Caryolene-forming carbocation rearrangements

Abstract

Density functional theory calculations on mechanisms of the formation of caryolene, a putative biosynthetic precursor to caryol- 1(11)-en-10-ol, reveal two mechanisms for caryolene formation: one involves a base-catalyzed deprotonation/reprotonation sequence and tertiary carbocation minimum, whereas the other (with a higher energy barrier) involves intramolecular proton transfer and the generation of a secondary carbocation minimum and a hydrogen-bridged minimum. Both mechanisms are predicted to involve concerted suprafacial/ suprafacial [2 + 2] cycloadditions, whose asynchronicity allows them to avoid the constraints of orbital symmetry. © 2013 Nguyen and Tantillo; licensee Beilstein-Institut.