Acid-Catalyzed Conversion Of Caryolan-1-ol To Isoclovene: A Computational Investigation Of The Multi-Step Carbocation Rearrangement

Document Type

Article

Publication Date

7-12-2018

Published In

Tetrahedron

Abstract

Acid-catalyzed conversion of caryolan-1-ol to isoclovene involves a multi-step carbocation rearrangement. Electronic structure calculations show that the pathway proceeds through an initial 3° carbocation, as well as a series of three other 3° carbocations. The key stage in which the ring structure is rearranged occurs not as might initially be imagined, in two separate steps with the intermediacy of a 2° carbocation, but rather in a single, concerted but highly asynchronous dyotropic rearrangement. The transition structure for this dyotropic rearrangement strongly resembles the 2° carbocation that would be involved in a stepwise mechanism. However, the dyotropic rearrangement is stereochemically unusual. While one of the bond migrations is suprafacial, as expected, the other is effectively antarafacial. This unusual stereochemical outcome is enforced by the geometric constraints of the polycyclic structure.

Keywords

Carbocation, Rearrangement, Dyotropic, Caryolan-1-ol, Isoclovene, Sesquiterpene, Stereochemistry, Terpenoid

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