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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
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Photocyclodehydrofluorination.

Zhe Li1, Robert J Twieg2

  • 1Department of Chemistry and Biochemistry, Kent State University Kent, OH, 44242 (USA).

Chemistry (Weinheim an Der Bergstrasse, Germany)
|September 12, 2015
PubMed
Summary
This summary is machine-generated.

Fluorinated stilbenes undergo photocyclization, eliminating hydrogen fluoride (HF) to form novel fluorinated polycyclic aromatic hydrocarbons. This photocyclodehydrofluorination (PCDHF) offers a new route to valuable materials.

Keywords:
Mallory-type photocyclizationSynthesis designphotocyclodehydrofluorinationphotoreactionsynthetic methods

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Area of Science:

  • Organic Chemistry
  • Photochemistry
  • Materials Science

Background:

  • Mallory photocyclization typically requires oxidants to form phenanthrene products from stilbenes and related compounds.
  • Selective fluorination of polycyclic aromatic hydrocarbons is crucial for advanced materials applications.

Purpose of the Study:

  • To develop a novel method for synthesizing selectively fluorinated polycyclic aromatic hydrocarbons.
  • To explore the photocyclodehydrofluorination (PCDHF) of fluorinated stilbenes and o-terphenyls.

Main Methods:

  • Photoreaction of appropriately fluorinated stilbenes and o-terphenyls.
  • Intramolecular cyclization via dihydrophenanthrene intermediates.
  • Elimination of hydrogen fluoride (HF) during photocyclization.

Main Results:

  • Successful synthesis of selectively fluorinated polynuclear aromatic hydrocarbons.
  • Demonstration of the PCDHF reaction as an oxidant-free pathway.
  • Formation of products with phenanthrene or related heterocyclic substructures.

Conclusions:

  • The PCDHF reaction provides a versatile and efficient route to valuable fluorinated polycyclic aromatic hydrocarbons.
  • This method avoids the need for external oxidants, simplifying the synthetic process.
  • The resulting fluorinated compounds hold significant potential for materials science.