Influence of the counteranion on the phenylselenoetherification reaction of nerolidol

Abstract

The pyridine-mediated reactions of nerolidol with both PhSe+ and PhSeCl were investigated using two DFT methods. Comparison of the obtained results provides a description of the counterion influence for the first time. As a consequence of very low solvation free energy of the neutral reactants, addition of the phenylselenyl group to the double bond of nerolidol is an endergonic process, and occurs via a transition state to yield an intermediate that undergoes cyclisation. Due to the influence of the counteranion on the positively charged moiety of the reaction system, the activation free energies in the reaction with PhSeCl are significantly larger than those in the reaction with PhSe+. Thus, only the anti pathway is favoured. The lower activation energy required for the formation of less stable cis-5-ethenyl-5-methyl-2-[6-methyl-2-(phenylseleno)hept-5-en-2-yl]tetrahydrofuran confirms that the examined reaction is kinetically controlled.