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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.
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
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.
Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction01:22

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation02:47

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
[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.

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Related Experiment Video

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Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
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Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Published on: June 21, 2017

Catalytic intermolecular enal-alkyne [3 + 2] reductive cycloadditions.

Ananda Herath1, John Montgomery

  • 1Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109-1055, USA.

Journal of the American Chemical Society
|October 26, 2006
PubMed
Summary

A new nickel-catalyzed cycloaddition reaction combines simple acyclic molecules into five-membered rings. This reductive process uses triethylborane and a protic solvent for efficient synthesis.

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A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species
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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators
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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators
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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

Published on: November 27, 2015

Area of Science:

  • Organic Chemistry
  • Catalysis
  • Synthetic Methodology

Background:

  • Cycloaddition reactions are fundamental in organic synthesis for constructing cyclic molecules.
  • Developing catalytic methods for [3 + 2] cycloadditions, especially those involving simple acyclic precursors, remains an active area of research.
  • Reductive cycloadditions offer unique pathways to access complex structures from readily available starting materials.

Purpose of the Study:

  • To develop a novel catalytic, intermolecular [3 + 2] reductive cycloaddition reaction.
  • To establish a nickel-catalyzed strategy for the synthesis of five-membered rings from enals and alkynes.
  • To investigate the role of triethylborane as a reducing agent and the influence of protic solvents in this transformation.

Main Methods:

  • Employing a nickel catalyst to mediate the cycloaddition reaction between enals and alkynes.
  • Utilizing triethylborane (Et3B) as a stoichiometric reducing agent to achieve a net two-electron reduction.
  • Conducting the reaction in a protic solvent, identified as a key parameter for successful transformation.

Main Results:

  • Successfully developed a catalytic, intermolecular [3 + 2] reductive cycloaddition of enals and alkynes.
  • Demonstrated a nickel-catalyzed strategy for efficiently combining two simple acyclic pi-systems.
  • Obtained five-membered ring products through a net two-electron reduction process.
  • Highlighted the critical role of protic solvents in facilitating the reaction.

Conclusions:

  • The developed method provides an efficient route to five-membered heterocyclic compounds.
  • This nickel-catalyzed reductive cycloaddition offers a valuable tool for organic synthesis.
  • The reaction's reliance on simple starting materials and mild conditions makes it synthetically useful.