MECHANISM OF LITHIUM PERCHLORATE DIETHYL ETHER-CATALYZED REARRANGEMENT OF ALPHA-ENDO-DICYCLOPENTADIENYL AND BETA-ENDO-DICYCLOPENTADIENYL AND ALPHA-EXO-DICYCLOPENTADIENYL AND BETA-EXO-DICYCLOPENTADIENYLVINYL ETHERS - USE OF DEUTERIUM LABELING AND A CHIRAL PROBE

Lithium perchlorate/diethyl ether (LPDE) mediated rearrangement of alp ha- and beta-endo-dicyclopentadienyl vinyl ethers 5 and 6 resulted in the formation df the aldehyde 8, indicating that the mechanism is nonc oncerted and the recombination of the ion pair occurs at the dissociat ed stage and not the intimate ion-pair stage. Proof of this came from deuterium-labeling studies and the use of an optically pure starting m aterial. Furthermore, that the ionic intermediate formed must be symme trical resulting in enantiomeric aldehydes from both normal and allyli c attack corresponding to products of formal 1,3 and 3,3 shifts was se en in the chiral analysis of the benzoate derivative of the aldehydes formed from the optically pure vinyl ether.