Whereas biphenyl‐4,4′‐dicarbonyl dichloride reacts with methylenetriphenylphosphorane to give the expected bis(acylylide) 1, the same reaction of biphenyl‐2,2′‐dicarbonyl dichloride results in a multistep rearrangement leading to the zwitterionic 2‐[1,3‐bis(triphenylphosphonio)prop‐1‐en‐3‐id‐2‐yl]biphenyl‐2′‐carboxylate 2. X‐ray crystal structures of both 1 and 2 are reported.