6-membered Ring Research Articles

Effect of Adding Phosphorus on Crystal Structure of W-V-Nb Complex Oxide and Catalytic Selective Oxidation of Acrolein.

The changes in the crystal structure of the W-V-Nb complex oxide with phosphorus addition to the hydrothermal synthesis process are investigated. The effect of the constituent units and crystal structure of phosphorus-added W-V-Nb complex oxide catalysts on the activity and selectivity for selective oxidation of acrolein is discussed. Phosphorus addition to the hydrothermal synthesis process promotes the formation of orthorhombic and trigonal W-V-Nb complex oxides. Orthorhombic and trigonal W-V-Nb complex oxide catalysts give higher acrylic acid selectivity in acrolein oxidation compared to poorly crystalline catalysts that only have {M6O21} pentagonal units and 7-membered rings.

Enhancing Aromaticity of Alkenylbenzenes May Decrease Their Metabolic Activation and Reduce Their Potential Cytotoxicity: Lessons Learnt from the Investigation of Myristicin and Elemicin.

Metabolic activation studies of lead compounds are a crucial step in drug development and offer a key consideration during rational drug design. Myristicin (MRS) and elemicin (ELM), natural products belonging to alkenylbenzenes, share the backbone of 1-allyl-3-methoxybenzene. The backbone fuses with a methylenedioxy five-membered ring in MRS, while ELM is connected with two adjacent methoxy groups. ELM displayed powerful ability to induce cytotoxicity in cultured primary hepatocytes relative to MRS. Additionally, ELM exhibited superior efficiency in metabolic activation by CYP3A4, resulting in the formation of reactive metabolites carbonium ion, epoxides, and α,β-unsaturated ketone. Quantum chemical calculation and molecular dynamic studies revealed that the fused methylenedioxy 5-membered ring enhances the aromaticity of MRS, which affects the interaction between the allyl side chain and the heme for metabolic activation by the π-π stacking interaction with the aromatic amino acid residues of the host enzyme.

Dissociation Without Detonation: A DFT Analysis of the Thermally Induced Fragmentation of Binary Sulfur-Nitrogen Rings and Cages.

Potential thermal dissociation pathways available to binary sulfur nitrides have been explored by density functional theory methods, and the results interpreted in terms of their known thermochemical behavior. The cyclic cation/anion pair S3N3± both undergo concerted (4 + 2) cycloreversions to afford the 3-membered thiadiazirine ring c-NSN and, respectively, the SNS± cation/anions. A similar pathway has been identified for S4N2, leading to S3 and c-NSN. More complex multistep routes for the elimination of c-NSN have been identified for the bicyclic cation/anion pair S4N5±, as well as for the neutral cage structures S4N4 and S5N6. For the S4N5+ cation a transition state for competing skeletal scrambling via a 1,3-nitrogen σ-bond shift has been located. For the multiply charged cations S3N22+ and S4N42+, dissociation mechanisms are driven by charge repulsion effects, affording SNS+/SN+ and S3N3+/SN+ respectively. Channels leading to loss of NS+ from the cyclic cation species S4N3+ and S5N5+ have also been examined, and the possible role of open-chain and cyclic S3N2-based intermediates in the formation of S2N2 during the thermal cracking of S4N4 over silver wool is explored.

Fused Hexabenzocoronene-Porphyrin Conjugates with Tailorable Excited-State Lifetimes.

A new clear-cut strategy for fusing N-heterocyclic and carbon-pure systems is introduced en route to a versatile platform of multi-purpose tetrapyrrolic chromophores. In particular, three novel C-C bond-fused porphyrin-hexabenzocoronene (HBC) conjugates were synthesized under oxidative cyclodehydrogenation conditions, starting from tailor-made nickel porphyrin precursors. The fusion of the individual aromatic systems via 5-membered rings led to highly soluble π-extended porphyrins in excellent yields. The resulting porphyrin-HBC conjugates exhibit absorption cross-sections that are of interdisciplinary interest in the ever-growing field of organic photovoltaics and near-infrared (NIR) dyes. Quantum chemical calculations show that the newly formed 5-membered rings induce biradicaloid character in the porphyrin core, which has a strong impact on excited state lifetimes. This is confirmed by a thorough optoelectronic and time-resolved characterization in order to understand these unique features better. Broadened absorption characteristics go hand-in-hand with short-lived excited states with up to six orders of magnitude faster decay rates.

N-Doped and Bowl-Shaped Azabenzo[3,4]azulenofluorene: Synthesis and Characterization of Bridged Aza-Triarylamines.

Triarylamines are frequently employed as electron donor functional groups in a variety of organic electronic materials. We herein report the synthesis and in-depth characterisation of aza-analogues of fully bridged triarylamines, consisting of 5-, 6- and 7-membered rings. The impact of nitrogen doping and π-extension on the structural, electronic and optical-properties of these contorted heteroaromatic PAHs is thoroughly investigated and paves the way for an improved understanding of the structure-property relationships.

Tuning ZSM-22 zeolite through NH4F etching enables enhanced performance and tailored product distribution in n-alkane isomerization for sustainable aviation fuels

Isomerization of n-alkane remains a significant strategy for producing high-quality sustainable aviation fuels (SAF). Improving zeolite catalyst performance and optimizing iso-product distribution to meet the SAF specification are still challenging. As the limitation mainly originated from the strict shape selectivity of the microporous zeolite structure, feasible methods were highly demanded. In this work, the NH4F etching approach was utilized to controllably regulate the framework structure of ZSM-22 zeolite, leading to the rational variation in the crystallinity, porosity, morphology, and acidity, which were closely correlated with the etching severity. Compared to the elliptical 10-membered ring micropore mouths of the parent zeolite, the micropore mouths of the etched ZSM-22 zeolite tended to be circular, as observed by HRTEM and strongly supported by Raman, realizing the regulation of zeolite structure. For n-decane isomerization, the etched catalysts exhibited a considerable increase in catalytic performance, surpassing the parent Pt/ZSM-22 catalyst and the highest isomer yield of 82.1% at the conversion of 91.4% was achieved. The optimized iso-product distribution with approximatively equal amounts of several mono-branched isomers and much higher contributions of the originally disfavored isomers was also observed due to the tuned shape selectivity and the balanced bifunctionality. This work presented an efficient method to design zeolite catalysts for linear paraffin isomerization beyond the limit set by the zeolite structure and shape selectivity that meets the strict standard specification for the freezing point of the SAF.

Schleyer hyperconjugative aromaticity in indene scaffolds

In the present research, the Schleyer hyperconjugative aromaticity was used to enhance the aromaticity of indene scaffolds. The first section of the research focused on examining the thermodynamic stability and electronic characteristics of the four structural isomers of indene. Results indicate that 1H-indene scaffolds are the most stable thermodynamic isomers of indene derivatives exceeding 100 kJ/mol. The hierarchy of stability is as follows: 1H-indenes > 2H-indenes > 5H-indenes > 4H-indenes. The aromaticity of 5- and 6-membered rings in the isomeric structures was investigated using the B3LYP/6–311 + G(d,p) method in the second section of the study. The hyperconjugative aromaticity of 5MR and 6MR was assessed using the harmonic oscillator model of aromaticity index, Bird index, Shannon index, aromatic fluctuation index, and the nucleus independent chemical shift. The results reveal that introducing electron-donating groups on 6MR enhances the aromaticity of 5MR. Moreover, adding two fluorine atoms on the Csp3 site negatively affects the aromaticity and induces antiaromaticity in the indene scaffold. Based on aromaticity data, the order of increasing aromaticity in the presence of different groups is F < CH3 < H < SiH3 < GeH3 < Si(CH3)3 < Ge(CH3)3. The extent of the Schleyer hyperconjugation interaction was also quantified using the E(2) parameter obtained from the NBO calculations.

High-Pressure Rate Rules for Ether Alkylperoxy Radical Isomerization.

The first isomerization reaction of an alkylperoxy (RO2) radical holds significant importance in low-temperature oxidation, as it governs the branching ratios of the hydroperoxyalkyl (QOOH) radicals, which influence the competition between the chain-propagation and chain-branching reactions. In this study, we systematically calculated high-pressure rate rules for the RO2 isomerization reaction of monoethers, exploring 5-, 6-, 7-, and 8-membered ring transition states. Primary, secondary, and tertiary carbon sites, where both the abstracting peroxy group and the abstracted hydrogen are located, were considered, with particular emphasis on distinguishing between secondary carbons adjacent (alpha) and nonadjacent to the ether functional group. Using the G4//B3LYP/6-311++G(2df,2pd) level of theory and the transition state theory, we estimated the rate constants and the Arrhenius coefficient for over 120 possible isomerization reactions. We examined the effect of ring size and ring atoms, revealing that 6- and 7-membered ring isomerizations were generally the fastest. The impact of the ether functional group on transition states was investigated by comparing reactions with identical ring size, peroxy, and radical positions, but with the ether functional group positioned either outside (i.e., out) or inside (i.e., in) the transition state ring, leading to differences in the rate constants. When comparing to analogous alkane rate constants, differences of up to an order of magnitude were observed, underscoring the need for caution when assigning rate rules by analogy. We applied our rate constants in the di-iso-butyl ether kinetic model and evaluated their influence on low-temperature chemistry finding that they altered the branching ratios by up to a factor of 9, highlighting the significance of site-specific rate constants for more accurate low-temperature modeling.

Accessing the Cloke-Wilson Rearrangement via Conjugate Addition of Phosphoranes to Michael Acceptors: A Route to Cyclopropanes and 5-Membered Ring Heterocycles Investigated by Density Functional and Ab Initio Theory.

Conjugate addition of unstabilized Wittig-type phosphonium ylides to 1,1-diacceptor- and 1-acceptor-substituted alkenes is investigated by density functional theory and high-level ab initio (DLPNO-CCSD(T)) calculations. The results indicate that the initial conjugate addition step should be facile with barriers predicted to be between 0 and 21 kcal mol-1. Potential intramolecular follow-up reactions include the formation of acceptor-substituted cyclopropanes as well as the formation of dihydrofuran derivatives via intramolecular SN2-type transition state structures. The barriers calculated for these potentially valuable cyclization reactions are substantial with Gibbs free energies of activation between 19 and 40 kcal mol-1. Competing reaction channels include Wittig olefination (for ketones and aldehydes), as well as Claisen condensation reactions. The reaction offers an alternative entry point to the nucleophile-catalyzed Cloke-Wilson rearrangement.

Characterization, stability, and skin application of astaxanthin particulates

PurposeAstaxanthin (AX), commonly used for dermal applications, exhibits anti-inflammatory and antioxidant activities; however, it has poor water solubility. In this study, we investigated the physicochemical properties of AX-containing particulates formulated using the amphiphilic graft copolymer Soluplus (polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer: Sol) and polyethylene glycol-2000 (PEG 2000); in addition, the stability and skin applications of AX particulates were investigated.MethodsAX, Sol, and PEG were mixed by weight to prepare AX particles using the hydration method. The prepared particles were subjected to stability evaluations including particle size distribution, zeta potential estimation, and fluorescence spectroscopy as well as physical evaluations including 1H-1H NOESY NMR spectral measurement, powder X-ray diffraction, and differential scanning calorimetry. Functional evaluations included singlet oxygen scavenging, skin permeation test, and fluorescence microscopy.ResultsRelatively stable particles of Sol/AX and Sol/PEG 2000/AX, approximately 100 nm and 125 nm in size, respectively, were formed at a mixed weight ratio (9/1) of 0.1 M Ascorbic Acid solution (0.1 M ASC) and a mixed weight ratio (8/1/1) of 0.1 M ASC, respectively, at 25 °C after storage for 14 days under light-shielded condition. Stability evaluations revealed a decrease in fluorescence intensity and color fading for Sol/AX = 9/1 and Sol/PEG 2000/AX = 8/1/1 (dispersion medium: distilled water); however, no change in fluorescence intensity of AX was observed immediately after preparation in Sol/AX = 9/1 and Sol/PEG 2000/AX = 8/1/1 (dispersion medium: 0.1 M ASC). The fluorescence intensity of AX did not fluctuate significantly immediately after adjustment, and the particles remained stable, showing a bright orange color with time. NMR spectra of Sol/AX = 9/1 and Sol/PEG 2000/AX (dispersion medium: 0.1 M ASC) showed the interactions between the CH3 group e from Sol (1.8 ~ 2.0 ppm) and the CH groups H-15,11 from AX (6.7 ~ 6.8 ppm), 8’,12’ (6.4 ~ 6.5 ppm), H-10,14 (6.4 ~ 6.5 ppm), and 7,7’ (6.2 ~ 6.3 ppm), indicating the disappearance of cross peaks. Furthermore, new cross peaks were identified for the CH3 group e of Sol (1.8 ~ 2.0 ppm), the 7-membered ring z of Sol (1.5 ~ 1.8 ppm), the 5-membered ring S of ASC (3.5 ~ 3.6 ppm), the CH group T (3.8 ~ 3.9 ppm), and the CH group U (4.7 ppm). Fluorescence microscopy observations of microparticles formulated with Sol/PEG 2000/AX showed a slight improvement in skin penetration.ConclusionNew AX particulates were formed using Sol/PEG 2000/AX = 8/1/1, suggesting that Sol/PEG 2000/AX maintained the stability and improved the skin penetration of AX.

Insights into the pore size distribution of amorphous silica membranes using gas permeation activation energies

Silica-based membranes exhibit significant promise for the separation of hydrogen from other larger gas molecules based on size sieving mechanism, particularly when employed in membrane reactors. Nevertheless, the migration of silanol bonds (Si–OH) formed under hydrothermal conditions leads to alterations in pore size, ultimately compromising the performance of the membrane. Therefore, this study focuses on determining the pore size of cobalt-doped silica membranes before and after hydrothermal treatment by the apparent activation energy of gas permeation. The Oscillator model and the effective medium theory are employed to estimate the potential pore size distribution, as well as to calculate the apparent activation energy and permeability. The calculated apparent activation energy is compared with experimental data to identify the most probable pore size distribution, which showed the minimum activation energy error to the experimental value. The calculated permeability based on the identified pore size distribution is in line with experimental permeability, which validated the identified pore size distribution. Since silica-based membrane is generally applied in hydrothermal conditions, our model successfully identifies the changes in pore size of silica-based membranes after hydrothermal treatment. The results demonstrated that hydrothermal treatment significantly impacts the pore size of silica-based membranes. Specifically, 5-membered rings are prevalent in the intact membrane, but after hydrothermal treatment, there is a gradual shift of the pore size distribution towards larger pores, potentially leading to a decrease in sieving performance. This methodology presents a promising approach for determining intriguing pore size information of porous materials.

Gold(III)-Induced Amide Bond Cleavage In Vivo: A Dual Release Strategy via π-Acid Mediated Allyl Substitution.

Selective cleavage of amide bonds holds prominent significance by facilitating precise manipulation of biomolecules, with implications spanning from basic research to therapeutic interventions. However, achieving selective cleavage of amide bonds via mild synthetic chemistry routes poses a critical challenge. Here, we report a novel amide bond-cleavage reaction triggered by Na[AuCl4] in mild aqueous conditions, where a crucial cyclization step leads to the formation of a 5-membered ring intermediate that rapidly hydrolyses to release the free amine in high yields. Notably, the reaction exhibits remarkable site-specificity to cleave peptide bonds at the C-terminus of allyl-glycine. The strategic introduction of a leaving group at the allyl position facilitated a dual-release approach through π-acid catalyzed substitution. This reaction was employed for the targeted release of the cytotoxic drug monomethyl auristatin E in combination with an antibody-drug conjugate in cancer cells. Finally, Au-mediated prodrug activation was shown in a colorectal zebrafish xenograft model, leading to a significant increase in apoptosis and tumor shrinkage. Our findings reveal a novel metal-based cleavable reaction expanding the utility of Au complexes beyond catalysis to encompass bond-cleavage reactions for cancer therapy.

Enantioselective Nickel-Catalyzed α-Spirocyclization of Lactones.

Herein we report a strategy for the enantioselective synthesis of spirocycles containing all-carbon quaternary centers via nickel-catalyzed intramolecular addition of lactone enolates to aryl nitriles. The established lactone α-spirocyclization efficiently and enantioselectively forges 5-, 6-, and 7-membered rings, performing best in the synthesis of 7-membered rings (up to 90% ee). This discovery represents an expansion of the synthetic toolkit for enantioselective spirocyclization, providing access to chiral, pharmaceutically relevant spirocyclic products.

Synthesis, Characterization, and Application of Amorphous Silica-Aluminas Support for Fischer-Tropsch Wax Hydrocracking Catalysts.

High-performance amorphous silica-aluminas (ASAs) were prepared prior to the formation of the 10-membered ring (10-MR) ZSM-5 zeolite by regulating the hydrothermal processing time. Their structures, morphologies, acidity properties, and Si-Al coordination were well studied. Particularly, a facile FTIR method of in-situ adsorbing bulky 2,6-dimethlypyridine followed by pyridine adsorption was innovatively utilized to quantify the Brønsted acid sites in micropores. All the ASAs samples were transformed into catalysts by loading with 0.5 wt % Pt. The structure-activity relationship, especially from the strength, density, and location of Brønsted acid sites, was investigated by Fischer-Tropsch synthesis (FTS) wax hydrocracking. The evaluation results showed that the medium strong Brønsted acid sites located on the external surface played a crucial role in the activity. Contrary to the general belief that larger pores favor the production of heavy cracking fractions, the ASAs with a 10-MR microporous structure proved to be more effective for diesel production than those with a 12-membered ring (12-MR). Strong Brønsted acid sites in micropores were less conducive to diesel production mainly due to stronger adsorption at these sites and steric hindrance from the microporous system. Furthermore, the Pt/AS-20 catalyst with few intramicropore Brønsted acid sites exhibited high diesel selectivity (83.3%) at 50.5% conversion under industrially relevant reaction conditions, which provides a significant opportunity to develop FTS wax hydrocracking catalysts more rationally.

Self-Assembly of Model Three- and Four-Patch Colloidal Particles in Two Dimensions.

A coarse-grained effective solvent model of two-patch particles is extended to study the self-assembly of three- and four-patch particles to two-dimensional honeycomb and square lattices, respectively. Employing this model, grand canonical ensemble simulations are done to calculate vapor-liquid equilibria and the critical temperatures for patchy particles of various patch widths. The range of stability of the liquid, although very limited compared to isotropic particles, which interact through a longer-range potential, depends on the patch width and on the number of patches. Biased sampling and unbiased simulations are also done to investigate the mechanism of nucleation and crystal growth for honeycomb and square lattices, self-assembled from three- and four-patch particles, respectively. A two-step mechanism governs the nucleation of both lattices. In the first step, the particles form a dense amorphous network, and in the second step, the particles inside the amorphous network reorient to form crystalline nuclei. Barrier heights for the nucleation of honeycomb and square lattices are 7.8 kBT and 7.4 kBT, which are close to the reported values for the nucleation of the kagome lattice. In agreement with confocal microscopy experiments, the self-assembly in a honeycomb lattice involves the formation of 5- to 7-membered rings. The 5- and 7-membered rings hamper the nucleation of the honeycomb lattice, through defect formation and rotation of the symmetry planes of crystals that form at their surfaces. With the progress of self-assembly, a substantial amount of restructuring of the defects and crystals in their vicinity is needed to heal the defects.

(Invited) Electrochemistry of the 1,1,N,N-Tetramethyl[N](2,11)Teropyrenophanes

Polycyclic aromatic hydrocarbons (PAH) have been of broad interest for many decades. This is due largely to their extended π systems, which imbue them with optical and electronic properties that can be exploited in a variety of organic electronic devices. A current trend in PAH chemistry is the construction of ever-larger and more elaborate aromatic systems. A major challenge associated with this work is to maintain solubility. For innately planar PAH, the standard tactic is to append multiple solubilizing groups to the periphery of the aromatic system. The drawbacks to this are that 1) the mass of solubilizing groups can outweigh that of the PAH, 2) the presence of the solubilizing groups severely limits or rules out doing chemistry on the periphery and 3) the tactic becomes less and less effective as the size of the PAH becomes very large. An alternative and very effective way to boost solubility is to bring about nonplanarity in a PAH. This can be achieved through the presence of nonbonded interactions (as in helicenes), the presence of non-6-membered rings (as in corannulene) and by bridging the aromatic system (i.e. incorporating it into a cyclophane).Cyclophanes constitute a very large and diverse class of compounds. The simplest cyclophanes (the [n]cyclophanes) consist of just one aromatic system and one aliphatic bridge. These cyclophanes are especially interesting because the structure of the aromatic system can be changed by varying the length of the bridge. This enables the study of how the chemical and physical properties of a particular PAH are affected by incremental changes in structure without any complications arising from intramolecular π-π interactions or changes in the character or position of the substituents (the bridge). Understanding the relationships between structure and properties can underpin efforts to tailor properties of organic compounds for use as materials in devices. Very few [n]cyclophanes that have a large PAH are known, so there is plenty of room for exploration in this area.The PAH of interest in this work is teropyrene. It is a member of the ropyrene series of aromatic compounds, which evolve into armchair-edged graphene nanoribbons (GNR) as they propagate. Teropyrene has 10 6-membered rings, 36 carbon atoms and vanishingly low solubility. Only a handful of teropyrene derivatives are known. We have developed a synthetic route to a series of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n = 7-10), which feature a teropyrene system with an end-to-end bend ranging from 145° (n = 10) to 178° (n = 7) and have very good solubility in a variety of organic solvents. Details of the redox behaviour of these teropyrenophanes will be presented. Figure 1

(Invited) Molecular Donor-Acceptor Systems Derived from Aromatic Heterocycle-Fused Porphyrins

Photoinduced charge separation (CS) in molecular donor-acceptor (D-A) systems is crucial for achieving efficient solar energy conversion in various applications. Despite significant efforts to develop molecular D-A systems over the past decades, it remains a challenge to bring the lifetime of the charge separation state to ms range, which is much shorter than the CS lifetime (~1 s) in natural photosynthetic systems. In this talk, a donor-acceptor system with long-lived charge-separation state (37.2 μs) will be presented. This donor-acceptor system was derived from π-extended porphyrins fused with aromatic heterocycles. Porphyrins fused with aromatic heterocycles represent one fascinating yet very challenging frontiers in chemistry and materials science.1-4 The Wang group has been engaged in developing concise and versatile synthetic and functionalization methods for π-extended porphyrins. The availability of these methods offers easy access to many π-extended porphyrins with novel functionalities.5-7 In this talk, the synthesis, characterization, and the optical and photophysical properties of π-extended porphyrins fused with 5-, 6, and 7-membered rings including 12H-benzo[f]benzo[4,5]imidazo[2,1-a]isoindole and 1,10-phenanthroline, porphyrins will also be presented. Reference Stepien, E. Gonka, M. Zyla and N. Sprutta, Chem. Rev., 2017, 117, 3479-3716.Narita, X. Y. Wang, X. Feng and K. Mullen, Chem. Soc. Rev., 2015, 44, 6616-6643.P. Lewtak and D. T. Gryko, Chem. Commun., 2012, 48, 10069-10086.K. S. Davis, A. L. Thompson and H. L. Anderson, J. Am. Chem. Soc., 2011, 133, 30-3.Hu, M. B. Thomas, W. A. Webre, A. Moss, R. G. W. Jinadasa, V. N. Nesterov, F. D’Souza and H. Wang, Angew. Chem. Int. Ed., 2020, 45 (132), 20250-20257.Moss, Y. Jang, J. Arvidson, V. N. Nesterov, F. D’Souza and H. Wang, Chem. Sci., 2022, 13, 9880 -9890.Moss, D. E. Nevonen, Y. Hu, V. N. Nesterov, V. Nemykin and H. Wang*, ACS Phys. Chem. Au, 2022, 2, 6, 468-481.

Low-silica zeolite MTT: Synthesis and efficient catalysis in methanol dehydration

Zeolite MTT features a one-dimensional (1D) 10-membered ring (10 MR) straight channel system. This unique structure provides superior catalytic performance in petrochemical processes such as isomerization, dewaxing, and olefin oligomerization. The conventional synthesis of zeolite MTT typically requires large amounts of organic structure directing agents (OSDA), and the resulting zeolite MTT usually has a Si/Al ratio greater than 20. Herein, we present a facile strategy for synthesizing zeolite MTT possessing a low Si/Al ratio of 12.5 and a greatly improved specific surface area of 308.0 m2/g with the assistance of MTT seeds. This low-silica zeolite MTT demonstrates a higher methanol conversion (84 %) at a low temperature (170 °C) in the methanol dehydration reaction compared to conventionally synthesized zeolite MTT, which achieves less than 70 % conversion.

Rapid Access to Divergent Fused Polycycles Via One-Pot A3 Coupling and Intramolecular Diels-Alder Reaction.

Divergent nitrogen-containing fused polycyclic ring systems are constructed from simple starting materials via a one-pot aldehyde-alkyne-amine (A3) coupling and intramolecular Diels-Alder reaction. This domino reaction directly furnishes linear 5/5/5 and 5/5/6, or nonlinear 5/5/6/5, polycyclic rings containing an oxa-bridged fused 5/5 bicycle and a 1,6-enyne substructure. One-step derivation of the oxa-bridged 5/5 bicycle leads to a polyfunctionalized 5/5 bicycle with tetrahydrofuran fused back-to-back to pyrroline or a 6/5 bicycle with the hexahydro-1H-isoindole structure, while cycloisomerizing the enyne substructure adds an extra fused 5-membered ring to afford functionalized linear 5/5/5/5 or 5/5/5/5/5 fused ring systems from selected substrates. In addition, the one-pot product can be designed so that the alkyne moiety is hydroalkoxylated to form an additional heterocyle in a linear 5/5/5/6 or nonlinear 5/5/6/5/5 ring system. This diversity-oriented synthetic approach thus allows rapid access to an under-explored structural space for discovery of new biological or non-biological activities or functions.

Influence of the Bis-Carbene Ligand on Manganese Catalysts for CO2 Electroreduction.

First row transition metal complexes have attracted attention as abundant and affordable electrocatalysts for CO2 reduction. Manganese complexes bearing bis-N-heterocyclic carbene ligands defining 6-membered ring metallacycles have proven to reduce CO2 to CO selectively at very high rates. Herein, we report the synthesis of manganese carbonyl complexes supported by a rigid ortho-phenylene bridged bis-N-heterocyclic carbene ligand (ortho-phenylene-bis(N-methylimidazol-2-ylidene), Ph-bis-mim), which defines a 7-membered ring metallacycle. We performed a comparative study with the analogues complexes bearing an ethylene-bis(N-methylimidazol-2-ylidene) ligand (C2H4-bis-mim) and a methylene-bis(N-methylimidazol-2-ylidene) ligand (CH2-bis-mim), and found that catalysts comprising a seven-membered metallacycle retain similar selectivity and activity as those with six-membered metallacycles, while reducing the overpotential by 120-190 mV. Our findings reveal general design principles for manganese bis-N-heterocyclic carbene electrocatalysts, which can guide further designs of affordable, fast and low overpotential catalysts for CO2 electroreduction.