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The Grubbs G-I or G-II catalyst gives the ruthenium ethoxy carbene complex, which catalyzes ring-opening cross metathesis (ROCM) of a strained cyclic alkene to give a diene where one of the two alkene moieties in the product contains an ethoxy substituent. No polymeric products are detected. Hydrocarbons such as parent norbornene or substituted cyclopropenes can proceed with the reaction smoothly. Tertiary amines, N-alkylimides, esters, and aryl or alkyl bromides remain intact under the reaction conditions. In addition to vinyl ethers, vinylic esters can also be used. The time required to reach a 50% yield of the ROCM product t50 varies from 0.01 to 140 h depending on the strain and nucleophilicity of the double bond. Anchimeric participation of an electron-rich group would result in significant enhancement of the reactivity, and the t50 could be as short as several minutes. A similar substrate without such a neighboring group shows a much slower rate. An exo-norborne derivative reacts much faster than the corresponding endo-isomer. Alkenes with poor nucleophilicity are less favored for the ROCM process, so is less strained cyclooctene.

Lewis acids increase the catalytic activity of classical heterogeneous catalysts and molecular d0 tungsten oxo alkylidenes in a variety of olefin metathesis processes. The formation of labile adducts between the metal complex and the Lewis acid has been observed experimentally and suggested to be involved in the catalyst activity increase. In this contribution, DFT (M06) calculations have been performed to determine the role of Lewis acids on catalyst activity, Z-/E- selectivity and stability by comparing three W(E)(CHR)(2,5-dimethylpyrrolide)(O-2,6-dimesithylphenoxide) (E = oxo, imido or oxo-Lewis acid adduct) alkylidenes. Results show that the formation of the alkylidene—Lewis acid adducts influences the reactivity of tungsten oxo alkylidenes due to both steric and electronic effects. The addition of the Lewis acid on the E group increases its bulkiness and this decreases catalyst Z-selectivity. Moreover, the interaction between the oxo ligand and the Lewis acid decreases the donating ability of the former toward the metal. This is important when the oxo group has either a ligand in trans or in the same plane that is competing for the same metal d orbitals. Therefore, the weakening of oxo donating ability facilitates the cycloaddition and cycloreversion steps and it stabilizes the productive trigonal bipyramid metallacyclobutane isomer. The two factors increase the catalytic activity of the complex. The electron donating tuneability by the coordination of the Lewis acid also applies to catalyst deactivation and particularly the key β-hydride elimination step. In this process, the transition states show a ligand in pseudo trans to the oxo. Therefore, the presence of the Lewis acid decreases the Gibbs energy barrier significantly. Overall, the optimization of the E group donating ability in each step of the reaction makes tungsten oxo alkylidenes more reactive and this applies both for the catalytic activity and catalyst deactivation.

Norbornene derivatives (NBEs) are common monomers for living ring-opening metathesis polymerization and yield polymers with low dispersities and diverse functionalities. However, the all-carbon backbone of poly-NBEs is non-degradable. Here we report a method to synthesize degradable polymers by copolymerizing 2,3-dihydrofuran with NBEs. 2,3-Dihydrofuran rapidly reacts with Grubbs catalyst to form a thermodynamically stable Ru Fischer carbene-the only detectable active Ru species during copolymerization-and the addition of NBEs becomes rate determining. This reactivity attenuates the NBE homoaddition and allows uniform incorporation of acid-degradable enol ether linkages throughout the copolymers, which enables complete polymer degradation while maintaining the favourable characteristics of living ring-opening metathesis polymerization. Copolymerization of 2,3-dihydrofuran with NBEs gives low dispersity polymers with tunable solubility, glass transition temperature and mechanical properties. These polymers can be fully degraded into small molecule or oligomeric species under mildly acidic conditions. This method can be readily adapted to traditional ring-opening metathesis polymerization of widely used NBEs to synthesize easily degradable polymers with tunable properties for various applications and for environmental sustainability.

Materials capable of degradation upon exposure to light hold promise in a diverse range of applications including biomedical devices and smart coatings. Despite the rapid access to macromolecules with diverse compositions and architectures enabled by ring-opening metathesis polymerization (ROMP), a general strategy to introduce facile photodegradability into these polymers is lacking. Here, we report copolymers synthesized via ROMP that can be degraded by cleaving the backbone in both solution and solid states under irradiation with a 52 W, 390 nm Kessil LED to generate heterotelechelic low-molecular-weight fragments. To the best of our knowledge, this work represents the first instance of the incorporation of acylsilanes into a polymer backbone. Mechanistic investigation of the degradation process supports the intermediacy of an α-siloxy carbene, formed via a 1,2-photo Brook rearrangement, which undergoes insertion into water followed by cleavage of the resulting hemiacetal.

The ruthenium-catalyzed cross-metathesis of alkenes and alkynes, which splits the alkene C═C double bond and couples one-half to each carbon of the alkyne C≡C triple bond, is one of the most efficient tools for the synthesis of 1,3-dienes, with wide-ranging applications, including pharmaceutical and polymer chemistry. In contrast, inorganic main-group metathesis reactions are restricted to a handful of examples of heavier p-block multiple bonds (P═P, Ge═Ge, and E≡E, E = Ge, Sn, Pb). We now report the first examples of thermally induced, transition-metal-free cross-metathesis between an organic alkyne and inorganic cyclic alkyl(amino)carbene (CAAC)-stabilized B═B double bonds, which yield fully planar, π-delocalized 1,8-diaza-3,6-diboraoctatetraenes. Density functional theory studies show that these compounds have an open-shell singlet biradical ground state with a thermally accessible closed-shell state. In-depth computational mechanistic analyses show that they are formed via a biradical cycloaddition-cycloreversion mechanism. Finally, unlike their organic counterparts, these B,N-analogues of octatetraene can undergo two-electron chemical reduction to form diamagnetic dianions.

Novel functionalized azaheterocycles with multiple chiral centers have been accessed from readily available norbornene β-amino acids or β-lactams across a stereocontrolled synthetic route, based on ring-opening metathesis (ROM) of the staring unsaturated bicyclic amino esters, followed by selective cyclization through ring-closing metathesis (RCM). The RCM transformations have been studied under various experimental conditions to assess the scope of conversion, catalyst, yield, and substrate influence. The structure of the starting norbornene β-amino acids predetermined the structure of the new azaheterocycles, and the developed synthetic route took place with the conservation of the configuration of the chiral centers.

An oxocarbenium-olefin cross metathesis occurs during Bronsted acid catalyzed reactions of 1H-isochromene acetals with vinyl diazo compounds. Formally a carbonyl-alkene [2 + 2]-cyclization between isobenzopyrylium ions and the vinyl group of vinyl diazoesters, the retro-[2 + 2] cycloaddition produces a tethered alkene and a vinyl diazonium ion that, upon loss of dinitrogen, undergoes a highly selective carbocationic cascade rearrangements to diverse products whose formation is controlled by reactant substituents. Polysubstituted benzobicyclo[3.3.1]oxocines, benzobicyclo[3.2.2]oxepines, benzobicyclopropane, and naphthalenes are obtained in good to excellent yields and selectivities. Furthermore, isotopic tracer and control experiments shed light on the oxocarbenium-olefin metathesis/rearrangement process as well as on the origin of the interesting substituent-dependent selectivity.

A systematic investigation of the polymerization of representative diphenylacetylenes with TaCl5 and cocatalysts suggested that low-valent Ta species, which are formed by in situ reduction of TaCl5 by the cocatalysts, are involved in the polymerization and that the polymerization reaction proceeds by an insertion ring expansion mechanism via the formation of tantalacyclopentadiene intermediates, rather than the previously considered metathesis mechanism. This polymerization mechanism indicates the production of unprecedented cis-stereoregular cyclic poly(diphenylacetylene)s. Indeed, the possibilities of a cyclic structure and high cis-stereoregularity of the resulting polymers were reasonably supported by the results of their detailed atomic force microscopy (AFM) and NMR analyses, respectively.

Branched polymers have found utility in an array of fields due to the high density of functional groups combined with unique physical properties. Despite the abundant methods reported to synthesize various branched structures, controlling parameters such as the location of branch points and molecular weight distribution still remains a challenge. This report explores the ability of enyne-containing branching agents to synthesize star and miktoarm star polymers through a convergent synthesis pathway using ring-opening metathesis polymerization (ROMP). The branching agents contain an enyne metathesis terminator covalently linked to a norbornene monomer. When these agents are introduced into a living ROMP, macromonomers are generated in situ that continue to propagate via a grafting-through process with the remaining living chains. This strategy permits control over the degree of polymerization of the star arms, control of the number of star arms, and chain-extension with additional monomer to produce functional asymmetric miktoarm star polymers.

We report the first total synthesis of shagenes A and B, which are tricyclic terpenoids containing a cis-substituted cyclopropane, via ring-closing metathesis of an enamide and Ir-catalyzed double-bond isomerization of an alkylidenecyclopropane. Chemo- and diastereoselectivity in the distorted cis-substituted structures were controlled by the alkylidenecyclopropane reactivity and using the ketone functionality as a remote directing group for the Ir catalyst, respectively. The total synthesis suggested the absolute configuration of shagenes., Shagene AおよびBの化学合成 --リーシュマニア症の治療薬リードの創製を目指して--. 京都大学プレスリリース. 2021-09-10.

The reaction of 1,3,5,7-cyclooctatetraene with silicon-substituted ethylenes has been studied for the first time. It is shown that vinyltrimethylsilane is inactive in the reaction, and vinyltrichlorosilane forms 7-trichlorosilyltricyclo[4.2.2.02,5]deca-3,9-diene in up to 12% yield. A new silicon-substituted monomer 7‑trimethylsilyltricyclo[4.2.2.02,5]deca-3,9-diene containing 92% of the endo-isomer has been synthesized by methylation of the chloroadduct. The metathesis polymerization of the final monomer mediated by the Grubbs Ru catalysts of the first and second generations is studied. A new poly(7-trimethylsilyltricyclo[4.2.2.02,5]deca-3,9-diene) containing a bulky bicyclic fragment and predominantly trans-double bonds in the main chain (up to 94%) is obtained in 90–96% yields. The polymer is characterized by the highest glass transition point (187°C) in the series of monotrimethylsilyl-substituted polynorbornenes. The double bonds present in the monomer unit open up prospects for further modification.

The metathesis of carbon–carbon double bonds—the ‘reshuffling’ of their constituting carbene fragments—is a tremendously important preparative tool in industry and academia. Metathesis of heavier alkene homologues is restricted to occasional unproductive examples in phosphorus chemistry and cross-metathesis to mixed heavier alkynes. We now report the thermally induced, transition-metal-free metathesis of purpose-built unsymmetrically substituted digermenes. The A2Ge=GeAB starting materials are thus converted to symmetrically substituted derivatives of the A2Ge=GeA2 and ABGe=GeAB types. The use of tethered auxiliary donors (dimethylaniline groups) in substituents B ensures intramolecular donor–acceptor stabilization of the transient germylene fragments, the intermediacy of which is proven by trapping experiments. Density functional theory calculations shed light on the thermodynamic driving force of the metathesis and validate the crucial role of the tethered donor. With an analogously equipped bridged tetragermadiene precursor (A2Ge=GeB-X-BGe=GeA2), heavier acyclic diene metathesis polymerization occurs, in analogy to the widespread acyclic diene metathesis (ADMET) polymerization in the carbon case, yielding a polydigermene. The metathesis of carbon–carbon double bonds is an important tool in organic synthesis and now a similar reshuffling has been carried out with heavier alkene analogues featuring unsymmetrically substituted Ge=Ge double bonds. This reaction enables the synthesis of symmetric molecular digermenes as well as a polymer based on Ge=Ge repeat units.

Herein, we report the origin of unexpected reactivity of bicyclo[4.2.0]oct-6-ene substrates containing an α,β-unsaturated amide moiety in ruthenium-catalyzed alternating ring-opening metathesis polymerization reactions. Specifically, compared with control substrates bearing an ester, alkyl ketone, nitrile, or tertiary amide substituent, α,β-unsaturated substrates with a weakly acidic proton showed increased rates of ring-opening metathesis mediated by Grubbs-type ruthenium catalysts. 1H NMR and IR spectral analyses indicated that deprotonation of the α,β-unsaturated amide substrates resulted in stronger coordination of the carbonyl group to the ruthenium metal center. Principal component analysis identified ring strain and the electron density on the carbonyl oxygen (based on structures optimized by means of ωB97X-D/6311+G(2df,2p) calculations) as the two key contributors to fast ring-opening metathesis of the bicyclo[4.2.0]oct-6-enes; whereas the dipole moment, conjugation, and energy of the highest occupied molecular orbital had little to no effect on the reaction rate. We conclude that alternating ring-opening metathesis polymerization reactions of bicyclo[4.2.0]oct-6-enes with unstrained cycloalkenes require an ionizable proton for efficient generation of alternating polymers.

There is growing interest in the detection of bacteria in consumables, for example, in the food and water sectors. In this study, the aim was to produce a polymer-based bacteria biosensor via ROMP (ring opening metathesis polymerization). In the first part of the study, block and random copolymers were synthesized, and their biocidal activities were tested on the glass surface. Interdigitated electrode arrays coated with the polymers possessing the highest activity were used to screen the affinity towards different bacterial strains by monitoring impedance variations in real-time. The polymer-coated electrode could detect gram-positive and gram-negative bacteria strains at a concentration of 10(7) cfu/mL. The results show that ROMP-based polymer offers bacterial detection and can be used in developing biosensor devices for efficiently detecting pathogenic bacteria.

A promising solution to address the challenges in plastics sustainability is to replace current polymers with chemically recyclable ones that can depolymerize into their constituent monomers to enable the circular use of materials. Despite some progress, few depolymerizable polymers exhibit the desirable thermal stability and strong mechanical properties of traditional polymers. Here we report a series of chemically recyclable polymers that show excellent thermal stability (decomposition temperature >370 °C) and tunable mechanical properties. The polymers are formed through ring-opening metathesis polymerization of cyclooctene with a trans-cyclobutane installed at the 5 and 6 positions. The additional ring converts the non-depolymerizable polycyclooctene into a depolymerizable polymer by reducing the ring strain energy in the monomer (from 8.2 kcal mol-1 in unsubstituted cyclooctene to 4.9 kcal mol-1 in the fused ring). The fused-ring monomer enables a broad scope of functionalities to be incorporated, providing access to chemically recyclable elastomers and plastics that show promise as next-generation sustainable materials.

We report the first total synthesis of samroiyotmycin A (1), a C2‐symmetric 20‐membered anti‐malarial macrodiolide isolated from Streptomyces sp. The convergent synthetic strategy orchestrates bisalkyne fragment‐assembly using an unprecedented Schöllkopf‐type condensation on a substituted β‐lactone and an ambitious late‐stage one‐pot alkyne cross metathesis–ring‐closing metathesis (ACM–RCAM) reaction. The demanding alkyne metathesis sequence is achieved using the latest generation of molybdenum alkylidynes endowed with a tripodal silanolate ligand framework. Subsequent conversion to the required E‐alkenes uses contemporary hydrometallation chemistry catalysed by tetrameric cluster [{Cp*RuCl}4]., Forging of the 20‐membered macrocylic core of samroiyotmycin A can be readily achieved by combining a Mo‐catalysed one‐pot alkyne cross‐metathesis ring‐closing metathesis of bisalkyne building blocks and Ru‐catalysed hydrometallation chemistry. These key transformations have enabled the first total synthesis of this anti‐malarial C 2‐symmetric macrodiolide.

The understanding and control of stereoselectivity is a central aspect in ring-opening metathesis polymerization (ROMP). Herein, we report detailed quantum chemical studies on the reaction mechanism of E-selective ROMP of norborn-2-ene (NBE) with Mo(N-2,6-Me2-C6H3)(CHCMe3)(IMes)(OTf)2 (1, IMes = 1,3-dimesitylimidazol-2-ylidene) as a first step to stereoselective polymerization. Four different reaction pathways based on an ene syn or ene anti approach of NBE to either the syn- or anti-isomer of the neutral precatalyst have been studied. In contrast to the recently established associative mechanism with a terminal alkene, where a neutral olefin adduct is formed, NBE reacts directly with the catalyst via [2 + 2] cycloaddition to form molybdacyclobutane with a reaction barrier about 30 kJ mol-1 lower in free energy than via the formation of a catalyst-monomer adduct. However, the direct cycloaddition of NBE was only found for one out of four stereoisomers. Our findings strongly suggest that this stereoselective approach is responsible for E-selectivity and point toward a substrate-specific reaction mechanism in olefin metathesis with neutral Mo imido alkylidene N-heterocyclic carbene bistriflate complexes.

Since recycling of polymers is a preferred means of reducing unwanted wastes and land-filling activity, and recovering monomers or other materials of economic value, tertiary methods of recycling (chemical recycling) have been critically reviewed, giving special attention, in each case, to the chemical basis of the particular recycling pathway and its potential applicability. Recycling issues of each of the widely used commodity polymers � polyesters, polyamides, polyurethanes, epoxies, poly(vinyl chloride), polystyrene, and polyolefins � have been discussed individually, giving attention to both conventional and unconventional methods of perceived high potential, such as enzymatic degradation, ionic liquids mediation, microwave irradiation, and treatment in super critical liquids as well as super fluids. In addition, novel emerging methods undergoing greater study at present, such as cross-alkane metathesis (CAM), tandem hydrogenolysis/aromatization, vitrimer-based recycling, and dynamic covalent bonding are also highlighted. © 2021 Kingfa Scientific and Technological Co. Ltd.

A well-defined intermolecular toluene complex of lead(II) supported by a pincer-type saNHC (saturated N-heterocyclic carbene) ligand was prepared through deprotonation of the bis(imidazolinium) salt with Pb[N(SiMe3)2]2 or metalation of the free carbene and subsequent salt metathesis with Tl(OTf), followed by crystallization from toluene. Combined computational and experimental results indicate that noncovalent interactions with the lead atom (σ-sss-hole type interaction, dispersion) and the diisopropylphenyl side groups of the ligand (dispersion) stabilize the complex.

Summary The selective functionalization of methane under ambient conditions remains a formidable challenge for chemists. While most studies have focused on transition metal complexes, much less attention has been devoted to molecular complexes based on non-metal elements, despite them being more sustainable and less environmentally impactful. Here, we report that an N-heterocyclic carbene-stabilized borenium complex can activate methane under relatively mild conditions. The resulting methylborenium complex can readily transfer the methyl group to catecholborane (HBcat), which can lead to a synthetic cycle for the conversion of methane to MeBcat. Both experimental and theoretical mechanistic studies suggest that the C–H bonds of methane are activated via a σ-bond metathesis pathway. Such direct aliphatic C–H borylation can be extended to other alkanes, such as ethane and octane. The formed alkylborenium complexes can react with terminal alkynes via 1,2-alkylboration to install both the alkyl and boryl functionalities onto organic scaffolds.

The first total synthesis of the actin‐stabilizing marine natural product geodiamolide H was achieved. Solid‐phase based peptide assembly paired with scalable stereoselective syntheses of polyketide building blocks and an optimized esterification set the stage for investigating the key ring‐closing metathesis. Geodiamolide H and synthetic analogues were characterized for their toxicity and for antiproliferative effects in cellulo, by characterising actin polymerization induction in vitro, and by docking on the F‐actin target and property computation in silico, for a better understanding of structure‐activity relationships (SAR). A non‐natural analogue of geodiamolide H was discovered to be most potent in the series, suggesting significant potential for tool compound design., The F‐actin stabilizing natural product geodiamolide H and its analogues were comprehensively investigated. The first total synthesis of geodiamolide H was enabled by optimized, scalable building block synthesis, improved couplings, and by a ring‐closing metathesis as a key step. Biological profiling of the synthesized library in cells, on target, and in silico uncovered potent and simplified non‐natural analogues. Additional structure‐activity relationship information was extracted for the whole class, useful for tool compound design.

The study of the P3HT synthesis was carried out to investigate the effect of reaction time on thermal, optical, electronic, and morphological properties. It has been demonstrated that the variation in polymerization time over 30 min did not significantly affect the optoelectronic properties of polymers. Regarding the thermal properties, the P3HT synthesized in the shortest time presented a decomposition temperature of 20 K higher than the others. There was no difference in glass transition temperature or melting temperature, while both crystallization temperature and crystallinity content have slightly increased with polymerization time. The regioregularity of all polymers was 98%. The advantage is that a short reaction time is possible to obtain a polymer with suitable properties and, consequently, savings in the process. P3HT-30 was evaluated in a PSC active layer with the configuration of ITO/PEDOT: PSS/rrP3HT:PC71BM/Ca/Al, and PCE was 1.94%.

Ir‐catalyzed asymmetric alkene hydrogenation is presented as the strategy par excellence to prepare saturated isoprenoids and mycoketides. This highly stereoselective synthesis approach is combined with an established 13C‐NMR method to determine the enantioselectivity of each methyl‐branched stereocenter. It is shown that this analysis is fit for purpose and the combination allows the synthesis of the title compounds with a significant increase in efficiency., Cyclo‐archaeol, iso‐caldarchaeol, caldarchaeol, and mycoketide are prepared by employing asymmetric hydrogenation to generate the multiple stereocenters.

Nanostructured tricontinuous block polymers allow for the preparation of single-component materials that combine multiple properties. We demonstrate the synthesis of a mesoporous material from the selective orthogonal etching of a microphase-separated tricontinuous block polymer precursor. Using the synthetic approach of polymerization-induced microphase separation (PIMS), divinylbenzene (DVB) is polymerized from a mixture of poly(isoprene) (PI) and poly(lactide) (PLA) macro-chain transfer agents. In the PIMS process in situ cross-linking by the DVB arrests structural coarsening, resulting in a disordered block polymer morphology that we posit exhibits three nonintersecting continuous domains. Selective etching of the PI domains by olefin cross metathesis and PLA domains by hydrolytic degradation produces a mesoporous polymer with two independent pore networks arising from the different etch mechanisms.

Vitrimers make up a class of polymeric materials combining the advantages of thermosets and thermoplastics, because they can be reprocessed while being at the same time permanently cross-linked. However, a long heating duration or an elevated temperature is necessary for most vitrimers to relax the stress from deformation and exhibit malleability. Herein, a disulfide-containing carboxylic acid is applied as a curing agent to synthesize epoxy vitrimers with simultaneous disulfide metathesis and carboxylate transesterification. The insoluble networks exhibit rapid stress relaxation and have relaxation times ranging from 1.5 s (200 °C) to 5500 s (60 °C), while the temperature of malleability is as low as 65 °C. Moreover, this vitrimer can be efficiently reprocessed at 100 °C in 1 h with full recovery of mechanical strength for at least four cycles. Additionally, such a material is simply synthesized from commercially available chemicals and may have potential applications in the electronics industry where a high temperature is not allowed.

Ring-opening metathesis polymerization (ROMP) of buckybowl corannulene-based oxa-norbornadiene monomer is shown to give rise to polymeric nanomaterials with an average pore size of about 1.4 nm and a surface area of 49.2 m2/g. Application in supercapacitor devices show that the corannulene-based nanomaterials exhibit a specific capacitance of 134 F·g–1 (1.0 V voltage window) in a three-electrode cell configuration. Moreover, the electrode assembled from these materials in a symmetric configuration (1.6 V voltage window) exhibits long-term cyclability of 90% capacitance retention after undergoing 10000 cycles. This work demonstrates that ROMP is a valuable method in synthesizing nanostructured corannulene polymers, and that materials based on the nonplanar polycyclic aromatic motif represents an attractive active component for fabrication of devices targeted at electrochemical energy storage applications. Accepted version

The synthesis of five-coordinate amido hydride PSiP pincer complexes of both RhIII and IrIII was pursued. The preparation of such complexes by a salt metathesis route was initially targeted to asse...

Stereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal-mediated ring-opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal-free ROMP. Ion-pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB with trans alkene content of 25 to >98 %. High cis content was obtained from relatively larger counterions, toluene as solvent, low temperatures (-78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with high trans content. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control.

A chiral anion-mediated asymmetric Heck/Tsuji-Trost reaction of aryl iodides and 1,3-dienes is presented. Chiral indoline derivatives could be afforded with remarkably higher yields and enantioselectivities than our previous chiral ligand-based method. Silver carbonate is employed as both base and halide scavenger to ensure fast and recyclable exchange of the catalytic amount of chiral anions. Fast salt metathesis, as well as the acceleration effect of the chiral anion, could both benefit the stereocontrol of the reaction.

Metal-mediated σ-bond metathesis and σ-complex-assisted metathesis (σ-CAM) reactions represent a major class of alkane C–H activation reactions. Here, we present quasiclassical direct dynamics traj...

The total synthesis of viridiofungins A (1) and B (2) via β-lactone 3 in 13 steps is reported. Key steps included an HF-mediated rearrangement of cyclobutene diester 9 to form a bicyclic lactone 6, an olefin cross metathesis between disubstituted alkene 3 and alkene 4 in which isomerization was suppressed, and a novel β-lactone ring opening to form the amide. Deprotection then gave either viridiofungin A (1) or B (2) in high yield.

The total synthesis of haliclonin A was accomplished. Starting from 3,5-dimethoxybenzoic acid, a functionalized cyclohexanone fused to a 17-membered ring was prepared through a Birch reduction/alkylation sequence, ring-closing metathesis, intramolecular cyclopropanation, and stereoselective 1,4-addition of an organocopper reagent to an enone moiety. Reductive C-N bond formation via an N , O -acetal forged the 3-azabicyclo[3.3.1]nonane core. The allyl alcohol moiety was constructed by a sequence involving stereoselective α-selenylation of an aldehyde via an enamine, syn -elimination of a selenoxide, and allylation of the aldehyde with an allylboronate. Formation of the 15-membered ring containing a skipped diene was achieved by ring-closing metathesis, and final transformations led to the synthesis of haliclonin A.

Non-canonical amino acid derivatives are an attractive scaffold for novel drug candidates. Among the methods used to prepare this motif, the asymmetric Mannich-type reaction of α-imino carboxylic acid derivatives is a preeminent strategy because a wide variety of non-canonical amino acids can be accessed by changing only the nucleophile. Preparing the common substrate is difficult, however, which makes this method problematic. We developed a convenient method for synthesizing common substrates using MnO2-mediated oxidation of stable precursors. Peptides bearing non-canonical amino acids are another attractive synthetic target. We propose a new approach for synthesizing non-canonical amino acid-containing peptides by directly applying various organic reactions to peptidic substrates. Using hydrophobic anchor-supported peptides, we directly applied ring-closing metathesis and asymmetric Friedel–Crafts reactions to peptidic substrates. We also developed a novel recyclable organocatalyst according to the nature of the hydrophobic anchor tagged compound.

Although gem-diborylalkenes are known to be among the most valuable reagents in modern organic synthesis, providing a rapid access to a wide array of transformations, including the construction of C-C and C-heteroatom bonds, their use as dienophile-reactive groups has been rare. Herein we report the Diels-Alder (DA) reaction of (unsymmetrical) gem-diborylalkenes. These reactions provide a general and efficient method for the stereoselective conversion of gem-diborylalkenes to rapidly access 1,1-bisborylcyclohexenes. Using the same DA reaction manifold with borylated-dienes and gem-diborylalkenes, we also developed a concise, highly regioselective synthesis of 1,1,2-tris- and 1,1,3,4-tetrakis(boronates)cyclohexenes, a family of compounds that currently lack efficient synthetic access. Furthermore, DFT calculations provided insight into the underlying factors that control the chemo-, regio-, and stereoselectivity of these DA reactions. This method also provides stereodivergent syntheses of gem-diborylnorbornenes. The utility of the gem-diborylnorbornene building blocks was demonstrated by ring-opening metathesis polymerization (ROMP), providing a highly modular approach to the first synthesis of the gem-diboron-based polymers. Additionally, these polymers have been successfully submitted to postpolymerization modification reactions. Given its simplicity and versatility, we believe that this novel DA and ROMP approach holds great promise for organoboron synthesis as well as organoboron-based polymers and that it will result in more novel transformations in both academic and industrial research.

A series of thia-bridged triarylamine[4]helicene-functionalized polynorbornenes P1, P2, and P3 were synthesized via ring-opening metathesis polymerization (ROMP). The polymers obtained undergo a reversible one-electron oxidation, in both solution and solid state, responding to the pH changes in the surrounding medium showing a clear reversible electrochromic behavior.

Herein, we report the enantiospecific synthesis of two artificial glutamate analogs designed based on IKM-159, an antagonist selective to the AMPA-type ionotropic glutamate receptor. The synthesis features the chiral resolution of the carboxylic acid intermediate by the esterification with ʟ-menthol, followed by a configurational analysis by NMR, conformational calculation, and X-ray crystallography. A mice in vivo assay showed that (2R)-MC-27, with a six-membered oxacycle, is neuroactive, whereas the (2S)-counterpart is inactive. It was also found that TKM-38, with an eight-membered azacycle, is neuronally inactive, showing that the activity is controlled by the ring C.

Vanadium-based catalysts have shown activity and selectivity in ring-opening metathesis polymerization of strained cyclic olefins comparable to those of Ru, Mo, and W catalysts. However, the application of V alkylidenes in routine organic synthesis is limited. Here, we present the first example of ring-closing olefin metathesis catalyzed by well-defined V chloride alkylidene phosphine complexes. The developed catalysts exhibit tolerance to various functional groups, such as an ether, an ester, a tertiary amide, a tertiary amine, and a sulfonamide. The size and electron-donating properties of the imido group and the phosphine play a crucial role in the stability of active intermediates. Reactions with ethylene and olefins suggest that both 𝛽-hydride elimination of the metallacyclobutene and bimolecular decomposition are responsible for catalyst degradation.

We introduce the synthesis of long-chain aliphatic metathesis polymers containing trimethyl-locked benzoquinone (TMBQ) as a redox-responsive functional unit. Specifically, we demonstrate that this moiety, placed in each repeating unit within the polymer, enables the on-demand degradation of the polymer into small molecules upon the addition of a reductant such as Na2S2O4. Notably, the cleaved TMBQ unit is recovered with high purity, hereby facilitating the synthesis of recyclable redox polymers. Importantly, we expand the scope of possible applications by postpolymerization modification of the olefinic backbone with bromine and pentafluorophenyl motifs, affording redox polymers with tailored functional properties.

Quantum mechanical calculations on the mechanism of olefin metathesis with a variety of substituents mediated by a Ru alkylidene catalyst reveal multistep processes along the general reactants → ad...

Polyolefin waste is constantly growing, and the few existing solutions for recycling, reuse, and degradation are not viable long term. Carbon–carbon bond scission is a highly sought-after technology to assist in reclaiming polymers. This work compiles and advances the understanding of β-alkyl elimination, a method of C–C cleavage, through DFT characterization on a model substrate, (S)-2,8-dimethyldecane, and silica-supported Zr–H catalyst, [(SiO)3ZrH]. The primary goal is to examine selectivity in C–C bond cleavage events. σ-Bond metathesis favors C–H activation at methyl branches by ∼2 kcal mol−1. Chain walking via β-H elimination and insertion occurs readily and prefers E-alkene eliminations. β-Alkyl elimination also favors formation of E-alkene elimination products (∼2 kcal mol−1), β-Me elimination (∼1 kcal mol−1), and primary Zr–C cleavage (∼2 kcal mol−1) over Z-alkenes, β-R (R > CH3) elimination, and secondary Zr–C cleavage, respectively. These selectivity rules will help guide future experimental work and catalyst design.

Templated polymerization is a process whereby the molecular weight and dispersity of a parent polymer can be mirrored onto a second, daughter polymer. While ubiquitous in nature and explored in bio-inspired polymers, templated synthesis has scarcely been used towards the controlled synthesis of conjugated polymers. Conjugated polymers are useful for electronic and optical applications, yet very few examples can be prepared in a controlled manner. Here we show that it is possible to use ring-opening metathesis polymerization to prepare macromolecular templates with controlled molecular weights and dispersities. Chemical oxidative polymerization is then used to prepare the final well-defined conjugated polymers. By combining these techniques, we demonstrate a versatile approach to well-defined conjugated polymers, where traditional synthetic routes are generally limited in control and/or scope. Templated oxidative polymerization affords organic soluble, oxidatively doped PEDOT-based polymers with controlled molecular weights and low dispersities (Đ ∼ 1.2). To our knowledge, this is the first report of a templated approach being used to definitively control the molecular weight, dispersity, and solubility of conjugated polymers during oxidative polymerization.

High molar mass poly(ricinoleic acid) with a weight average molar mass over 400 kg mol−1 was synthesized via entropy-driven ring-opening metathesis polymerization of mono-, di- and mixed macrolactones of ricinoleic acid using a Grubbs second-generation catalyst and fully characterized. The high molar mass was achieved by reducing the catalyst loading, and the resultant polymer product had a very low level of ruthenium (36 ppm as Ru based on G2 feed), was colorless and exhibited a high decomposition temperature without purification steps aimed at removing ruthenium.

The direct, graft-through, ring-opening metathesis polymerisation (ROMP) of unprotected DNA macromonomers is reported. By tuning the polymerisation conditions, good control is achieved, enabling the rapid and efficient synthesis of DNA-containing bottlebrush copolymers, without the need for protection of the DNA bases.

Long-standing conventional synthetic methods limit the scope of polymer architectural design such as connectivity, sequence and symmetry. Herein, we report a series of star gradient copolymers with variable grafting densities and backbone lengths. These star copolymers were obtained by one-shot ring-opening metathesis polymerization (ROMP) of an ω-norbornenyl polystyrene macromonomer (PS) and an endo-norbornenyl penta-fluorophenyl ester monomer (PFP), mediated by the highly active Blechert's type three-arm olefin metathesis catalyst. The kinetic studies of the copolymerization process revealed that a gradient sequence distributed along the star backbone and the tapered structure changed with the feed ratio between the PS and PFP. These copolymers were further modified with the activated ester chemistry to afford novel star-polymer-based functional materials.

The synthesis and reactivity of dialkynyldiboranes(4), a little-studied family of diboranes, are presented herein. Three dialkynyldiboranes(4) were prepared via two different salt metathesis pathways. The three reactive sites of these dialkynyldiboranes(4) are then selectively addressed by judicious application of reagents: addition of an amine N-oxide leads to oxygen insertion into the B–B bond, dicobaltoctacarbonyl binds to the alkynyl CC bonds, while Sonogashira–Hagihara cross-coupling conditions lead to double C–C bond formation at the alkynyl C–H groups.

Metathesis copolymerization of 1-(p-trimethylsilyl)phenyl-1-propyne with diphenylacetylenes was achieved and the gas permeability of polymer membranes was improved by the incorporation of 20% phenylpropyne unit.

The incorporation of strained alkynes into polymers is generally achieved by employing step-growth polymerization methods or post-polymerization reactions. Here, we demonstrate that cyclopropenone-masked strained alkynes are tolerant to chain-growth ring-opening metathesis polymerization, and that, upon post-polymerization photochemical demasking with loss of CO, the strained alkyne group appended to each repeating unit can be used to prepare functional (e.g., fluorescent or redox-active) polymers from a common polymer backbone. We support our claims about polymer transformations throughout the manuscript through the inclusion of a complete set of model reactions and characterization data for analogous molecular species. The findings of this study are transferable to other polymeric systems, opening the door to the creation of libraries of multifunctional chain-growth polymers with identical polymer backbones.

The synthesis of nine-membered rings via alkyne–carbonyl metathesis is reported. The alkyne and acetal units contained in a biaryl substrate undergo the intramolecular alkyne–carbonyl metathesis reaction under FeCl3-catalysis to furnish the unexplored 6,7-dihydro-5H-dibenzo[c,e]azonines. The method provides an alternative to existing routes to nine-membered rings with cheap, non-toxic iron catalysts and milder conditions.