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Related Concept Videos

Radical Reactivity: Overview01:11

Radical Reactivity: Overview

Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
Radical Formation: Elimination00:51

Radical Formation: Elimination

Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions with respect to...
Radical Formation: Overview01:03

Radical Formation: Overview

A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the latter, also known...
Preparation of Epoxides03:00

Preparation of Epoxides

Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Radical Formation: Addition00:47

Radical Formation: Addition

Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...

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Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy
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Radical 4-exo cyclizations via template catalysis.

Andreas Gansäuer1, Karsten Knebel, Christian Kube

  • 1Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard Domagk Str. 1, 53121 Bonn, Germany. andreas.gansaeuer@uni-bonn.de

Chemistry (Weinheim an Der Bergstrasse, Germany)
|January 24, 2012
PubMed
Summary
This summary is machine-generated.

This study reveals a super-unsaturated titanocene(III) catalyst activates radicals via hydrogen bonding for 4-exo cyclizations. Computational analysis explains product formation through a disfavored substrate pathway.

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Area of Science:

  • Organometallic Chemistry
  • Catalysis
  • Reaction Mechanisms

Background:

  • Investigating catalytic 4-exo cyclizations without gem-dialkyl substitution presents challenges.
  • Understanding the precise mechanism is crucial for catalyst design and reaction optimization.

Purpose of the Study:

  • To elucidate the mechanism of catalytic 4-exo cyclizations.
  • To identify the key factors enabling cyclizations without gem-dialkyl substitution.

Main Methods:

  • Comparative analysis of cyclic voltammetry, Electron Paramagnetic Resonance (EPR) spectroscopy, and computational studies.
  • Integration of these methods with existing synthetic data.

Main Results:

  • A super-unsaturated 13-electron titanocene(III) complex, activated by hydrogen bonding, proved to be the most active catalyst.
  • The catalyst employs a two-point radical binding strategy essential for successful 4-exo cyclization.
  • Computational studies indicated that the observed trans-cyclobutane product arises from a less stable substrate radical, following a Curtin-Hammett-like scenario.

Conclusions:

  • Supramolecular activation via hydrogen bonding is key for the titanocene(III) catalyst's high activity.
  • The reaction proceeds via a non-obvious pathway involving a disfavored substrate radical to achieve the lowest activation energy for product formation.