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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.8K
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.
Selection Rules: Photochemical Activation
1.8K
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

2.5K
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
2.5K
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

9.9K
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
9.9K
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry01:28

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

3.7K
The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
3.7K
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

3.5K
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
3.5K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.0K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.0K

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Updated: May 3, 2026

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes
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Programmable Solid-State [2 + 2] Photocycloadditions of Dienes Directed by Structural Control and Wavelength

Liulei Ma1, Gary C George1, Steven P Kelley1

  • 1Department of Chemistry, University of Missouri, 601 S College Avenue, Columbia, Missouri 65211, United States.

Journal of the American Chemical Society
|May 19, 2025
PubMed
Summary
This summary is machine-generated.

Two solid forms of a diene derivative exhibit distinct reactivity and photoresponsivity due to varied π-π stacking. This enables controlled photocycloaddition reactions, yielding diverse products and photoactuating materials.

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Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals
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Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

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Area of Science:

  • Solid-state chemistry
  • Photochemistry
  • Materials science

Background:

  • Molecular and solid-state structures significantly influence material properties.
  • Diene derivatives offer tunable reactivity for chemical transformations.
  • π-π stacking arrangements dictate intermolecular interactions and reactivity in the solid state.

Purpose of the Study:

  • To synthesize and characterize distinct solid-state forms of a diene derivative.
  • To investigate the influence of solid-state structure on photocycloaddition reactions.
  • To explore wavelength-dependent photoreactivity and photomechanical behavior.

Main Methods:

  • Synthesis and crystallization of 1,3-bis((E)-2-bromostyryl)benzene (2Brm).
  • Solid-state characterization including X-ray diffraction to determine π-π stacking.
  • UV-Vis irradiation experiments to induce [2 + 2] photocycloaddition reactions.
  • Analysis of reaction products using spectroscopy and chromatography.
  • Investigation of photomechanical responses under different light wavelengths.

Main Results:

  • Two unique solid-state forms of 2Brm were obtained, differing in π-π stacking geometry.
  • Regiocontrolled [2 + 2] photocycloaddition reactions occurred, yielding distinct regioisomeric products based on crystal packing.
  • Wavelength-dependent photoreactivity allowed programming of discrete cyclobutane-containing products and oligomers/polymers from a single precursor.
  • Wavelength-dependent photomechanical behaviors (photosalience) were observed in the two solid forms.

Conclusions:

  • Solid-state structure is a critical determinant of reactivity and photoresponse.
  • Template-free self-assembly provides a strategy for regiocontrolled solid-state photocycloadditions.
  • This approach allows access to a diverse range of chemical products and offers potential for designing photoactuating materials.