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Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization01:13

Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization

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Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic β-ketoester as the final product. Commonly, 1, 6 and 1, 7-diesters are preferred substrates for the reaction since the generated five, and six-membered cyclic β-keto esters are particularly more stable.
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Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry01:29

Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry

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Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.0K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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Diels–Alder Reaction Forming Cyclic Products: Stereochemistry01:28

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

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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.
4.4K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.7K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Updated: Nov 24, 2025

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
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Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

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Una policetida ciclasa que forma lactonas de anillo medio

De-Wei Gao, Cooper S Jamieson, Gaoqian Wang1

  • 1State Key Laboratory of Bio-organic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Shanghai, China.

Journal of the American Chemical Society
|December 22, 2020
PubMed
Resumen

Los investigadores descubrieron una enzima tioesterasa, DcsB, que cataliza eficientemente las lactonizaciones de anillo medio. Esta enzima, de la vía de la decarestrictina C1, muestra un amplio alcance en el sustrato y ofrece potencial como biocatalizador para desafiar la síntesis de la lactona.

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Área de la Ciencia:

  • La bioquímica
  • Química orgánica
  • Enzimología

Sus antecedentes:

  • Las lactonas de anillo medio son difíciles de sintetizar debido a la energía de ciclización desfavorable.
  • La vía de biosíntesis de la decarestrictina C1 implica la formación de productos naturales complejos.

Objetivo del estudio:

  • Identificar y caracterizar las enzimas implicadas en la formación de lactona de anillo medio.
  • Explorar el potencial del DcsB como biocatalizador para las reacciones de lactonización.

Principales métodos:

  • Descubrimiento de la enzima y aislamiento de la vía de la decarestrictina C1.
  • Ensayos bioquímicos para evaluar la actividad de DcsB y el alcance del sustrato.
  • Cristalografía de rayos X y modelado computacional para dilucidar el mecanismo catalítico.

Principales resultados:

  • Descubrimiento de la tioesterasa DcsB, una enzima que cataliza eficientemente las lactonizaciones de anillo medio.
  • DcsB exhibe una amplia promiscuidad de sustrato con precursores lineales de diferentes longitudes y sustituyentes.
  • Los análisis estructurales y computacionales revelaron la base molecular de la actividad catalítica de DcsB.

Conclusiones:

  • DcsB es una enzima altamente efectiva para la lactonización de anillo medio, superando los desafíos sintéticos.
  • El amplio alcance del sustrato de la enzima la convierte en un biocatalizador prometedor para diversas aplicaciones de síntesis de lactona.
  • Comprender el mecanismo de DcsB proporciona información sobre el control enzimático de las ciclizaciones desafiantes.