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Related Concept Videos

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.
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.
[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.
Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation01:27

Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation

Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, β-ketoesters, or β-diketones) and α,β-unsaturated carbonyl acceptors. Named after Sir Robert Robinson, who discovered it, this reaction yields a six-membered ring with three new C–C bonds (two σ bonds and one π bond).
Pericyclic Reactions: Introduction01:17

Pericyclic Reactions: Introduction

Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
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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Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
07:49

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Published on: February 20, 2020

Iron-catalyzed intermolecular [2π+2π] cycloaddition.

Sarah K Russell1, Emil Lobkovsky, Paul J Chirik

  • 1Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.

Journal of the American Chemical Society
|May 24, 2011
PubMed
Summary
This summary is machine-generated.

Bis(imino)pyridine iron complexes catalyze the [2π + 2π] cycloaddition of ethylene and butadiene. An iron metallocycle intermediate was isolated, revealing insights into the catalytic mechanism and cyclometalation pathways.

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Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of &#945;-Imino &#947;-Lactones and Alkylidene Pyrazolones
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Published on: February 7, 2019

Area of Science:

  • Organometallic Chemistry
  • Catalysis
  • Organic Synthesis

Background:

  • Bis(imino)pyridine ligands are versatile scaffolds in coordination chemistry.
  • Iron complexes are increasingly studied as sustainable alternatives to precious metal catalysts.
  • Nitrogen fixation and C-C bond formation are key challenges in catalysis.

Purpose of the Study:

  • To investigate the catalytic activity of bis(imino)pyridine iron dinitrogen compounds in cycloaddition reactions.
  • To elucidate the mechanism of the intermolecular [2π + 2π] cycloaddition of ethylene and butadiene.
  • To identify and characterize key intermediates in the catalytic cycle.

Main Methods:

  • Synthesis and characterization of bis(imino)pyridine iron dinitrogen complexes.
  • Catalytic testing for the cycloaddition of ethylene and butadiene.
  • Stoichiometric reactions to isolate and study reaction intermediates.
  • Deuterium labeling studies to probe reaction pathways.

Main Results:

  • The iron complexes ((iPr)PDI)Fe(N2)2 and [((Me)PDI)Fe(N2)]2(μ2-N2) efficiently catalyze the [2π + 2π] cycloaddition.
  • An iron metallocycle intermediate was isolated and shown to be catalytically active.
  • Diene-induced C-C reductive elimination from the metallocycle was observed.
  • Deuterium labeling revealed competitive cyclometalation of the ligand aryl substituents.

Conclusions:

  • Bis(imino)pyridine iron complexes are effective catalysts for vinylcyclobutane synthesis.
  • The catalytic cycle involves an iron metallocycle intermediate undergoing reductive elimination.
  • Ligand cyclometalation is a competing pathway during catalysis.