Quantum chemical dissection of the classic terpinyl/pinyl/bornyl/camphyl cation conundrum—the role of pyrophosphate in manipulating pathways to monoterpenes

Abstract

Based on quantum chemical studies, mechanisms to form bornyl diphosphate from geranyl diphosphate are suggested. While bornyl diphosphate is usually proposed to be generated via combination of the pyrophosphate group with a secondary bornyl cation, quantum chemical computations indicate that the bornyl cation is actually not a minimum. Instead, concerted attack of the pyrophosphate group coupled with an alkyl shift could yield bornyl diphosphate from either the pinyl cation or the camphyl cation. Hints of bifurcating pathways on the energy surfaces for such reactions were also uncovered. Of particular note is the development and validation of a large model of the pyrophosphate counterion treated entirely with quantum chemistry.