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Related Concept Videos

Dehydration of Aldols to Enals: Base-Catalyzed Aldol Condensation01:14

Dehydration of Aldols to Enals: Base-Catalyzed Aldol Condensation

6.7K
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy aldehyde formed in a base-catalyzed aldol addition reaction dehydrates on heating to yield an unsaturated carbonyl product, which is commonly referred to as an enal.
6.7K
Base-Catalyzed Aldol Addition Reaction01:08

Base-Catalyzed Aldol Addition Reaction

4.2K
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy carbonyl compound.
4.2K
Acid-Catalyzed Aldol Addition Reaction01:15

Acid-Catalyzed Aldol Addition Reaction

3.1K
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1.
3.1K
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry01:28

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

4.5K
The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
4.5K
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

11.9K
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.
11.9K
Dehydration of Aldols to Enones: Acid-Catalyzed Aldol Condensation00:43

Dehydration of Aldols to Enones: Acid-Catalyzed Aldol Condensation

2.8K
As shown in Figure 1, under acidic conditions, the β-hydroxy ketone undergoes dehydration via an E1 elimination reaction to form an enone.
2.8K

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Updated: Dec 7, 2025

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

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An enzymatic Alder-ene reaction.

Masao Ohashi1, Cooper S Jamieson2, Yujuan Cai3

  • 1Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.

Nature
|October 1, 2020
PubMed
Summary

Researchers discovered new enzymes called pericyclases that catalyze specific chemical reactions. These enzymes control reaction outcomes, offering insights into biological catalysis and enabling the design of novel catalysts.

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Area of Science:

  • Biochemistry
  • Organic Chemistry
  • Enzymology

Background:

  • Designing selective catalysts for complex molecules is a key challenge in chemical research.
  • Nature utilizes enzymes, like pericyclases, to achieve high selectivity in pericyclic reactions, including cycloadditions.
  • Understanding the mechanisms behind enzymatic selectivity, particularly periselectivity, remains difficult.

Purpose of the Study:

  • To discover and characterize novel pericyclases catalyzing previously unknown biological reactions.
  • To elucidate the mechanisms by which these enzymes achieve high stereoselectivity, regioselectivity, and periselectivity.
  • To engineer pericyclases with altered catalytic functions through rational design.

Main Methods:

  • Discovery and characterization of two homologous pericyclase groups.
  • In vitro biochemical assays to determine enzyme activity and selectivity.
  • Computational studies to rationalize observed reactivities and guide enzyme engineering.
  • X-ray crystallography to obtain enzyme co-crystal structures.
  • Site-directed mutagenesis to create and test enzyme variants.

Main Results:

  • Identification of pericyclases catalyzing an Alder-ene reaction (new to biology) and a stereoselective hetero-Diels-Alder reaction.
  • Rationalization of distinct reactivities and selectivities in nearly identical active sites using computational and structural data.
  • Demonstration of engineered pericyclases with reversed periselectivities (Alder-ene to hetero-Diels-Alder and vice versa).

Conclusions:

  • Pericyclases can catalyze diverse pericyclic reactions, including the Alder-ene reaction, expanding the known repertoire of enzymatic catalysis.
  • Enzyme active site architecture dictates high regioselectivity and periselectivity, offering a model for catalyst design.
  • Enzyme engineering can predictably alter catalytic function and selectivity, paving the way for novel biocatalyst development.