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The pyrolysis of diphenylcyclopropenone monohydrate (II) at 150°C afforded α-phenyl-trans-cinnamic anhydride (VI). It was proved that the reaction consists of two main steps, the nucleophilic attack of water on I to yield α-phenyl-trans-cinnamic acid (IV), and the reaction of I with IV, thus finally yielding VI. The same type of reaction as that of I with IV was also observed when I was heated in phenol to afford phenyl α-phenyl-trans-cinnamate (XII). The reaction of I with the weak nucleophilic reagent, α-phenyl-trans-cinnamamide (XIV), afforded a monoimino derivative of VI (XVI), which is believed to be produced by the nucleophilic attack of the amide-oxygen of XIV on the carbonyl-carbon of I.

Scheme 1

The title compounds were prepared, and their physical and chemical properties were investigated. The reduction of the cyclobutenes with lithium aluminum hydride afforded halogenfree cyclobutane. The mechanism of the reduction is discussed. The cyclobutenes showed their K-bands in a wavelength region ca. 100 nm shorter than in the cases of the corresponding cyclobutanes. Furthermore, the K-band of the cyclobutenes is comparable to that of 1-phenylbuta-1,3-diene. On the basis of the electronic spectral data, a puckered structure was postulated for the cyclobutenes.