Mono-, Di-, and Trifluoroalkyl Substituent Effects on the Torquoselectivities of Cyclobutene and Oxetene Electrocyclic Ring Openings

摘要

The reactivities and torquoselectivities of electroc-yclic ring opening reactions of fluoromethyl-substituted cydobutenes and oxetenes were studied with M06-2X density functional theory. The torquoselectivities of a series of mono-, di-, and trifluoromethylcydobutenes and oxetenes result from the interplay of favorable orbital interactions and closed-shell repulsions. When the substituent rotates inward, there can be a favorable interaction between the breaking sigma(CO) bond and the sigma(CF)* orbital (sigma(CO) -> sigma(CF)*) of the fluoromethyl group in fluoromethyloxetenes. The preference for rotation of a fluoromethyl group is decreased in trifluoromethyloxetenes because closed-shell repulsions between the breaking sigma(CO) bond and trifluoromethyl substituent orbitals compete with the sigma(CO) -> sigma(CF)* interaction.