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

The reactivities and torquoselectivities of electrocyclic ring opening reactions of fluoromethyl-substituted cyclobutenes and oxetenes were studied with M06-2X density functional theory. The torquoselectivities of a series of mono-, di-, and trifluoromethylcyclobutenes 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 ςCO bond and the ςCF* orbital (ςCO ςCF*) 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 ςCO bond and trifluoromethyl substituent orbitals compete with the ςCO ςCF* interaction. [ABSTRACT FROM AUTHOR]