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Related Concept Videos

Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

3.2K
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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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.7K
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.
2.7K
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

3.7K
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
3.7K
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry01:29

Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry

6.5K
Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
6.5K
Pericyclic Reactions: Introduction01:17

Pericyclic Reactions: Introduction

10.8K
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.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic...
10.8K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.4K
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
2.4K

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A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species
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Enantioselective polyene cyclizations.

Chad N Ungarean1, Emma H Southgate, David Sarlah

  • 1Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA. sarlah@illinois.edu.

Organic & Biomolecular Chemistry
|May 5, 2016
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Summary

Enantioselective polyene cyclizations rapidly create complex molecules from simple starting materials. Recent advances enable precise synthesis of intricate polycyclic compounds and natural products.

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Area of Science:

  • Organic Chemistry
  • Synthetic Chemistry
  • Catalysis

Background:

  • Polyolefin cyclization is a key strategy for building molecular complexity.
  • Significant progress has been made in enantioselective methods over the past decade.
  • These methods transform prochiral polyenes into enantiomerically enriched polycyclic products.

Purpose of the Study:

  • To review recent advancements in enantioselective polyene cyclizations.
  • To highlight the application of these methods in synthesizing complex natural products.
  • To showcase the development of new catalytic systems for asymmetric synthesis.

Main Methods:

  • Review of literature on enantioselective polyene cyclizations.
  • Analysis of catalytic systems (e.g., transition metal catalysts, organocatalysts).
  • Discussion of substrate scope and reaction mechanisms.

Main Results:

  • Development of highly enantioselective cyclization reactions.
  • Successful application in the total synthesis of various complex natural products.
  • Emergence of novel catalytic strategies offering improved efficiency and selectivity.

Conclusions:

  • Enantioselective polyene cyclizations are a powerful and versatile synthetic tool.
  • Continued innovation in catalysis is driving the synthesis of complex molecules.
  • These methods are crucial for accessing challenging secondary metabolites with high stereochemical control.