl steroids, such as lanosterol, are intermediates in the biosynthesis of cholesterol, and these synthetic compounds have been used to study it.