Regioselective Synthesis of Pyrazoles and Isoxazoles with Cyclopropanated Side‐Chain

Pyrazoles and isoxazoles with cyclopropanated side‐chain were prepared by cyclization of cyclopropanated 1,3,5‐tricarbonyl compounds with hydrazine and hydroxylamine, respectively. The regioselectivity is influenced by the reaction conditions.     

Self‐Assembly of Highly Stable Zirconium(IV) Coordination Cages with Aggregation Induced Emission Molecular Rotors for Live‐Cell Imaging

The self‐assembly of highly stable zirconium(IV)‐based coordination cages with aggregation induced emission (AIE) molecular rotors for in vitro bio‐imaging is reported. The two coordination cages, NUS‐100 and NUS‐101, are assembled from the highly stable trinuclear zirconium vertices and two flexible carboxyl‐decorated tetraphenylethylene (TPE) spacers. Extensive experimental and theoretical results show that the emissive intensity of the coordination cages can be controlled by restricting the dynamics of AIE‐active molecular rotors though multiple external stimuli. Because the two coordination cages have excellent chemical stability in aqueous solutions (pH stability: 2–10) and impressive AIE characteristics contributed by the molecular rotors, they can be employed as novel biological fluorescent probes for in vitro live‐cell imaging.     

Aqueous Ring‐Opening Polymerization‐Induced Self‐Assembly (ROPISA) of N‐Carboxyanhydrides

Reported here is the first aqueous ring‐opening polymerization (ROP) of N‐carboxyanhydrides (NCAs) using α‐amino‐poly(ethylene oxide) as a macroinitiator to protect the NCA monomers from hydrolysis through spontaneous in situ self‐assembly (ISA). This ROPISA process affords well‐defined amphiphilic diblock copolymers that simultaneously form original needle‐like nanoparticles.     

Stereo‐ and Regioselective Synthesis of Tricyclic Spirolactones by Diastereoisomeric Differentiation of a Collective Key Precursor

A general, parallel, and collective synthesis of 5/5/5‐ and 5/5/6‐ring fusion topologies of tricyclic spiranoid lactones through the controlled cyclizations of easily accessible, common key precursors is described. The rapid composition of key cycloalkyl methylene precursors yielded an assembly of bicyclic diastereoisomeric iodolactones, which were individually converted into a wide range of tricyclic, angularly fused spiranoid lactones in a regioselective and stereodirected fashion through the diastereoisomeric differentiation of a collective key precursor. The critical stereochemical assignment of the bicyclic starting materials, as well as the tricyclic targets, was confirmed by X‐ray crystal structure determination.     

Regioselective Ring‐Opening of Amino Acid‐Derived Chiral Aziridines: an Easy Access to cis‐2,5‐Disubstituted Chiral Piperazines

An efficient four‐step synthetic strategy for cis‐2,5‐disubstituted chiral piperazines derived from amino‐acid‐based aziridines is described. The key steps in this strategy are the highly regioselective boron trifluoride diethyl etherate (BF₃ ⋅ OEt₂)‐mediated ring‐opening of less‐reactive N‐Ts chiral aziridines by α‐amino acid methyl ester hydrochloride followed by Mitsunobu cyclization. This protocol has been used in an attempt to construct the piperazine core framework of natural product (+)‐piperazinomycin.     

Influence of Metal,Ligand and Solvent on Supramolecular Polymerizations with Transition‐Metal Compounds: A Theoretical Study

The nature of intermolecular interactions governing supramolecular polymerizations is very important for controlling their cooperativity. In order to address this problem, supramolecular columns made of Pt^II and Pd^II complexes of oligo(phenylene ethynylene)‐based pyridine (OPE) and tetrazolylpyridine ligands (TEP) were investigated through the dispersion‐corrected PM6 method. Aromatic, CH–π, M–Cl and metallophilic interactions helped stabilize the supramolecules studied, and their geometries and associated cooperativities were in excellent agreement with experimental data. The OPE ligand and/or the presence of Pt^II led to stronger metallophilic interactions and also to cooperative supramolecular polymerizations, which clearly suggests that metallophilic interactions are a key factor for controlling cooperativity. The results indicate that sequential monomer addition is in general less spontaneous than the combination of two larger preformed stacks. The present theoretical investigations contribute to the further understanding of the relation between the thermodynamics of supramolecular polymerizations and the nature of different synthons.     

Self‐Assembly of Aggregation‐Induced‐Emission Molecules

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.     

Molecular Design,Circularly Polarized Luminescence,and Helical Self‐Assembly of Chiral Aggregation‐Induced Emission Molecules

Aggregation‐induced emission luminogens (AIEgens) are a new class of luminophors, which are non‐emissive in solution, but emit intensively upon aggregation. By properly designing the chemical structures of the AIEgens, their aggregation process can be tuned towards a desired direction to give diverse novel luminescent architectures of micelles, rods, and helical fibers. AIEgens represent a kind of promising building block for the fabrication of luminescent micro/nanostructures with controllable morphologies. In this review, we describe our recent work in this research area, focusing on the molecular design, circularly polarized luminescence properties, and helical self‐assembly behavior of AIEgens.     

Mechanistic Study of the Rhodium‐Catalyzed [3+2+2] Carbocyclization of Alkenylidenecyclopropanes with Alkynes

A systematic theoretical study has been performed on the recently reported Rh^I‐catalyzed [3+2+2] carbocyclization reactions between alkenylidenecyclopropanes (ACPs) and alkynes. With the aid of theoretical calculations, two possible mechanisms, that is, alkene‐carbometalation‐first and alkyne‐carbometalation‐first mechanisms, are examined in this study. In the oxidative addition step, the possibility of reaction on either the distal or proximal C? C bond of the cyclopropane group has been evaluated. The calculations indicate that the alkene‐activation‐first mechanism is more favored for the overall catalytic cycle. This mechanism involves four steps, that is, oxidative addition of the distal (rather than the proximal) C? C bond of cyclopropane group, alkene carbometalation, alkyne carbometalation, and reductive elimination. The rate‐determining step in the overall catalytic cycle is the carbometalation of the alkyne (i.e., the alkyne‐insertion step) and this step also determines the regioselectivity. Finally, the origin of the regioselectivity is determined by the steric effect (i.e., the steric crowding between the electron‐withdrawing group on alkyne and other ligands on the rhodium center) in the alkyne‐insertion step.     

Light‐Induced Reversible Self‐Assembly of Gold Nanoparticles Surface‐Immobilized with Coumarin Ligands

A novel light‐induced reversible self‐assembly (LIRSA) system is based on the reversible photodimerization and photocleavage of coumarin groups on the surface of gold nanoparticles (AuNPs) in THF solution. Facilitated by coumarin groups, light irradiation at 365 nm triggers the stable assembly of monodisperse AuNPs; the resulting self‐assembly system can be disassembled back to the disassembled state by a relatively short exposure to benign UV light. The reversible self‐assembly cycle can be repeated 4 times. A specific concentration range of coumarin ligand and the THF solvent were identified to be the two predominant factors that contribute to the LIRSA of AuNPs. This is the first successful application of reversible photodimerization based on a coumarin derivative in the field of AuNP LIRSA. This LIRSA system may provide unique opportunities for the photoregulated synthesis of many adjustable nanostructures and devices.     

Anion Controlled Supramolecular Self‐Assembly of Tetraprotonated Tris[2‐(benzylamino)ethyl]amine

The novel supramolecular assembly of composition [{(bz₃tren)H₄}⁴⁺ · (ReO₄)^— · 3(Cl)^—] resulted from the self‐organization of a mixture of tris[2‐(benzylamino)ethyl]amine (bz₃tren), HCl and NH₄ReO₄ at a molar ratio of 1:4.7:1 in methanol. The crystal architecture is characterized by stacks of repeating sandwich‐type building blocks that contain charge‐assisted N—H···O(Re) hydrogen bonds [N···O 2.81‐2.86Å] and weaker C—H···O(Re) interactions [C···O 3.11Å]. The stacks are further linked by N—H···Cl [N···Cl 3.03Å] and weaker C—H···Cl [C···Cl 3.47‐3.74Å] interactions into two‐dimensional layers bordered by the benzyl groups of the [(bz₃tren)H₄]⁴⁺ cations. Edge‐to‐face C—H···π interactions involving the aromatic rings occur within and between the layers. The protonation constants of bz₃tren in methanol were determined by potentiometric titration. The corresponding structures of the ligand in its different protonation states were calculated at the DFT‐level.     

Highly Regioselective 5-endo-tet Cyclization of 3,4-Epoxy Amines into 3-Hydroxypyrrolidines Catalyzed by La(OTf)3

Highly regioselective intramolecular aminolysis of 3,4-epoxy amines has been achieved. Key features of this reaction are (1) chemoselective activation of epoxides in the presence of unprotected aliphatic amines in the same molecules by a La(OTf)₃ catalyst and (2) excellent regioselectivity for anti-Baldwin 5-endo-tet cyclization. This reaction affords 3-hydroxy-2-alkylpyrrolidines stereospecifically in high yields. DFT calculations revealed that the regioselectivity might be attributed to distortion energies of epoxy amine substrates. The use of this reaction was demonstrated by the first enantioselective synthesis of an antispasmodic agent prifinium bromide.     

Stereo‐ and Regioselective Alkyne Hydrometallation with Gold(III) Hydrides

The hydroauration of internal and terminal alkynes by gold(III) hydride complexes [(C^N^C)AuH] was found to be mediated by radicals and proceeds by an unexpected binuclear outer‐sphere mechanism to cleanly form trans‐insertion products. Radical precursors such as azobisisobutyronitrile lead to a drastic rate enhancement. DFT calculations support the proposed radical mechanism, with very low activation barriers, and rule out mononuclear mechanistic alternatives. These alkyne hydroaurations are highly regio‐ and stereospecific for the formation of Z‐vinyl isomers, with Z/E ratios of >99:1 in most cases.     

Chemo‐ and Regioselective Rhodium(I)‐Catalyzed [2+2+2] Cycloaddition of Allenynes with Alkynes

A highly chemo‐ and regioselective partially intramolecular rhodium(I)‐catalyzed [2+2+2] cycloaddition of allenynes with alkynes is described. A range of diverse polysubstituted benzene derivatives could be synthesized in good to excellent yields, in which the allenynes served as synthetic equivalent to the diynes. A high regioselectivity could be observed when allenynes were treated with unsymmetrical alkynes.