Acceleration of cope rearrangement by a remote carbenium ion center: theoretical elucidation of the electronic origin

Abstract

The electronic origin of the remarkable acid catalysis of Cope rearrangement found recently in a rigid tetracyclic framework, I, has been probed by means of MNDO calcns. on model systems II and III. The Cope rearrangement paths are calcd. to be fundamentally different for the neutral and the cationic systems. A step-wise process involving two intermediates is the min. energy reaction pathway (MERP) for the Cope rearrangement of the cation III. The calcns. also reveal another intriguing possibility involving a remarkable pyramidal carbocation intermediate IV which is essentially a diolefin π-complex of CH⁺. Both these paths require substantially less activation enthalpies than that computed for the rearrangement of the neutral mol. II.