Mechanism of lithium perchlorate/diethyl ether-catalyzed rearrangement of α- and β-endo- and -exo-dicyclopentadienyl vinyl ethers: use of deuterium labeling and a chiral probe

Abstract

Lithium perchlorate/diethyl ether (LPDE) mediated rearrangement of α-and β-endo-dicyclopentadienyl vinyl ethers 5 and 6 resulted in the formation of the aldehyde 8, indicating that the mechanism is nonconcerted and the recombination of the ion pair occurs at the dissociated stage and not the intimate ion-pair stage. Proof of this came from deuterium-labeling studies and the use of an optically pure starting material. Furthermore, that the ionic intermediate formed must be symmetrical resulting in enantiomeric aldehydes from both normal and allylic attack corresponding to products of formal 1,3 and 3,3 shifts was seen in the chiral analysis of the benzoate derivative of the aldehydes formed from the optically pure vinyl ether.