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A General Base Condensation of Diynes to a Spirocyclopropenyl System
Jordan Holloway1, David L Cedeño, Richard C Reiter
1Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160.
Journal of the American Chemical Society
|June 28, 2007
Summary
This study reveals a novel spirocyclopropene synthesis from diynes using potassium tert-butoxide. The resulting compound is a stable organometallic eta2-olefin pentacarbonyl complex.
Area of Science:
- Organic Chemistry
- Organometallic Chemistry
Background:
- Cyclopropene compounds are strained cyclic molecules with unique reactivity.
- Spirocyclopropenes are a subclass of cyclopropenes featuring a spirocyclic structure.
- The synthesis of spirocyclopropenes is challenging, with few reported examples.
Purpose of the Study:
- To develop a new synthetic route to spirocyclopropene compounds.
- To characterize the intermediate radical anion and the final spirocyclopropene product.
- To explore the reactivity of the synthesized spirocyclopropene with organometallic precursors.
Main Methods:
- Reaction of 1,6-heptadiyne with potassium tert-butoxide and 18-crown-6 in THF at low temperature.
- Electron Paramagnetic Resonance (EPR) spectroscopy for radical anion characterization.
- Reduced pressure distillation for product isolation.
- Laser irradiation of tungsten hexacarbonyl with the spirocyclopropene.
Main Results:
- Formation of a green, EPR-active solution attributed to the anion radical of 7,14-di-trans-1,5-[14]annuldiyne.
- Color change to deep purple and loss of EPR activity upon warming.
- Isolation of spiro[2.6]nona-2,6,8-triene, a novel spirocyclopropene.
- Synthesis of a stable eta2-olefin pentacarbonyl complex via laser irradiation.
Conclusions:
- A general base condensation method for synthesizing spirocyclopropenyl systems from various diynes was established.
- The study reports the second known spirocyclopropene compound.
- The synthesized spirocyclopropene serves as a valuable precursor for stable organometallic complexes.
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01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
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.
01:28Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
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.
01:29Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
01:16Cycloaddition Reactions: Overview
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.
01:16Structure of Conjugated Dienes
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
01:32Aldehydes and Ketones with HCN: Cyanohydrin Formation Overview
Cyanohydrins are compounds that contain –CN and –OH groups on the same carbon atom. They are formed by the nucleophilic addition of the cyanide ions to the carbonyl group. Cyanide ions are highly basic and nucleophilic and can be generated from HCN under aqueous conditions. However, since HCN is a weak acid, the number of cyanide ions generated is very small. Hence, a small amount of base or KCN/NaCN is added to HCN to increase the concentration of the cyanide ions in the reaction mixture.