Olefination

Conversion of a carbonyl or related precursor into an alkene. Atom mapping and E/Z selectivity depend on the chosen reagent class.

Reaction of a phosphorus ylide with a carbonyl compound to form an alkene. The carbonyl carbon and ylidic carbon become the two alkene atoms; the oxygen is transferred to phosphorus.

A Wittig reaction with $\mathrm{P}{\mathrm{h}}_3\mathrm{P}=\mathrm{C}{\mathrm{H}}_2$ that replaces a carbonyl oxygen by $=\mathrm{C}{\mathrm{H}}_2$. On a cyclic ketone it installs an exocyclic methylene without inserting a new ring atom.

Conditions favouring a Z alkene in a Wittig reaction, often using a nonstabilized ylide under kinetic, salt-controlled conditions. Isolation or verification is still required when complete stereoselectivity is not established.