title: Positioning a Carbon-Fluorine Bond over the π Cloud of an Aromatic Ring: A Different Type of Arene Activation.
abstract: It is known that the fluoro group has only a small effect on the rates of electrophilic aromatic substitutions. Imagine instead a carbon-fluorine (C-F) bond positioned tightly over the π cloud of an aryl ring-such an orthogonal, noncovalent arrangement could instead stabilize a positively charged arene intermediate or transition state, giving rise to novel electrophilic aromatic substitution chemistry. Herein, we report the synthesis and study of molecule 1, containing a rigid C-F⋅⋅⋅Ar interaction that plays a prominent role in both its reaction chemistry and spectroscopy. For example, we established that the C-F⋅⋅⋅Ar interaction can bring about a >1500 fold increase in the relative rate of an aromatic nitration reaction, affording functionalization on the activated ring exclusively. Overall, these results establish fluoro as a through-space directing/activating group that complements the traditional role of fluorine as a slightly deactivating aryl substituent in nitrations.
authors.affiliation: Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
authors.forename: Maxwell Gargiulo
authors.initials: MG
authors.lastname: Holl
authors.affiliation: Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Struble
authors.affiliation: Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
authors.forename: Prakhar
authors.initials: P
authors.lastname: Singal
authors.affiliation: Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
authors.forename: Maxime A
authors.initials: MA
authors.lastname: Siegler
authors.affiliation: Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA. lectka@jhu.edu.
authors.forename: Thomas
authors.identifier: 0000-0003-3088-6714
authors.initials: T
authors.lastname: Lectka
keywords: arenes; aromatic substitution; carbocations; fluorine; neighboring-group effect