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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom, respectively.
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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.
Nomenclature of Alkynes02:39

Nomenclature of Alkynes

Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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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Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of &#945;-Imino &#947;-Lactones and Alkylidene Pyrazolones
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1,8-Pyrenylene-ethynylene macrocycles.

Gandikota Venkataramana1, Prateek Dongare, Louise N Dawe

  • 1Department of Chemistry, Memorial University, St. John's, NL, A1B 3X7, Canada.

Organic Letters
|March 31, 2011
PubMed
Summary

Researchers developed a regioselective synthesis for pyrene macrocycles. These macrocycles show minimal ring current and form dimers capable of intercalating small molecules.

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Area of Science:

  • Organic synthesis
  • Supramolecular chemistry
  • Materials science

Background:

  • Pyrene derivatives are valuable building blocks in organic electronics and supramolecular chemistry.
  • Macrocyclic compounds offer unique structural and electronic properties for molecular recognition and host-guest chemistry.

Purpose of the Study:

  • To develop a regioselective synthetic route to 1,8-dibromo-4,5-dialkoxypyrenes.
  • To synthesize and characterize novel 1,8-pyrenylene-ethynylene macrocycles.
  • To investigate the electronic properties and self-assembly behavior of these macrocycles.

Main Methods:

  • Regioselective bromination of dialkoxypyrenes.
  • Sonogashira cross-coupling reactions for macrocyclization.
  • Nuclear Magnetic Resonance (NMR) spectroscopy for structural elucidation.
  • Nuclear Independent Chemical Shift (NICS) calculations for electronic properties.
  • UV-visible spectroscopy for aggregation studies.

Main Results:

  • A concise and highly regioselective synthesis of 1,8-dibromo-4,5-dialkoxypyrenes was achieved.
  • Several 1,8-pyrenylene-ethynylene macrocycles were successfully synthesized.
  • (1)H NMR data and NICS calculations revealed minimal to no macrocyclic ring current.
  • UV-visible studies showed no aggregation at low concentrations.
  • Compound 8b demonstrated dimer formation with voids suitable for small molecule intercalation in the solid state.

Conclusions:

  • The developed synthetic strategy provides efficient access to functionalized pyrene macrocycles.
  • The synthesized macrocycles exhibit unique electronic properties, including suppressed ring current.
  • The observed dimer formation in compound 8b suggests potential applications in host-guest chemistry and molecular sensing.