946. Cyclisations and rearrangements in the isodrin–aldrin series

Abstract

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...

On the mechanism of skeletal rearrangements in the acid catalysed acetylation of isodrin †

“…Some aspects of the results reported here are new. Firstly, our results show that the calculations are in good agreement with the experimental data with a revised mechanism suggesting, in contrast to the literature, 22 that the protonation of isodrin occurs by two pathways characterized by transition states 6 and 5. The second path represents a new kind of protonation in a double-bond system like isodrin, with the intermediate 7 being responsible for the formation of the pentacyclic system.…”

“…In general, these structures are obtained by complex rearrangements which occur when isodrin is treated with acid. 22 In particular, the reaction of isodrin with acetic acid containing sulfuric acid represents a good example for observation of these rearrangements that produce a mixture of four products (Scheme 1): tetracyclic 1, half-cage 2, half-cage 3 and birdcage 4. However, in spite of the various efforts of mechanistic investigations of the solvolysis of the methanesulfonate derivatives, 22-25 most details on the pathway that determines how half-cages 2 and 3 are formed by rearrangement of isodrin are still to be clarified.…”

Synthesis of dieldrin metabolites. 3. Two-step conversion of syn-12-hydroxydieldrin into Klein's metabolite (3,5,6,6,7-pentachloro-11,12-exo-epoxypentacyclo[6.4.0.02,10.03,7.05,9]dodecan-4-one)

“…Moreover, the rate of its (ready) solvolysis was approximately the same as that of the tosylate of anti-7hydroxynorbornene (V), a compound that constitutes one of the classical examples exhibiting anchimeric assistance (its solvolysis rate is 1011 larger than that of its saturated analogue VI. Secondly, although the two electron-withdrawing chlorine atoms attached at the termini of the double bond of syn-12-hydroxydieldrin (Ila) would be expected to much reduce its reactivity toward electrophiles, the formation of the bridged reaction product, IX, as an acetolysis product of the isodrin-derived mesylate (VII) must necessarily have involved initial formation of the bridged carbonium ion, VIII, from which IX is derivable by an unexceptionable transannular hydride shift (Bird et al, 1961) (Figure 3). There remained one feature of the tosylate of syn-12-hydroxydieIdrin (lib) that could affect the outcome of its solvolysis: the epoxy grouping.…”

Woodward-Hoffmann rules: Cycloaddition reactions

“…The short lifetime of alkene excited states does not always allow an encounter of an excited molecule with an unexcited one and places a severe limitation on the photochemical dimerization of alkenes. Immobilization of the reactants in the crystalline state helps overcome this obstacle, and several photochemical dimerizations have been reported under these conditions (28) (eqns. ( 10) and ( 11)).…”