 Wittig methylenation

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.