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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

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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.
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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

Cycloaddition Reactions: Overview

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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.
3.7K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.7K
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.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.7K
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

4.1K
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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Flow Update for a Cossy Photocyclization.

Takahide Fukuyama1, Yuki Fujita1, Muhammad Abid Rashid1

  • 1Department of Chemistry, Graduate School of Science, Osaka Prefecture University , Sakai, Osaka 599-8531, Japan.

Organic Letters
|October 14, 2016
PubMed
Summary
This summary is machine-generated.

A novel photocyclization reaction using organohalides and a C-C triple bond was achieved in a flow reactor. This efficient method offers a scalable route for synthesizing valuable chemical products.

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Area of Science:

  • Organic Chemistry
  • Photochemistry
  • Flow Chemistry

Background:

  • Photocyclization reactions are crucial for synthesizing complex organic molecules.
  • Traditional batch methods can be inefficient and difficult to scale.
  • Radical-mediated reactions offer unique synthetic pathways.

Purpose of the Study:

  • To investigate a Cossy 5-exo-dig photocyclization of organohalides onto a C-C triple bond.
  • To explore the mechanism of this photocyclization reaction.
  • To develop a scalable flow synthesis method for the product.

Main Methods:

  • Utilized a flow photomicroreactor for the photocyclization reaction.
  • Employed a deuterium labeling study to elucidate the reaction mechanism.
  • Scaled up the synthesis using a larger volume flow reactor.

Main Results:

  • The photocyclization proceeded rapidly with minute residence times in the flow reactor.
  • A nonchain radical mechanism was supported, with triethylamine cation radical as the hydrogen source.
  • Scalable flow synthesis successfully yielded 4 g of the product in high yield.

Conclusions:

  • Flow chemistry enables efficient and rapid photocyclization reactions.
  • The proposed radical mechanism is supported by experimental evidence.
  • The developed flow synthesis is scalable and high-yielding for practical applications.