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

Abstract

1,8,9,10,11,11-Hexachlorotetracyclo[6.2.1.1^3,6.0^2,7]dodec-9-en-4-exo-yl acetate, tetracyclic1; 1,2,2,3,10,11-hexachloropentacyclo[5.4.1.0^3,10.0^4,12.0^5,9]dodecan-8-exo-yl acetate, half-cage2; 1,2,2,3,10,11-hexachloropentacyclo[5.4.1.0^3,10.0^4,12.0^5,9]dodecan-8-endo-yl acetate, half-cage3 and 1,9,10,11,11,12-hexachlorohexacyclo[5.4.1.0^2,6.0^3,10.0^4,8.0^9,12]dodecane, birdcage4 were obtained from acid catalysed acetylation of isodrin. It was observed that the intramolecular rearrangement control is highly dependent on reaction time. The equilibria involved in these rearrangements were determined by gas chromatography. Semiempirical calculations at the PM3-MNDO, AM1 and MNDO levels have been performed to obtain the optimized geometry of the reagent, products, intermediates and transition states for the rearrangement mechanism. The results of the calculations are in good agreement with the experimental data. On the basis of the theoretical and experimental investigations we propose a revised mechanism which involves a new transition state and a new non-classical reaction intermediate.