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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

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.
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

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

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.
Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene01:14

Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene

Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

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.
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

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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Photochemical Manganese-Catalyzed [2 + 2 + 2] Cycloaddition Reactions.

Benedikt N Baumann1, Phong Dam2, Jabor Rabeah2

  • 1Institute for Catalysis (INCA), Johannes Kepler University Linz (JKU), Altenberger Strasse 69, Linz 4040, Austria.

ACS Catalysis
|April 10, 2025
PubMed
Summary

Manganese(I) complexes catalyze photochemical cyclotrimerization of triynes under mild conditions. This versatile method efficiently synthesizes complex molecules, including phosphinines, with broad functional group tolerance.

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Area of Science:

  • Organometallic Chemistry
  • Photochemistry
  • Organic Synthesis

Background:

  • Cyclotrimerization reactions are fundamental in organic synthesis.
  • Developing efficient catalytic systems for triyne cyclotrimerization remains a challenge.
  • Photochemical methods offer unique reactivity pathways under mild conditions.

Purpose of the Study:

  • To develop a novel manganese(I)-catalyzed photochemical method for triyne cyclotrimerization.
  • To investigate the influence of ligands and counteranions on catalytic efficiency.
  • To explore the scope and limitations of the developed methodology for synthesizing complex organic molecules.

Main Methods:

  • Utilized manganese(I) complexes, specifically MnBr(CO)5 with phosphine ligands like dppm.
  • Employed photochemical irradiation under mild temperatures (30-80 °C) without photoinitiators.
  • Conducted catalytic screening and mechanistic studies (experimental and theoretical).

Main Results:

  • Achieved efficient cyclotrimerization of triynes using Mn(I) catalysts under irradiation.
  • Demonstrated broad substrate scope, tolerating diverse functional groups (e.g., alkyl, aryl, Bpin, SiMe3, PPh2).
  • Successfully synthesized 2-fold cyclization products from oligoalkynes and unique phosphinines from diynes and phosphaalkynes.

Conclusions:

  • The Mn(I)-catalyzed photochemical cyclotrimerization is a robust and versatile synthetic tool.
  • Ligand choice and counteranions are critical for optimizing catalytic performance.
  • Mechanistic insights reveal the importance of ligand dissociation and Mn carbonyl species in the catalytic cycle.