endo-Adducts of cyclopenta-or cyclohexa-1, 3-dienes with cyclohexa-1,4-dienes, especially p-benzoquinones (Ia) , cyclise on ultraviolet irradiation to cage-like isomers (Ib) by formation of a cyclobutane ring from the two double bonds. The effects of interaction between the two carbonyl groups in the photoisomers (Ib) appear in their infrared and ultraviolet spectra. * After the appearance of our preliminary note 3 we learnt €hat the photoisomerisation of benzoquinone adducts had been independently observed in the laboratory of Professor C. H. De Puy (Iowa State College, Ames, U.S.A.), who very generously offered to leave the field to us.

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Gupte has developed a much more convenient synthesis: ethyl N-aminocarbamate, made by warming diethy1 carbonate and hYdrazine* is added to phenyl isocyanate, and the product treated with alkali.

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