Formation of stilbenes and spiro-oxetanes in the reactions of phenyldiazomethanes with chloranil

The reactions of several phenyldiazomethanes with chloranil gave stilbenes and spiro-oxetanes at 20°C. Stilbenes were major products and the thermodynamically less stable $\text{cis}$-isomers prevaled about 2 to 3 times more than $\text{trans}$-ones depending on the solvents and the substituents of phenyldiazomethanes. On the other hand, stable $\text{trans}$-isomers were obtained exclusively in the case of the oxetanes. The stereochemistry and the mechanism of these reactions will be discussed.