We characterize the stabilizing features of a macrocyclic sesquiterpene cation using borane, ammonium and methylene substitution using quantum chemical calculations. The context for our study is the elucidation of sesquiterpene biosynthesis mechanisms, which are being clarified with the assistance of computational methods. This study centers upon the humulyl cation, a key intermediate in several sesquiterpene biosynthetic pathways, and has three major focuses: characterization of ground-state structures (zero imaginary frequencies), characterization of transition-state structures (first-order saddle points with one imaginary frequency), and definition of the potential energy surfaces connecting these stationary points with intrinsic reaction coordinates. Taken together, this approach allowed us to identify stabilizing features of the carbenium ion and to address the effect of the carbenium ion on the structure of the humulyl macrocycle. Computational techniques provide useful models for compounds that may be difficult to synthesize in the laboratory, so we were able to distinguish electrostatic and electronic effects by substituting the carbocation with borane (preserving pi-accepting capabilities), ammonium (preserving charge), and methylene (preserving neither charge nor pi-accepting capabilities). In our studies we have observed four major modes of stabilization: hyperconjugation, transannular C<sup>+</sup>•••π(alkene), transannular C<sup>+</sup>•••H–C interactions, and carbon-carbon bond formation.

Using borane, ammonium, and methylene substitution to characterize stabilizing features of a macrocyclic sesquiterpene cation

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.