The Chemistry of Phenylcyclobutenediones

Phenylcyclobutenediones are easily obtainable and very stable. Depending on the nature of the substituent R in position 3, they may be formally regarded as vinylogous carboxylic acid derivatives (Rhalogen, OCH3, OH, SH) or as α,β‐unsaturated diketo compounds (RH, alkyl, aryl). Their behavior in reactions justifies this approach. Ring contraction, ring expansion, and ring cleavage reactions are described.