Vinylcyclopropane oxygenation. Ab initio transition state analysis of 5-hexenylperoxy radical cyclization

Structure and energy calculations at the MP2/6-31G*//UHF/6-31G* level of four transition states for the cyclization of the 3-methyl-, and independently, the 3-fluoro-5-hexenylperoxy radical have been recorded. These calculations indicate that while the methyl substituent prefers to adopt an equatorial disposition on a chair-like transition state construct, the fluorine atom exhibits a strong preference for an axial alignment on the chair-like species. Boat-like transition states are significantly less favored than the chair-like alternatives, in contrast to the results of similar calculations in the all carbon (i.e., 5-hexenyl radical) cyclizations.