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01:17Thermal 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.
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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02:36Regioselectivity and Stereochemistry of Hydroboration
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A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
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01:29Diels–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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01:27Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation
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Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, β-ketoesters, or β-diketones) and α,β-unsaturated carbonyl acceptors. Named after Sir Robert Robinson, who discovered it, this reaction yields a six-membered ring with three new C–C bonds (two σ bonds and one π bond).
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01:18Frost Circles for Different Conjugated Systems
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The inscribed polygon method is consistent with Hückel’s 4n + 2 rule and helps to learn whether the given cyclic compound is aromatic or not. The compound is stable and aromatic if every bonding molecular orbital (MO) is completely filled with a pair of electrons. However, if the non-bonding or antibonding orbitals are filled with electrons, the compound is unstable and not aromatic. Consider the Frost circle diagrams for cycloalkenes containing 4 to 8 carbons.
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01:28Diels–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.
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Shape-Persistent Anthracene-Based Macrocycles Prepared by Reversible Boronic Ester Formation: Crystallization and
Shoma Kasahara1, Hironobu Hayashi2, Takayuki Okumura3
1Institute for Chemical Research, Kyoto University Gokasho, Uji, Kyoto, 611-0011, Japan.
Chempluschem
|March 2, 2025
Summary
Researchers developed a new method to synthesize shape-persistent macrocycles with tunable cavities. These molecules show promise for gas adsorption and self-assembly in nanoarchitectures.
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Area of Science:
- Supramolecular Chemistry
- Materials Science
Background:
- Shape-persistent macrocycles are of interest for applications in molecular recognition and nanoelectronics.
- Confined inner spaces within macrocycles are key to their unique properties.
Purpose of the Study:
- To develop an efficient synthesis for macrocycles with anthracene units.
- To investigate the structural and gas adsorption properties of these macrocycles.
Main Methods:
- Reversible boronic ester formation between 1,2-diols and boronic acids.
- Powder X-ray diffraction (PXRD) and single crystal X-ray analysis.
- Nitrogen (N2) gas adsorption measurements.
Main Results:
- Template-free synthesis yielded macrocycles with internal cavities from 11 Å to 20 Å.
- Crystallinity was maintained after solvent removal and annealing.
- A macrocycle with phenyl linkers exhibited pseudo-nanocapsule behavior and superior N2 adsorption.
Conclusions:
- A robust synthesis strategy for shape-persistent macrocycles was established.
- These macrocycles have potential for gas adsorption and self-assembled nanoarchitectures.
- The phenyl-linked macrocycle demonstrates significant promise for advanced material applications.