Vinylidene from cyclic alkynes

The Fritsch-Buttenberg-Wiechell rearrangement provides a method to expand a cyclic ketone to a cyclic acetylene with an additional carbon atom in the ring [34]. The ketone is first converted to a vinyl bromide or a vinylidene dibromide, from which the corresponding vinylidene carbene is produced with butyllithium. The vinylidene carbene then rearranges to a cyclic alkyne (Scheme 8-10). 

---