Molecular orbital studies of the intramolecular reaction of protonated cis- and trans-3,4-epoxypentan-1-ol

The transition structures for the intramolecular reaction of protonated cis- and trans-3,4-epoxypentan-1-ol (13) and (16), which result in the formation of protonated cis- and trans-2-methylfuran-3-ols (14) and (18) with inversion and retention, have been determined at the ab initio MP2/6-31G* and hybrid density functional B3LYP/6-31G* levels of theory. Intrinsic reaction coordinate calculations for the lower energy inversion pathways for formation of the 8-methylfuran-3-ols show that intramolecular attack occurs in concert with ring opening. The reaction pathways are far from optimum for best orbital overlap, reflecting the strained bicyclic nature of the transition structures.