For molecular architectures based on dynamic covalent chemistry (DCvC), strict preorganization is a paradigmatic concept and the generally accepted strategy for their rational design. This results in ...the creation of highly rigid building blocks which are expected to fulfill the ideal geometry of the assembly, coming at a price that small geometric mismatches result in unpredicted and/or unproductive reaction outcomes. In this study, we show that feet of a tripodal platform have a great influence on the assembly of tetrahedral organic cages based on boronate ester formation. The aryl benzyl ether-functionalized building blocks perform significantly better than their alkyl-functionalized equivalents. Experimentally and using density functional theory geometry optimization of the cage structures, we prove that unexpectedly, this is not due to solubility but because of the enhanced capability of the aryl benzyl ether-functionalized building blocks to fit the ideal geometry of the assembly. This introduces the concept of building block adaptability to overcome geometrical mismatches in DCvC systems.
Ascorbic acid (vitamin C) has been used as a radical initiator in a metal‐free direct CH arylation of (hetero)arenes. Starting from an aniline, the corresponding arenediazonium ion is generated in ...situ and immediately reduced by vitamin C to an aryl radical that undergoes a homolytic aromatic substitution with a (hetero)arene. Notably, neither heating nor irradiation is required. This procedure is mild, operationally simple, and constitutes a greener approach to arylation.
Vitamin C oupling: A catalytic amount of ascorbic acid acted as a radical initiator in a metal‐free direct CH arylation of arenes and heteroarenes with anilines (see scheme; Boc=tert‐butoxycarbonyl). The reaction requires no heating or irradiation, is operationally simple, and constitutes a greener approach to arylation.
A novel halogenation reaction from sulfonates catalyzed by iron(III) is described. The reaction can be performed as a stoichiometric or a catalytic version. This reaction provides a convenient ...strategy for the efficient access to structurally diverse secondary chlorides, bromides and iodides. The stereochemical course of the reaction is governed by the substrate and the experimental conditions. Secondary alcohols modified as quisylates or pysylates are substantially more reactive. Aliphatic quisylates proceed with overall inversion of configuration under catalytic conditions. Chemoselectivity in bismesylates was observed in favour of the secondary mesylate. Additionally, based on the experimental results, a possible catalytic cycle for the halogenation has been proposed.
Directional bonding strategies guide the design of complex molecular architectures, yet challenges arise due to emergent behavior. Rigid structures face geometric constraints and sensitivity to ...mismatches, hindering the efficient assembly of molecular organic cages (MOCs). Harnessing intramolecular non‐covalent interactions offers a promising solution, broadening geometrical possibilities and enhancing adaptability to boost assembly yields. However, identifying these interactions remains challenging, with their full potential sometimes latent until final assembly. This study explores these challenges by synthesizing boronic acid tripods with varied oxygen positions at the tripodal feet and investigating their role in assembling tetrahedral boronate MOCs. Our results reveal substantial differences in the assembly efficiency among tripods. While the building blocks with oxygen in the benzylic position relative to the central aromatic ring form the MOCs in high yields, those with the oxygen atom directly bound to the central aromatic ring, only yield traces. Through X‐ray crystallography and DFT analyses, we elucidate how intramolecular interactions profoundly influence the geometry of the building blocks and cages in a relay‐like fashion, highlighting the importance of considering intramolecular interactions in the rational design of (supra)molecular architectures.
Latent intramolecular non‐covalent interactions (NCIs) within the building blocks play a crucial role in the assembly of molecular organic cages (MOCs) via Dynamic Covalent Chemistry (DCC). These intramolecular interactions emerge from induced conformational restrictions during cage assembly, ultimately dictating the reaction outcome in a relay‐like fashion.
Abstract
This account describes our studies on the synthesis of natural products that contain cyclic ethers in their structures. An overview of the main methodologies is presented and several total ...syntheses developed by the group are described. We also discuss new applications based on the use of Prins and Nicolas reactions as key steps in the preparation of oxygenated heterocyclic compounds.
1 Introduction
1.1 Natural Sources and Biogenesis
2 Carbon–Oxygen Bond-Formation Approach
2.1 Intramolecular Opening of Epoxy Alcohols and Related Bromo Cyclizations
2.2 Intramolecular Hetero-Michael Reaction of Alkoxy γ-Benzoyloxy α,β-Unsaturated Esters
2.3 Intramolecular Nicholas Reaction
3 Ring-Closing Metathesis of Unsaturated Linear Ethers
4 Prins Cyclization Promoted by Iron(III) salts
4.1 General Strategy
4.2 Cyclization Using Alkynols and the Formation of Vinyl Halides
4.3 The Use of Trimethylsilyl and Electron-Withdrawing Substituents in the Synthesis of 2,6-Disubstituted Tetrahydropyrans
4.4 Catalytic Prins Cyclization
4.5 Synthesis of Oxepanes
5 Summary
The discovery of molecular organic cages (MOCs) is inhibited by the limited organic-chemical space of the building blocks designed to fulfill strict geometric requirements for efficient assembly. ...Using intramolecular attractive or repulsive non-covalent interactions to control the conformation of flexible systems can effectively augment the variety of building blocks, ultimately facilitating the exploration of new MOCs. In this study, we introduce a set of boronic acid tripods that were designed using rational design principles. Conformational control was induced by extending the tripod's arms by a 2,3-dimethylbenzene unit, leading to the efficient formation of a tetrapodal nanometer-sized boroxine cage. The new building block's versatility was demonstrated by performing cage metamorphosis upon adding an aromatic tetraol. This led to a quantitative boroxine-to-boronate transformation and a topological shift from tetrahedral to trigonal bipyramidal.
The conformational control of boronic acid building blocks allows efficient self-assembly into a tetrahedral boroxine cage. The nano-sized cage displays molecular metamorphosis, converting from a boroxine tetrapod to a boronate bipyramid.
A new approach to lauroxanes by a powerful and highly convergent methodology based on iterative use of Co2(CO)6-acetylenic complexes is described. The strategy employs an intermolecular Nicholas ...reaction to form unsaturated branched linear ethers, a ring closing metathesis to obtain the cobalt complex cyclic ethers, and an isomerization promoted by montmorillonite K-10. A short synthesis of cyclic ethers of seven-, eight-, and nine-membered rings is described. Additionally, the methodology is exemplified by the formal synthesis of (+)-laurencin, a red algae metabolite.
New organic-inorganic nanocomposites based on PVA, SiO
2
and SSA were prepared in a single step using a solution casting method, with the aim to improve the thermomechanical properties and ionic ...conductivity of PVA membranes. The structure, morphology, and properties of these membranes were characterized by Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water uptake (Wu) measurements and ionic conductivity measurements. The SAXS/WAXS analysis showed that the silica deposited in the form of small nanoparticles (∼ 10 nm) in the PVA composites and it also revealed an appreciable crystallinity of pristine PVA membrane and PVA/SiO
2
membranes (decreasing with increasing silica loading), and an amorphous structure of PVA/SSA and PVA/SSA/SiO
2
membranes with high SSA loadings. The thermal and mechanical stability of the nanocomposite membranes increased with the increasing silica loading, and silica also decreased the water uptake of membranes. As expected, the ionic conductivity increased with increasing content of the SSA crosslinker, which is a donor of the hydrophilic sulfonic groups. Some of the PVA/SSA/SiO
2
membranes had a good balance between stability in aqueous environment (water uptake), thermomechanical stability and ionic conductivity and could be potential candidates for proton exchange membranes (PEM) in fuel cells.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We report a new and efficient synthetic strategy that allows access to flexible and functionalized benzocyclotrimers under mild conditions and in few steps. The Negishi cross-coupling reaction was ...used for the C-C bond formation, whereas intramolecular O-alkylations provided the oxepane rings.
Call in the reinforcements: Intra‐receptor noncovalent interactions can enantioselectively cooperate with guest binding, thus triggering chiral discrimination. Such cooperativity is described and ...quantified for a simple synthetic system wherein an intra‐receptor hydrogen bond cooperates with a CH–π interaction exclusively formed with the D enantiomer of the guest, thus exemplifying reinforced chiral recognition (see picture).
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