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Pericyclic Reactions: Introduction01:17

Pericyclic Reactions: Introduction

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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.
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Acyclic diene metathesis polymerization or ADMET polymerization involves cross-metathesis of terminal dienes, such as 1,8-nonadiene, to give linear unsaturated polymer and ethylene. As ADMET is a reversible process, the formed ethylene gas must be removed from the reaction mixture to complete the polymerization process.
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Benzaldehyde, like formaldehyde, lacks an α hydrogen and cannot enolize to form an enolate. Hence, the reaction of benzaldehyde with a ketone in the presence of an aqueous base forms a single crossed product. This reaction is referred to as Claisen–Schmidt condensation.
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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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Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the...
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Regioselective Formation of Enolates01:33

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As depicted in the figure below, the unsymmetrical ketones can form two possible enolates:  less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are  more stable. But the energy required to form kinetic enolates is less.
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Stable Cyclic Peterson Olefination Intermediates.

Julia Landwehrmann1, Beate Neumann1, Hans-Georg Stammler1

  • 1Fakultät für Chemie, Centrum für Molekulare Materialien, Universität Bielefeld, Bielefeld, Germany.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 23, 2026
PubMed
Summary
This summary is machine-generated.

Researchers synthesized stable cyclic intermediates for the Peterson olefination, a silicon-based carbonyl olefination reaction. This study provides crucial evidence for cyclic intermediates in this important organic chemistry transformation.

Keywords:
carbanionsfluorineolefinationreactive intermediatessilicates

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Area of Science:

  • Organic Chemistry
  • Organosilicon Chemistry

Background:

  • The Wittig olefination is a well-understood method for carbonyl olefination.
  • The mechanism of the related Peterson olefination, a silicon analogue, remains less understood.
  • Evidence for cyclic intermediates in Peterson olefination has been scarce.

Purpose of the Study:

  • To synthesize and characterize stable cyclic intermediates of the Peterson olefination.
  • To provide experimental evidence supporting the existence of cyclic intermediates in this reaction.

Main Methods:

  • Reaction of α-silyl carbanions with various ketones.
  • Synthesis of α-silyl carbanions stabilized by three pentafluoroethyl groups and a phenyl group.

Main Results:

  • Successful synthesis and characterization of several stable cyclic Peterson olefination intermediates.
  • Demonstration of the feasibility of forming cyclic intermediates under specific conditions.

Conclusions:

  • The study presents the first stable cyclic Peterson olefination intermediates.
  • This work offers significant insights into the mechanism of the Peterson olefination reaction.