Density Functional Theory Calculations of the Effect of Fluorine Substitution on the Cyclobutylcarbinyl to 4-Pentenyl Radical Rearrangement

Abstract

The effects of fluorine substitution on the cyclobutylcarbinyl to 4-pentenyl radical rearrangement and on the strain of cyclobutane have being studied using density functional theory, the ring-opening being modestly inhibited and the strain generally not greatly affected. Perfluorocyclobutane is predicted to have 6 kcal/mol less strain than cyclobutane. Cyclizations of 1,1,2,2-tetrafluoro- and 1,1,2,2,3,3-hexafluoro-4-pentenyl radicals should be significantly enhanced ( approximately 2400 times faster) relative to the parent system. The calculations are consistent with the few experimental data available.

Extremely facile ring inversion and rearrangement in fluorobicyclo[2.1.0]pentanes

“…Rearrangement of 10 with a strong Lewis acid was (4) expected to yield ketone 11, a well precedented transformation of fluoroepoxides [8], but gave instead octafluorocyclopentene (12) with extrusion of carbon monoxide (Eq. (5)). Apparently the desired process was subverted by strain in the ring system, which caused a C-C bond shift to preclude fluorine migration.…”

“…We initially assumed that this value represents an upper limit for the free energy of cleavage of the central bond of bicyclopentane 8, as is the case for the inversion barrier of the parent bicyclopentane (5). However, theoretical calculations point to a different conclusion.…”

“…Though substitution by fluorine on cyclobutane rings has a modest stabilizing effect [4], fluoro substituents strongly destabilize cyclopropane rings [5]. To learn how weak the central bond of a fluorobicyclopentane can be, we therefore chose as www.elsevier.com/locate/fluor Journal of Fluorine Chemistry 127 (2006) [688][689][690][691][692][693][694][695][696][697][698][699][700][701][702][703] target molecules bicyclopentanes fully fluorinated on the threemembered rings; namely, 6-8.…”

Cyclizations

“…Cyclobutanes can be formed by intramolecular addition of carbanions or radicals to C-C double bonds only if the latter are substituted with electron-withdrawing groups (see, e.g., Schemes 9.20 and 9.21) [81] or otherwise activated toward attack by nucleophiles. Activation by an alkynyl group or a cumulated double bond can be sufficient to promote cyclobutane formation (Scheme 9.20).…”

Reaction Mechanism of the Multi‐channel Decomposition Reactions of 1‐Pentenyl Free Radicals

“…[5][6][7] 1-Pentene is an important decomposition product of normal alkyl, and radical attack on it will produce 1-pentenyl radicals, especially in combustion processes. 8,9 1-Pentenyl is an important functional group, but there are only few literatures 10,11 regarding its reaction mechanism. Tsang 11 predicted some decomposition rate constants of 1-pentenyl radicals, but density functional theory (DFT) studies on its reaction mechanism were never reported.…”