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Acid-Catalyzed α-Halogenation of Aldehydes and Ketones01:21

Acid-Catalyzed α-Halogenation of Aldehydes and Ketones

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By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
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Preparation of 1° Amines: Hofmann and Curtius Rearrangement Overview01:07

Preparation of 1° Amines: Hofmann and Curtius Rearrangement Overview

3.3K
In the presence of an aqueous base and a halogen, primary amides can lose the carbonyl (as carbon dioxide) and undergo rearrangement to form primary amines. This reaction, called the Hofmann rearrangement, can produce primary amines (aryl and alkyl) in high yields without contamination by secondary and tertiary amines.
3.3K
Keto–Enol Tautomerism: Mechanism01:14

Keto–Enol Tautomerism: Mechanism

6.1K
The keto and enol forms are known as tautomers and they constantly interconvert (or tautomerize) between the two forms under acid or base catalyzed conditions. Both the reactions involve the same steps—protonation and deprotonation— although in the reverse order.
6.1K
α-Alkylation of Ketones via Enolate Ions01:10

α-Alkylation of Ketones via Enolate Ions

3.3K
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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[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

2.9K
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
2.9K
Aldol Condensation with β-Diesters: Knoevenagel Condensation01:27

Aldol Condensation with β-Diesters: Knoevenagel Condensation

3.2K
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as β-diesters to produce substituted olefins.
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α-Ketol Rearrangement for Accessing Tetracyclic Natural Products.

Alexandru Sara1, Ulrike Eggert1, Markus Kalesse1,2

  • 1Institute of Organic Chemistry, Gottfried Wilhelm Leibniz Universität Hannover, 30167 Hannover, Germany.

Organic Letters
|July 22, 2025
PubMed
Summary
This summary is machine-generated.

This study introduces a new method for synthesizing tetracyclic natural products, crucial for diverse biological activities. The protocol enables stereoselective synthesis and inversion of key molecular structures.

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Area of Science:

  • Organic Chemistry
  • Natural Product Synthesis
  • Medicinal Chemistry

Background:

  • Tetracyclic natural products, based on the tetracycline skeleton, exhibit a wide range of biological activities.
  • A key structural element in these compounds is a tertiary alcohol within a cis-decalin framework.

Purpose of the Study:

  • To develop a comprehensive protocol for synthesizing tricyclic building blocks and complete carbon frameworks.
  • To enable stereoselective synthesis of specific enantiomers and their inversion.

Main Methods:

  • Development of a novel synthetic methodology.
  • Stereoselective synthesis of target molecules.
  • Ketol rearrangement for enantiomeric inversion.

Main Results:

  • Successful synthesis of tricyclic building blocks and complete carbon frameworks.
  • Demonstrated stereoselective synthesis of a desired enantiomer.
  • Achieved inversion to the opposite enantiomer using ketol rearrangement.

Conclusions:

  • The presented protocol offers a versatile approach to tetracyclic natural product synthesis.
  • This methodology is valuable for accessing enantiomerically pure compounds and their isomers.