A tangled web—interconnecting pathways to amorphadiene and the amorphene sesquiterpenes

Abstract

Quantum chemical studies on the formation of amorphadiene and the amorphene sesquiterpenes are described. These natural products are commonly thought to arise from distinct pathways involving initial 1,6- and 1,10-cyclization of farnesyl diphosphate, respectively. We have found, using density functional calculations, that the pathway usually invoked for amorphadiene formation is not only energetically feasible, but is also the energetically favored pathway to the amorphenes as a result of a low energy (two-step) 1,5-hydride transfer involving an unusual carbocation containing a 3-center 2-electron [C⋯H⋯C]⁺ bonding array.