Ab Initio Study of Intramolecular Ring Cyclization of Protonated and BF(3)-Coordinated trans- and cis-4,5-Epoxyhexan-1-ol.
The potential energy surface for the rearrangement of cis- and trans-4,5-epoxyhexan-1-ol with acid and the Lewis acid BF(3) to five- and six-membered cyclic ethers has been investigated by ab initio methods. The transition structures involving both inversion and retention of configuration at the reaction center at the HF/6-31G and B3LYP/6-31G levels are characterized. The preference for furan formation over pyran is attributed to the more favorable O-C(ep)-O bond angles at the transition structures for furan formation. The torsional O-C(ep)-C(ep)-O angles associated with tetrahydrofuran and tetrahydropyran formation vary with structure and do not directly correlate with the preferred pathway.
Coxon
James M.
JM
Department of Chemistry, University of Canterbury, Christchurch, New Zealand.
Thorpe
Aaron J.
AJ