Fritsch–Buttenberg–Wiechell rearrangement

This rearrangement is also possible with alkyl substituents.

Reaction mechanism

The strong base deprotonates the vinylic hydrogen, which after alpha elimination forms a vinyl carbene. A 1,2-aryl migration forms the 1,2-diaryl-alkyne product. The mechanism of the FBW rearrangement was a subject of on-surface studies where the vinyl radical was visualised with sub-atomic resolution.