On the Thermal Behavior of Butatrienecarboxylic Acid Derivatives: Crystal and Molecular Structure of a [4]Radialene Tetracarboxylic Ester

A thermal solid‐state reaction with exclusive formation of the all ‐Z‐[4]radialene 1 was observed for dimethyl (E)‐1,4‐diphenyl‐1,2,3‐butatriene‐1,4‐dicarboxylate. The four‐membered ring in 1 is very strongly puckered; the substituents form an irregular propeller structure in which the ester and phenyl groups are twisted counter to each other.