Aggregation-Induced Catalysis: Asymmetric Catalysis with Chiral Aggregates

Characterization of Chiral Thiophene Multilayer 3D Polymers with AIE Properties for Environmental Monitoring of Chromium Ions

This study reports the synthesis and characterization of novel thiophene-based multilayer 3D chiral polymers incorporating methoxy and octyloxy functional groups. These polymers exhibit unique fluorescence properties, including a pronounced aggregation-induced emission (AIE) phenomenon at a lower excitation wavelength than previously reported thiophene systems. Additionally, the polymers demonstrate remarkable sensitivity in detecting hexavalent chromium ions (Cr6+), a significant environmental pollutant. The interaction between the chiral polymers and Cr6+ ions leads to measurable changes in fluorescence, highlighting their potential for applications in environmental monitoring and biosensing. Importantly, these polymers are effective in actual environmental water, where they maintain their selectivity for Cr6+ ions despite the presence of competing metal ions. This enhanced selectivity further underscores their suitability for real-world applications. This work contributes to the field of chiral polymers and emphasizes their versatility in advanced sensing applications.

Stereospecific Radical Bromination of β-Aryl Alcohols with Thiourea Additives Through A Serendipitous Discovery of A 1,2-Aryl Migration

The development of new protocols for stereospecific and stereoselective halogenation transformations by mild reaction conditions is a highly desirable research target for the chemical and pharmaceutical industries. Following the straightforward methodology for directly transforming a wide scope of alcohols to alkyl bromides and chlorides using substoichiometric amounts of thioureas and N-halo succinimides (NXS) as a halogen source in a single step, we noticed that in apolar solvents bromination of chiral secondary alcohols did not produce the expected racemates. In this study, the stereochemical aspects of the bromination reaction were examined. Surprisingly, bromination of (±)-threo- or (±)-erythro-3-phenyl-2-butanols revealed a single diastereomeric brominated product with retention of configuration. The scope of these reactions was expanded on several β-aryl alcohols. During these studies, an unexpected stereospecific 1,2-migration of the phenyl group was shown to take place. The proposed mechanism of the 1,2-phenyl migration involves the formation of a spiro[2,5]octadienyl radical, which is then attacked by a bromide radical at any of the two cyclopropyl positions anti to the phenyl position, leading to products that retain the stereoisomeric configuration of the starting material.

P(═O)R2-Directed Asymmetric Catalytic C-H Olefination Leading to C-N Axially Chiral Targets

A novel P(═O)R2-directed asymmetric catalytic olefination has been developed, enabling efficient access to carbon-nitrogen axially chiral products with excellent yields (up to 92%) and enantioselectivity (up to 99% enantiomeric excess). The synergistic coordination of phosphine oxide functionality and l-pGlu-OH with the Pd metal center, serving as an efficient directing group and chiral ligand, was key to the success of this C-H functionalization system. The reaction demonstrated a broad substrate scope, yielding 33 distinct C-N axial products. The absolute configuration of the products was unambiguously confirmed via X-ray diffraction analysis. Additionally, three representative applications were showcased, involving reduction and oxidation to produce chiral phosphines and related derivatives. A plausible catalytic cycle mechanism has been proposed, supported by detailed experimental studies. Aggregates in the system were identified by aggregation-induced polarization experiments.

Straightforward Superbase-Mediated Reductive O-Phosphorylation of Aromatic and Heteroaromatic Ketones with Red Phosphorus in the Superbase Suspension KOH/DMSO(H2O)

It was shown for the first time that diaryl(hetaryl)ketones are capable of directly phosphorylating with red phosphorus in the superbase suspension KOH/DMSO(H2O) at 85 °C for 1.5 h to afford potassium bis(diaryl(hetaryl)methyl)phosphates that were earlier inaccessible in a yield of up to 45%. The ESR data demonstrate that unlike previously published phosphorylation with elemental phosphorus, this new phosphorylation reaction proceeds via a single electron transfer from polyphospide anions to diaryl(hetaryl)ketones. This is the first example of the C-O-P bond generation during the phosphorylation with elemental phosphorus in strongly basic media, which usually provides C-P bond formation.

Carbene-Catalyzed Phthalide Ether Functionalization for Discovering Chiral Phytovirucide that Specifically Targets Viral Nia Protein to Inhibit Proliferation

Plant diseases caused by vegetable viruses are an important threat to global food security, presenting a major challenge for the development of antiviral agrochemicals. Functional proteins of plant viruses play a crucial role in the viral life cycle, and targeted inhibition of these proteins has emerged as a promising strategy. However, the current discovery of antiviral small molecules is hampered by the limitations of synthetic approaches and the narrow range of targets. Herein, we report a practical application of organocatalysis for serving pesticide discovery that bears a unique molecular basis. An N-heterocyclic carbene-modulated reaction is first designed to asymmetrically functionalize diverse natural phenols with phthalides. Our designed method is capable of producing a series of new phthalidyl ethers under mild conditions with good yields, enantioselectivity, and functional group tolerance. Among these, compound (R)-3w exhibits excellent and enantioselectivity-preferred curative activity against potato virus Y (PVY). Mechanistically, it is proposed that (R)-3w interacts with the nuclear inclusion body A (Nia) protein of PVY at the His150 residue. This binding impairs Nia's function to cleavage polyprotein, thereby inhibiting formation of viral replication complex. The study provides insights into advancing synthetic protocol to facilitate agrochemical discovery, and our identified (R)-3w may serve as a potential lead for future research and development PVY-Nia inhibitors.

Enantiopure Turbo Chirality Targets in Tri-Propeller Blades: Design, Asymmetric Synthesis, and Computational Analysis

Enantiopure turbo chirality in small organic molecules, without other chiral elements, is a fascinating topic that has garnered significant interest within the chemical and materials science community. However, further research into and application of this concept have been severely limited by the lack of effective asymmetric tools. To date, only a few enantiomers of turbo chiral targets have been isolated, and these were obtained through physical separation using chiral HPLC, typically on milligram scales. In this work, we report the first asymmetric approach to enantiopure turbo chirality in the absence of other chiral elements such as central and axial chirality. This is demonstrated by assembling aromatic phosphine oxides, where three propeller-like groups are anchored to a P(O) center via three axes. Asymmetric induction was successfully carried out using a chiral sulfonimine auxiliary, with absolute configurations and conformations unambiguously determined by X-ray diffraction analysis. The resulting turbo frameworks exhibit three propellers arranged in either a clockwise (P,P,P) or counterclockwise (M,M,M) configuration. In these arrangements, the bulkier sides of the aromatic rings are oriented toward the oxygen atom of the P=O bond rather than in the opposite direction. Additionally, the orientational configuration is controlled by the sulfonimine auxiliary as well, showing that one of the Naph rings is pushed away from the auxiliary group (-CH2-NHSO2-tBu) of the phenyl ring. Computational studies were conducted on relative energies for the rotational barriers of a turbo target along the P=O axis and the transition pathway between two enantiomers, meeting our expectations. This work is expected to have a significant impact on the fields of chemistry, biomedicine, and materials science in the future.

Discovery of Staircase Chirality through the Design of Unnatural Amino Acid Derivatives

Chirality has garnered significant attention in the scientific community since its discovery by Louis Pasteur over a century ago. It has been showing a profound impact on chemical, biomedical, and materials sciences. Significant progress has been made in controlling molecular chirality, as evidenced by the several Nobel Prizes in chemistry awarded in this area, particularly for advancements in the asymmetric catalytic synthesis of molecules with central and axial chirality. However, the exploration of new types of chirality has been largely stagnant for more than half a century, likely due to the complexity and challenges inherent in this field. In this work, we present the discovery of a novel type of chirality-staircase chirality as inspired by the design and synthesis of unnatural amino acid derivatives. The architecture of staircase chirality is characterized by 2 symmetrical phenyl rings anchored by a naphthyl pier, with the rings asymmetrically displaced due to the influence of chiral auxiliaries at their para positions. This unique staircase chiral framework has been thoroughly characterized using spectroscopic techniques, with its absolute configuration definitively confirmed by x-ray diffraction analysis. Remarkably, one of the staircase molecules exhibits 4 distinct types of chirality: central, orientational, turbo, and staircase chirality, a combination that has not been previously documented in the literature. Computational studies using density functional theory (DFT) calculations were conducted to analyze the relative energies of individual staircase isomers, and the results are in agreement with our experimental findings. We believe that this discovery will open up a new research frontier in asymmetric synthesis and catalysis, with the potential to make a substantial impact on the fields of chemistry, medicine, and materials science.

Protodefluorinated Selectfluor® Aggregatively Activates Selectfluor® for Efficient Radical C(sp3)-H Fluorination Reactions

Efficient fluorination reactions are key in the late-stage functionalization of complex molecules in medicinal chemistry, in upgrading chemical feedstocks, and in materials science. Radical C(sp3)-H fluorinations using Selectfluor® - one of the most popular fluorination agents - allow to directly engage unactivated precursors under mild photochemical or thermal catalytic conditions. However, H-TEDA(BF4)2 to date is overlooked and discarded as waste, despite comprising 95% of the molecular weight of Selectfluor®. We demonstrate that the addition of H-TEDA(BF4)2 at the start of fluorination reactions markedly promotes their rates and accesses higher overall yields of fluorinated products (~3.3 × higher on average across the cases studied) than unpromoted reactions. Several case studies showcase generality of the promotor, for photochemical, photocatalytic and thermal radical fluorination reactions. Detailed mechanistic investigations reveal the key importance of aggregation changes in Selectfluor® and H-TEDA(BF4)2 to fill gaps of understanding in how radical C(sp3)-H fluorination reactions work. This study exemplifies an overlooked reaction waste product being upcycled for a useful application.

Amino Turbo Chirality and Its Asymmetric Control

A series of new targets containing 3 chiral elements of central, orientational, and turbo chirality have been designed and synthesized asymmetrically. The absolute configurations and conformations of these types of chirality were concurrently controlled by using chiral sulfonimine auxiliary and unambiguously determined by x-ray diffraction analysis. These targets include alpha unnatural amino acid derivatives, which may play an important role for drug design, discovery, and development. Three propellers of turbo framework are covalently connected to a chiral C(sp3) center via C(sp2)-C(sp3) bonding along with a C-N axis, while one of them is orientated away from the same carbon chiral center. The turbo or propeller chirality is characterized by 2 types of molecular arrangements of propellers, clockwise (PPP) and counterclockwise (MMM), respectively. The turbo stereogenicity was found to depend on the center chirality of sulfonimine auxiliary instead of the chiral C(sp3) center, i.e., (S)- and (R)-sulfinyl centers led to the asymmetric formation of PPP- and MMM-configurations, respectively. Computational studies were conducted on relative energies for rotational barriers of a turbo target along the C-N anchor and the transition pathway between 2 enantiomers meeting our experimental observations. This work is anticipated to have a broad impact on chemical, biomedical, and materials sciences in the future.

C(sp)-C(sp) Lever-Based Targets of Orientational Chirality: Design and Asymmetric Synthesis

In this study, the design and asymmetric synthesis of a series of chiral targets of orientational chirality were conducted by taking advantage of N-sulfinylimine-assisted nucleophilic addition and modified Sonogashira catalytic coupling systems. Orientational isomers were controlled completely using alkynyl/alkynyl levers [C(sp)-C(sp) axis] with absolute configuration assignment determined by X-ray structural analysis. The key structural element of the resulting orientational chirality is uniquely characterized by remote through-space blocking. Forty examples of multi-step synthesis were performed, with modest to good yields and excellent orientational selectivity. Several chiral orientational amino targets are attached with scaffolds of natural and medicinal products, showing potential pharmaceutical and medical applications in the future.

New multiple-layered 3D polymers showing aggregation-induced emission and polarization

An exceptional achiral and chiral multilayer 3D polymer has been created and controlled by uniform and distinct aromatic chromophore units that are multiply sandwiched by naphthyl berths. In order to put together this assembly, it was necessary to search for new catalytic Suzuki-Miyaura polycouplings among various catalytic systems, monomers, and catalysts. Gel Permeation Chromatography (GPC) was able to verify the presence of many framework layers. The resulting achiral and chiral polymers displayed notable optical characteristic.

Enantioselective synthesis of [1,1'-binaphthalene]-8,8'-diyl bis(diphenylphosphane) and its derivatives

Two 8,8' disubstituted binaphthyl ligands have been designed and synthesized in 3.1% and 11.4% overall yield, respectively. X-ray structure analysis demonstrated that a unique chiral microenvironment was created. With the assistance of a new aggregation-induced polarization (AIP) technology, chiral aggregates were determined as the fraction of polar solvent increased in the nonpolar/polar solvent system, which indicated their potential in modern asymmetric synthesis and catalysis.

Four-layer folding framework: design, GAP synthesis, and aggregation-induced emission

The design and synthesis of a type of [1 + 4 + 2] four-layer framework have been conducted by taking advantage of Suzuki-Miyaura cross-coupling and group-assisted purification (GAP) chemistry. The optimized coupling of double-layer diboronic esters with 1-bromo-naphth-2-yl phosphine oxides resulted in a series of multilayer folding targets, showing a broad scope of substrates and moderate to excellent yields. The final products were purified using group-assisted purification chemistry/technology, achieved simply by washing crude products with 95% EtOH without the use of chromatography and recrystallization. The structures were fully characterized and assigned by performing X-ray crystallographic analysis. UV-vis absorption, photoluminescence (PL), and aggregation-induced emission (AIE) were studied for the resulting multilayer folding products.