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Positively charged aromatic and aliphatic quaternary ammonium groups were successfully installed in metal–organic frameworks (MOFs) through post-synthetic modification (PSM) and post-synthetic exchange (PSE) for hydroxide conductivity studies.

A photodegradable nitrophenylene polymer was preparedviaring-opening metathesis polymerization (ROMP). The resulting polymer was degraded in the presence of UVA light without any chemical additives within 1 hour.

Novel post-synthetic ligand cyclization (PSLC) strategy for metal–organic frameworks (MOFs) bearing regioisomeric functional groups has been developed to install benzo-fused heterocycles in MOFs.

Poly(p-phenylenevinylene)s (PPVs), a staple of the conductive polymer family, consist of alternating alkene and phenyl groups in conjugation. The physical properties of this organic material are intimately linked to the cis/trans configuration of the alkene groups. While many synthetic methods afford PPVs with all-trans stereochemistry, very few deliver the all-cis congeners. We report herein a synthesis of all-cis PPVs with living characteristics via stereoretentive ring-opening metathesis polymerization (ROMP). Exquisite catalyst control allows for the preparation of homopolymers or diblock copolymers with perfect stereoselectivity, narrow dispersities, and predictable average molar masses. All-cis PPVs can then serve as light-responsive polymers through clean photoisomerization of the stilbenoid units.

The expanding scope of chemical reactions applied to nucleic acids has diversified the design of nucleic acid-based technologies that are essential to medicinal chemistry and chemical biology. Among chemical reactions, visible light photochemical reaction is considered a promising tool that can be used for the manipulations of nucleic acids owing to its advantages, such as mild reaction conditions and ease of the reaction process. Of late, inspired by the development of visible light-absorbing molecules and photocatalysts, visible light-driven photochemical reactions have been used to conduct various molecular manipulations, such as the cleavage or ligation of nucleic acids and other molecules as well as the synthesis of functional molecules. In this review, we describe the recent developments (from 2010) in visible light photochemical reactions involving nucleic acids and their applications in the design of nucleic acid-based technologies including DNA photocleaving, DNA photoligation, nucleic acid sensors, the release of functional molecules, and DNA-encoded libraries.

As hydrogen-bond donors and acceptors, N,N′-disubstituted sulfamides have been used in a range of applications from medicinal chemistry to anion-binding catalysis. However, compared to ureas or thioureas, the utilization of this unique moiety remains marginal, in part because of a lack of general synthetic methods to access unsymmetrical sulfamides. Specifically, polysulfamides are a virtually unknown type of polymer despite their potential utility in non-covalent dynamic networks, an intense area of research in materials science. We report herein a practical and efficient process to prepare unsymmetrical sulfamides via Sulfur(vi)-Fluoride Exchange (SuFEx) click chemistry. This process was then applied to synthesize polysulfamides. Thermal analysis showed that this family of polymers possess high thermal stability and tunable glass transition temperatures. Finally, hydrolysis studies indicated that aromatic polysulfamides could be recycled back to their constituting monomers at the end of their life cycle., A general, practical, and efficient synthesis of N,N′-disubstituted sulfamides has been developed and applied to the preparation of polysulfamides, a virtually unknown class of polymers.

Poly(p-phenylene vinylene)s (PPVs), a staple of the conductive polymer family, consist of alternating alkene and phenyl groups in conjugation. The physical properties of this organic material are intimately linked to the cis/trans configuration of the alkene groups. While many synthetic methods afford PPVs with alltrans stereochemistry, very few deliver the all-cis congeners. We report herein the first synthesis of all-cis PPVs with living characteristics via stereoretentive ring-opening metathesis polymerization (ROMP). Exquisite catalyst control allows for the preparation of homopolymers or diblock copolymers with perfect stereoselectivity, narrow dispersities, and predictable molecular weights. All-cis PPVs can then serve as light-responsive polymers through clean photoisomerization of the stilbenoid units.

A glucose-based bioadhesive, poly(2-methacrylamido glucopyranose-co-N-methacryloyl-3,4-dihydroxyl-L-phenylalanine-co-8-azidooctyl methacrylate) [poly(MG-co-MDOPA-co-AOM)], has been synthesized by thermally-initiated free radical polymerization. The new bioadhesive is composed of three modules: a hydrophilic glycopolymer segment, a mussel-inspired catechol segment, and a crosslinking azide segment. Poly(ethylene glycol) (PEG)-based crosslinker, (1R,8S,9s)-bicyclo[6.1.0]non-4-yn-9-ylmethyl PEG (BCN-PEG) was synthesized separately. Bulk adhesion properties of the terpolymer were enhanced by covalent bond forming crosslinking via strain-promoted azide–alkyne cycloaddition (SPAAC). The occurrence of SPAAC was confirmed by 1H NMR and FT-IR. After moistening the adhesive and the crosslinker, BCN-PEG with water, adhesion properties were examined by a lap shear strength test on porcine skins. The control of adhesion was studied under various crosslinker concentrations, crosslinking durations, and crosslinker lengths. Even without crosslinking, the new terpolymer adhesive demonstrated 20-fold higher adhesion strength (115 kPa) compared to a commercial rubber cement (5.8 kPa). The most significant factor to control for adhesion was crosslinker length. BCN-PEG was prepared with 134 and 43 repeating units of PEG. Crosslinking with the long crosslinker, BCN-PEG (PEG repeating units: 134), did not enhance adhesion strength meaningfully. However, crosslinking the short crosslinker BCN-PEG (repeating units: 43) showed significant improvement in work of adhesion (150% higher than uncrosslinked). The overall revealed features of strong adhesion on biological surfaces, structural similarity to natural carbohydrate, water compatibility, controllability of adhesion strength, and non-toxic adhesion enhancement principle via SPAAC crosslinking, suggest that the new glucose-based bioadhesive can be successfully used for biomedical applications.

Silver carbonate (Ag2CO3), a common transition metal-based inorganic carbonate, is widely utilized in palladium-catalyzed C–H activations as an oxidant in the redox cycle. Silver carbonate can also act as an external base in the reaction medium, especially in organic solvents with acidic protons. Its superior alkynophilicity and basicity make silver carbonate an ideal catalyst for organic reactions with alkynes, carboxylic acids, and related compounds. This review describes recent reports of silver carbonate-catalyzed and silver carbonate-mediated organic transformations, including cyclizations, cross-couplings, and decarboxylations.

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst removal via host-guest interactions. The new NHC ligand possesses an adamantyl (guest) tethered linear ethylene glycol units for hydrophobic inclusion into the cavity of a β-cyclodextrin (β-CD) host compound. The new NHC ligand was applied to a Ru-based olefin metathesis catalyst. The Ru catalyst demonstrated excellent activity in representative ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions in aqueous media as well as organic solvent, CH(2)Cl(2). After the reaction was complete, the lingering Ru residue was removed from the aqueous solution with the efficiency of more than 99% (53 ppm of Ru residue) by simple filtration utilizing a host-guest interaction between insoluble silica-grafted β-CD (host) and the adamantyl moiety (guest) on the catalyst. The new Ru catalyst also demonstrated high removal efficiency via extraction when the reaction is run in organic solvent by partitioning the crude reaction mixture between layers of diethyl ether and water. In this way, the catalyst stays in aqueous layer only. In organic layer, the residual Ru amount was only 0.14 ppm in the RCM reactions of diallyl compounds.

A study of reaction kinetics and removal efficiency of a family of ruthenium (Ru)-based olefin metathesis catalysts containing ethylene-glycol-oligomer-tethered N-heterocyclic carbene (NHC) ligands has been carried out, with a focus on variation of ethylene glycol oligomer length. The length of ethylene glycol oligomer was precisely defined by sequential addition of repeating units. Due to the dual solubility of ethylene glycol oligomer, the produced catalyst was highly soluble in both aqueous and organic solvents (dichloromethane). In aqueous solution, the polarity increase with longer ethylene glycol oligomers enhanced the reactivity in homogeneous solution. The length of ethylene glycol oligomer did not significantly affect olefin metathesis rate in organic solution. Yet the removal efficiency of catalyst strongly relies on the length of ethylene glycol oligomer. A longer ethylene glycol oligomer demonstrated better catalyst removal efficiency. The tested catalyst removal method was aqueous extraction from organic solution using its higher water solubility property compared to its lower organic solvent (dichloromethane) solubility property. The results obtained from the aqueous extraction catalyst removal method demonstrated similar and/or better removal rates compared to previously reported host-guest catalyst removal methods.

A highly removable N-heterocyclic carbene ligand for a transition-metal catalyst in aqueous media via host–guest interactions has been developed. Water-soluble adamantyl tethered ethylene glycol in the ligand leads a hydrophobic inclusion into the cavity of β-cyclodextrin. Ruthenium (Ru) olefin metathesis catalyst with this ligand demonstrated excellent performance in various metathesis reactions in water as well as in CH2Cl2, and removal of residual Ru was performed via filtration utilizing a host–guest interaction and extraction.

The first gold-catalyzed intermolecular coupling of alkynoates and allylic ethers is presented.

The first gold-catalyzed intermolecular coupling of alkynoates and allylic ethers invoking alkoxy addition and [3,3]-sigmatropic rearrangement as the key mechanism has been developed. Remarkably, the reaction showed complete chemoselectivity toward the pathway initiated by the alkoxy addition to alkynes. This unprecedented reactivity led to a new access to diversely substituted β-alkoxyacrylates in a highly efficient manner.

Cycloisomerization of N,S- or N,O-acetals [(I) or (III), resp.] leads to piperidinones (II), whereas compound (IV) having an additional alkyl group at the propargylic position yields thioether (V).

A new gold(I)-catalyzed cycloisomerization to access highly substituted piperidines has been developed. By combining a conceptually new way of generating iminium ions using cationic gold(I) complexes and an efficient cyclization reaction that can minimize a potentially competing aza-Cope rearrangement, the proposed reaction successfully circumvents a long-standing problem in the classical aza-Prins reaction. Synthetic utility of the catalytic reaction was demonstrated by a synthesis of optically active 2-alkyl-piperidin-4-one.

Piperidine is one of the most common building blocks of alkaloids. For this reason, there have been great efforts to develop new synthetic methods for piperidine structures. Recently, we developed a unique approach to highly substituted piperidin-4-ones, using gold(I)-catalyzed cycloisomerization of mixed N,O-acetals derived from homopropargylic amines. In progress of applying this method to total synthesis of natural alkaloids, special attention was given to the bicyclic indolizidine and quinolizidine structures, which are frequently found in various bioactive alkaloids. For examples, swainsonine and homopumiliotoxin 223G are well known natural products that contain either indolizidine or quinolizidine core structures. As a consequence, we anticipated that the development of general synthetic routes for the construction of these core structures would assist the total synthesis of natural products bearing azabicyclic systems. As illustrated in Scheme 1, we expected that the indolizidine (n = 1) and quinolizidine (n = 2) bicyclic framework 1 could be easily synthesized from the cyclic enol ether 2, which could be accessed by the gold(I)-catalyzed cycloisomerization of mixed N,O-acetal precursor 3. We intended to prepare the precursor 3 from readily available 4. As depicted in Scheme 2, our initial efforts focused on the preparation of mixed N,O-acetal substrate 8 for the gold(I)catalyzed cycloisomerization. Epoxidation of PMB ether 5 with m-CPBA followed by the addition of TMS-acetylide and the subsequent desilylation generated homopropargylic alcohol 6 in 36~45% yield over three steps. Transformation of this compound into the homopropargylic amine 7 went uneventfully using a three-step sequence shown in Scheme 2. Preparation of the key substrate 8 was accomplished by the Cbz protection of the amino group followed by the introduc

1 10 AgSbF6 (10) rt 20 h 40% 2 10 AgBF4 (10) rt 22 h 40% 3 10 AgOTf (10) rt 4 h 55% 4 10 AgOTf (10) 0 C 10 h 81% isolated yield after two-step conversion. 1d was isolated in 15% yield. 1d was isolated in 7% yield. Developing new methodologies for the synthesis of piperidines have been attracting the interest of synthetic chemists. Recently, we reported gold(I)-catalyzed cycloisomerization of N,O-mixed acetals generated from homopropargylic amines, which led to a unique approach to highly substitutued piperidin-4-ones. A key aspect of this reaction is the chemoselective activation of alkynes (path A) over the activation of ether groups (path B), as shown in Scheme 1. In an effort to extend the scope of this reaction, we envisioned gold(I)-catalyzed cycloisomerization of the corresponding N,S-mixed acetals. Because the thioether groups are known to attack alkynes in the presence of gold catalysts, the main goal of this study was to compare the reactivity between N,O-acetals and N,S-acetals for the cycloisomerization reaction. Moreover, the cycloisomerization of mixed N,S-acetal would be highly efficient for the preparation of 2-alkylpiperidine alkaloids including coniine and coniceine, because the thioether moiety can be easily removed with the concomitant hydrogenation of the olefin in single step. At the outset of the study, we expected that the cycloisomerization reaction of the N,S-acetals should be faster than N,O-acetal, based on the relative nucleophilicity. However, a preliminary study using 5 mol % of Au[P(C6F5)3]SbF6 showed only poor conversion. Increasing the catalyst loading to 10 mol % provided a mixture of the cycloisomerization product 1b and the piperidin-4-one 1c in ~45% combined yield, although the starting material was completely consumed. Our extensive efforts to isolate the cycloisomerization product in good yields were fruitless, due to the extensive hydration of 1b to form ketone 1c. Thus, we sought to obtain the ketone 1c by treating the crude mixture generated from the cycloisomerization reaction with catalytic p-TsOH (20 mol %). Under this two-step protocol, the ketone 1c was obtained in 40% yield (entry 1, Table 1). Then, we explored the effect of various counteranions. Although using AgBF4 had no effect (entry 2), changing to AgOTf increased the yield to 55% (entry 3).

A new gold(I)-catalyzed cycloisomerization to access highly substituted piperidines has been developed. By combining a conceptually new way of generating iminium ions using cationic gold(I) complexes and an efficient cyclization reaction that can minimize a potentially competing aza-Cope rearrangement, the proposed reaction successfully circumvents a long-standing problem in the classical aza-Prins reaction. Synthetic utility of the catalytic reaction was demonstrated by a synthesis of optically active 2-alkyl-piperidin-4-one.