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.

Treatment of the stereoisomeric insecticides , isodrin and aldrin, with acid induces a series of cyclisation, rearrangement, and hydride transfer t o form a mixture of saturated and unsaturated products, the most stable of which is the saturated isomer with a cyclobutane ring in place of the two double bonds of isodrin. On reaction with acid and on acetolysis of the methanesulphonates of related alcohols five different ring systems are produced.The results, inter dia, prove the configurations previously assumed for isodrin and aldrin, whose ring systems have now been interconverted. THE isomeric chlorohydrocarbon insecticides, aldrin and isodrin, offer attractive frameworks for the study of transannular interactions, both chemical and spectroscopic: but first their configurations must be considered.by the addition of bicycloheptadiene to hexachlorocyclopentadiene : knowing the tendency for exo-addition of dienes to bicycloheptadiene and allowing for the large size of the gem-dichloro-group, one might expect aldrin to have the configuration (I) rather than any of the other three possibilities. Isodrin is made3 by addition of hexachlorobicycloheptadiene (11) to cyclopentadiene : here the large gem-dichlorogroup in the dienophile (11) is likely to force addition of cyclopentadiene from the endo-side. Of the two structures resulting from endo-addition, (111) avoids the repulsion between the methylene and dichloroethylene groups present in the other.The double bonds in a diene of structure (111) are very close to one another and on irradiation would be expected to join up forming a cyclobutane ring.4 We therefore applied the test of irradiating a solution of isodrin in a silica vessel with a mercury arc. That the product was saturated was shown by the usual chemical tests, and the disappearance of the dichloroethylene chromophore was confirmed by the absence of its characteristic, strong band at about 1600 cm.-l. The low end-absorption of the product at 200 mp, where the dichloroethylene compounds have E about 9000, definitely established that the product was saturated. Since systematic names in this series are so cumbersome * we shall refer to this isomer as the cage-compound (IV). Its formation by treatment that left aldrin unchanged proves the configuration of isodrin (111). The isodrin and aldrin series are interconvertible by rearrangements that affect only the unchlorinated part of the molecule (see below) : aldrin must, therefore, have the configuration (I).Attention was next turned to the action of electrophilic reagents on isodrin (111), as its stereochemistry clearly favours transannular reactions. Indeed the products obtained on treatment of isodrin with sulphuric acid in wet dioxan were entirely saturated. The two main components were the cage-compound (IV) and an alcohol, m. p. 204". We learnt later that Lidov and Bluestone had described in a patent the conversion of isodrin * In a preliminary note (Cookson and Crundwell, Chem. and Ind., 1958, 1004) we wrote that we were tempted t o call this isomer " ph...

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