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The synthesis of a new bis-BF2tetrafluorobenzo-[α]-fused BOPYPY dye from 4,5,6,7-tetrafluoroisoindole and 2-hydrazinopyrazine is reported. The regioselectivity of nucleophilic substitution reactions at the periphery of the tetrafluorinated BOPYPY and its α-bromo derivative were investigated using N-, O-, S-, and C-based nucleophiles. Among the aromatic fluorine atoms, the F2atom is consistently regioselectively substituted, except when the α-position contains a thiophenol group; in this case, F4is substituted instead due to stabilizing π–π-stacking between the two aromatic groups. The α-bromo BOPYPY derivative also reacts under Stille cross-coupling reaction conditions to produce the corresponding α-substituted product. The spectroscopic properties of these new fluorinated BOPYPYs were investigated and compared with nonfluorinated analogs.

We report an enantioselective synthesis of cyclic ketones with full substitutions at the α-positions in a highly diastereoselective manner. Our method is achieved by subjecting substrate motifs in 2-allyloxyenones to chiral organomagnesium reagents, which trigger the Claisen rearrangement upon direct 1,2-carbonyl addition. The observed diastereoselectivity of the allyl migration is proposed to originate from the intramolecular chelation of the magnesium alkoxide to the allyloxy moiety.

[HCo(CO)x(bisphosphine)](BF4), x= 1–3, is a highly active hydroformylation catalyst system, especially for internal branched alkenes. In situ infrared spectroscopy (IR), electron paramagnetic resonance (EPR), and nuclear magnetic resonance studies support the proposed catalyst formulation. IR studies reveal the formation of a dicationic Co(I) paramagnetic CO-bridged dimer, [Co2(μ-CO)2(CO)(bisphosphine)2]2+, at lower temperatures formed from the reaction of two catalyst complexes via the elimination of H2. DFT studies indicate a dimer structure with square-pyramidal and tetrahedral cobalt centers. This monomer–dimer equilibrium is analogous to that seen for HCo(CO)4, reacting to eliminate H2and form Co2(CO)8. EPR studies on the catalyst show a high-spin (S= 3/2) Co(II) complex. Reaction studies are presented that support the cationic Co(II) bisphosphine catalyst as the catalyst species present in this system and minimize the possible role of neutral Co(I) species, HCo(CO)4or HCo(CO)3(phosphine), as catalysts.

We describe a new synthetic reaction that generates all-carbon bis-quaternary centers at the opposing side of α-carbons in cyclohexanone with four different substituents in a controlled manner. Catalyzed by Cu(MeCN)4BF4salt, this chemistry is proposed to proceed via an intermediacy of unsymmetrical O-allyl oxyallyl cations, which undergo a sequence of regioselective nucleophilic addition with substituted indoles and diastereoselective Claisen rearrangement in a single synthetic operation. The stereochemical outcome of the products features the cisdiastereorelationship between the two aryl groups at the α,α′-positions.

A family of coumarin–enamine chemodosimeters is evaluated for their potential use as fluorescent molecular probes for multiple analytes [cadmium(II), cobalt(II), copper(II), iron(II), nickel(II), lead(II), and zinc(II)], as their chloride and acetate salts. These fluorophores displayed excellent optical spectroscopic modulation when exposed to ion pairs with different Lewis acidic and basic properties in dimethyl sulfoxide (DMSO). The chemodosimeters were designed to undergo excited-state intramolecular proton transfer (ESIPT), which leads to significant Stokes shifts (ca. 225 nm) and lower-energy fluorescence emission (ca. 575 nm). A more basic anion, e.g., acetate, inhibited the ESIPT mechanism by deprotonation of the enol, producing a binding pocket (N^O–chelate) that can coordinate to an appropriate metal ion. Coordination of the metal ions enhances the fluorescent intensity via the chelation-enhanced fluorescence emission mechanism. Subjecting the spectroscopic data to linear discriminant analysis provided insights into the source of these systems’ markedly different behavior toward ion pairs, despite the subtle structural differences in the organic framework. These compounds are examples of versatile, low-molecular-weight, dual-channel fluorescent sensors for ion-pair recognition. This study paves the way for using these probes as practical components of a sensing array for different metal ions andtheir respective anions.

The intermediacy of metallacyclobutadienes as part of a [2 + 2]/retro-[2 + 2] cycloaddition-based mechanism is a well-established paradigm in alkyne metathesis with alternative species viewed as off-cycle decomposition products that interfere with efficient product formation. Recent work has shown that the exclusive intermediate isolated from a siloxide podand-supported molybdenum-based catalyst was not the expected metallacyclobutadiene but instead a dynamic metallatetrahedrane. Despite their paucity in the chemical literature, theoretical work has shown these species to be thermodynamically more stable as well as having modest barriers for cycloaddition. Consequentially, we report the synthesis of a library of group VI alkylidynes as well as the roles metal identity, ligand flexibility, secondary coordination sphere, and substrate identity all have on isolable intermediates. Furthermore, we report the disparities in catalyst competency as a function of ligand sterics and metal choice. Dispersion-corrected DFT calculations are used to shed light on the mechanism and role of ligand and metal on the intermediacy of metallacyclobutadiene and metallatetrahedrane as well as their implications to alkyne metathesis.

Fluoroalkenes serve as bioisosteres to peptide bonds and are resistant to hydrolytic enzymes in vivo. Currently, α-fluoro-α,β-unsaturated carbonyl compounds are readily accessible via general synthetic methods; however, β-fluoro-α,β-unsaturated carbonyl groups are more challenging to construct. To address this need, we have designed a reagent, morpholine 3,3,3-trifluoropropanamide, that creates (E)-β-fluoro-α,β-unsaturated amides upon the addition of many commonly used Grignard reagents. Reactions with this reagent enable a high level of stereocontrol in the fluoroalkene product.

Triphenylsiloxide is one of the most successful ancillary ligands for Mo(VI)-alkyne metathesis catalysts. It was proposed that flexible siloxide ligands allow Mo–O–Si bond angles to modulate the electrophilicity of Mo≡C and thereby promote the catalysis. Introduction of a siloxide podand ligand allowed elucidation of the effect of ligand flexibility and Mo–O–Si angles on the electrophilicity of Mo≡C. It also allowed for the isolation of a rare metallatetrahedrane of Mo(VI) which was found to be dynamic in solution.

Controlled polymerization for the synthesis of structurally precise conjugated polymers remains a challenging problem in polymer chemistry. Catalyst-transfer polymerization (CTP) based on Pd-catalyzed Suzuki–Miyaura cross-coupling is one of the promising approaches toward solving this challenge. Recent introduction of N-methyliminodiacetic acid (MIDA) boronates as monomers for Suzuki–Miyaura CTP has extended this approach toward a broader variety of monomer structures and led to improved control over the polymerization, particularly for heteroaromatic systems (such as thiophenes). Previously, we found that MIDA boronate monomer polymerization could be facilitated by Ag+-mediated reaction conditions due to shifting the Pd catalytic cycle toward a more efficient oxo-Pd transmetalation pathway where MIDA boronates could participate in transmetalation directly without prior hydrolysis to boronic acid. In this work, we continued studying this novel process and investigated the dual role of the MIDA boronate functional group in the case of less reactive fluorenyl (and potentially other all-carbon aromatic systems) monomers. With such monomers, the MIDA boronate group enables the controlled polymerization but also produces a hydrolysis byproduct, hindering the polymerization. We also investigated the role of Ag+in counteracting this hindering effect. Steric bulkiness of the MIDA boronate functional group may also slow down the Suzuki–Miyaura CTP process. These complications could reduce the synthetic value of MIDA boronate monomers in Suzuki–Miyaura CTP, although better understanding of these implications and a proper choice of polymerization conditions and catalytic initiators could to some extent mitigate such problems. As part of this work, we also uncovered a “critical length” phenomenon, which results in a dual molecular weight distribution of the resulting conjugated polymer, both with MIDA boronate and boronic acid monomers. This phenomenon could account for the experimentally observed loss of polymerization control beyond formation of the polymer chains of a certain “critical length”, even despite the formally “living” nature of the polymer chains. The generality of this phenomenon and whether it is restricted to using Pd catalytic systems based on Buchwald-type phosphine ligands remain to be studied. Overall, these new findings paint a sophisticated picture of the Suzuki–Miyaura CTP process with MIDA boronate monomers where the mere presence of a Pd center on the polymer chain is not sufficient to sustain the polymerization (even if a chain could be considered “living” in the sense of possessing a Pd center), and the choice of the phosphine ligand on the Pd center is an effective tool to overcome the “critical length” restriction.

A new synthetic method to build aryl-fused 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) is reported. The intramolecular cyclization step was completed in a short time (1–2 h) and in high yields (>90%), due to the intrinsic rigid structural conformation of the precursor BODIPY and the high reactivity of its 1,7-bromo groups. The [a]phenanthrene-fused BODIPYs 4a–cwere characterized by NMR spectroscopy, HRMS, DFT calculations, and, in the case of 4a, by X-ray crystallography. Spectroscopic studies show that 4a–cstrongly absorb and emit in the NIR spectral region, in the range 642–701 nm. In addition, BODIPYs 4band 4cexhibit no toxicity in the light or dark in HEp2 cells and accumulate intracellularly in a time-dependent manner, mainly in the cell endoplasmic reticulum. These results suggest the potential use of [a]phenanthrene-fused BODIPYs as NIR bioimaging probes.

A series of trivalent lanthanide hydroxysulfates, Ln(OH)SO4, (Ln = Pr through Yb, except radioactive Pm) has been synthesized via hydrothermal methods from Ln2(SO4)3·8H2O by reaction with aqueous NaOH at 170 °C in Teflon lined Parr steel autoclaves, and were characterized by single crystal X-ray diffraction and FT-IR spectroscopy. Two types of arrangements were found in the solid state. The lighter (Ln = Pr−Nd, Sm−Gd) and heavier lanthanide(III) hydroxysulfates (Tb−Yb) are each isostructural. Both structure types exhibit the monoclinic space group P21/n, but the unit cell content is doubled with two crystallographically distinct LnO8polyhedra for the heavier lanthanide compounds. The lighter complexes maintain the coordination number 9, forming a three-dimensional extended lattice. The heavier counterparts exhibit the coordination number 8, and arrange as infinite columns of two crystallographically different LnO8polyhedra, while extending along the “c” axis. These columns of LnO8polyhedra are surrounded and separated by six columns of sulfate ions, also elongating in the “c” direction. The rigid sulfate entities seem to obstruct the closing in of the lighter LnO9polyhedra, and show an inclining degree of torsion into the “ac” layers. The crystal lattice of the lighter 4f complexes can sufficiently withstand the tension buildup, caused by the decreasing Ln3+radius, up to Gd(OH)SO4. The energy profile of this structural arrangement then seems to exceed levels at which this structure type is favorable. The lattice arrangement of the heavier Ln-analogues seems to offer a lower energy profile. This appears to be the preferred arrangement for the heavier lanthanide hydroxysulfates, whose crystal lattice exhibits more flexibility, as the coordination sphere of these analogues is less crowded. The IR absorbance frequencies of the hydroxide ligands correlate as a function of the Ln3+ionic radius. This corresponds well with the X-ray single crystal analysis data.

11,13-Dehydro seco-guaianolides, a particular type of sesquiterpene lactones, were synthesized from the commercially available α-santonin (11) using a facile strategy involving a high-yielding photochemical reaction. Natural products 10and 17from Artemisia gorgonumwere synthesized in good yields. Specifically, compound 10was obtained in five steps with an overall yield of 17%. The sesquiterpene lactones were tested in the etiolated wheat coleoptile bioassay, and the most active compounds were assayed on standard target species. Guaianolide 13showed the highest phytotoxic activities when compared with the known herbicide Logran.

An efficient synthesis of boron-functionalized cyclic BODIPY–Gly conjugates, using commercially available N-protected glycine amino acids and a BF2–BODIPY moiety as starting materials, is reported. The existence of two conformers (up and down) is revealed through comprehensive DFT calculations and 1H and 11B NMR analyses. The experimental and computational results indicate that all BODIPYs are stable in aqueous solutions at neutral pH and that Fmoc-BODIPY (4) is more stable than Ac-BODIPY (6) in the presence of trifluoroacetic acid (TFA). In part due to their enhanced rigidity, all BODIPY–Gly conjugates display increased fluorescence quantum yields (0.6 < Φ < 0.9) relative to the corresponding BF2–BODIPY, making them excellent candidates for fluorescence imaging applications.

Size selective synthesis of large cycloparaphenyleneacetylene carbon nanohoops was achieved using alkyne metathesis. The large nanohoops were stable in ambient conditions due to their reduced strain. The nanohoops exhibited blue fluorescence with high quantum yields.

An expedient synthesis of tetrahydroindoles and tetrahydrocyclopenta[b]pyrroles, highlighted by Brønsted acid catalyzed formal [2 + 2 + 1] annulation reaction, is reported. Using three readily accessible reaction components, i.e., an electrophilic species in silyloxyallyl cations and two distinct nucleophiles in silylenol ethers and amines, our chemistry enables the assembly and functionalization of these biologically important N-heterocycles in a highly modular manner.

A series of five boron dipyrromethene (BODIPY) bioconjugates containing an epidermal growth factor receptor (EGFR)-targeted pegylated LARLLT peptide and/or a glucose or biotin ethylene diamine group were synthesized, and the binding capability of the new conjugates to the extracellular domain of EGFR was investigated using molecular modeling, surface plasmon resonance, fluorescence microscopy, competitive binding assays, and animal studies. The BODIPY conjugates with a LARLLT peptide were found to bind specifically to EGFR, whereas those lacking the peptide bound weakly and nonspecifically. All BODIPY conjugates showed low cytotoxicity (IC50> 94 μM) in HT-29 cells, both in the dark and upon light activation (1.5 J/cm2). Studies of nude mice bearing subcutaneous human HT-29 xenografts revealed that only BODIPY conjugates bearing the LARLLT peptide showed tumor localization 24 h after intravenous administration. The results of our studies demonstrate that BODIPY bioconjugates bearing the EGFR-targeting peptide 3PEG-LARLLT show promise as near-IR fluorescent imaging agents for colon cancers overexpressing EGFR.

Eragrostis plana(Nees) is an allelopathic plant with invasive potential in South American pastures. To isolate and identify phytotoxic compounds from leaves and roots of E. plana, a bioassay-directed isolation of the bioactive constituents was performed. This is the first report on a new diterpene carbon skeleton, neocassane, and of three new neocassane diterpenes, neocassa-1,12(13),15-triene-3,14-dione, 1; 19-norneocassa-1,12(13),15-triene-3,14-dione, 2; and 14-hydroxyneocassa-1,12(17),15-triene-3-one, 3, identified from the roots. Compounds 1, 2, and 3inhibited the growth of duckweed by 50% at concentrations of 109 ± 28, 200 ± 37, and 59 ± 15 μM, respectively. Compound 2was fungicidal to Colletotrichum fragariae, Colletotrichum acutatum, and Colletotrichum gloeosporioides.The compounds identified here could explain the allelopathy of E. plana. The description of the newly discovered compounds, besides contributing to the chemical characterization of the species, may be the first step in the study of the potential of these compounds as bioherbicides.

Fluorescent small molecules enable researchers and clinicians to visualize biological events in living cells, tissues, and organs in real time. Herein, the focus is on the structure and properties of the relatively rare benzo[a]xanthenes that exhibit enhanced steric and electronic interactions due to their annulated structures. Three types of fluorophores were synthesized: (i) pH- and solvent-dependent seminaphthorhodafluors, (ii) pH- and solvent-independent seminaphthorhodafluors, and (iii) pH-independent but solvent-sensitive seminaphthorhodamines. The probes exhibited promising far-red to near-infrared (NIR) emission, large Stoke shifts, broad full width at half-maximum (fwhm), relatively high quantum yields, and utility in immunofluorescence staining. Deviation of the π-system from planarity due to changes in the fluorophore ionization state resulted in fluorescence properties that are atypical of common xanthene dyes.

A novel and straightforward strategy for boron functionalization in boron dipyrromethenes (BODIPYs) is developed. In particular, this synthetic strategy provides new possibilities for the synthesis of sp2N-substituted (B-NCS and -NCO), benzotriazole- and trifluoroacetamide-substituted BODIPYs that were hitherto unknown. These new BODIPYs display an array of highly desirable photophysical properties (0.04 < Φf< 0.86), paving the road for further investigations in material applications.

Kadsuraols A–C (1–3), which are tetrahydrocyclobutaphenanthrofuranone-type lignans with a new carbon skeleton comprising a four-membered ring across C-1′–C-8, have been isolated from the roots of Kadsura longipedunculata. Their structures and absolute configurations were unambiguously determined using nuclear magnetic resonance, X-ray diffraction crystallography, DP4+ calculations, and computed and experimental electronic circular dichroism spectra. Kadsuraol C (3) exhibited hepatoprotective activity against N-acetyl-p-aminophenol (APAP)-induced toxicity. The compounds showed no cytotoxicity at 10 μM in a zone assay.

Anthracene-bridged dinuclear rhenium complexes are reported for electrocatalytic carbon dioxide (CO2) reduction to carbon monoxide (CO). Related by hindered rotation of each rhenium active site to either side of the anthracene bridge, cisand transconformers have been isolated and characterized. Electrochemical studies reveal distinct mechanisms, whereby the cisconformer operates via cooperative bimetallic CO2activation and conversion and the transconformer reduces CO2through well-established single-site and bimolecular pathways analogous to Re(bpy)(CO)3Cl. Higher turnover frequencies are observed for the cisconformer (35.3 s–1) relative to the transconformer (22.9 s–1), with both outperforming Re(bpy)(CO)3Cl (11.1 s–1). Notably, at low applied potentials, the cisconformer does not catalyze the reductive disproportionation of CO2to CO and CO32–in contrast to the transconformer and mononuclear catalyst, demonstrating that the orientation of active sites and structure of the dinuclear ciscomplex dictate an alternative catalytic pathway. Further, UV–vis spectroelectrochemical experiments demonstrate that the anthracene bridge prevents intramolecular formation of a deactivated Re–Re-bonded dimer. Indeed, the cisconformer also avoids intermolecular Re–Re bond formation.

A series of (E,Z)-ethenyl- and ethynyl-linked boron dipyrromethene (BODIPY) dimers were synthesized in 23–34% yields by condensation of pyrroles with the corresponding bis-benzaldehydes, followed by oxidation and boron complexation. The BODIPY dimers were characterized by 1H, 13C, and 11B NMR spectroscopy, high-resolution mass spectrometry, and, in the cases of 1b, 2, and 3, by X-ray crystallography. The spectroscopic properties for this series of dimers were investigated in tetrahydrofuran solutions, and very similar absorption and emission profiles were observed for all dimers. Density functional theory calculations show minimal conjugation between the two BODIPY units in the dimers, as a result of the large dihedral angle between the BODIPYs and the linker. The (E)-ethenyl-linked dimer 1ashowed the highest fluorescence quantum yield of all dimers investigated in this study.