Cross-metathesis Reaction Research Articles

A Versatile Synthesis of Pentacosafuranoside Subunit Reminiscent of Mycobacterial Arabinogalactan Employing One Strategic Glycosidation Protocol.

Oligosaccharides are involved in a myriad of biological phenomena. Many glycobiological experiments can be undertaken if homogenous and well-defined oligosaccharides are accessible. Mycobacterial cell walls contain arabinogalactan as one of the major constituents that is challenging for chemical synthesis. Therefore, the major aim of this investigation is to synthesise a major oligosaccharide portion of the arabinogalactan. The pentacosafuranoside (25mer) synthesis involved installation of several arabinofuranosidic linkages through neighbouring group participation for 1,2-trans linkages and oxidation-reduction strategy for the 1,2-cis Araf. A strategically placed n-pentenyl moiety at the reducing end enables ligation of biomolecular probes through celebrated cross metathesis or thiol-ene click reactions. Several linear and branched oligosaccharides were synthesised ranging from trisaccharide to pentadecasaccharide during this endeavour. Synthesis of pentacosasaccharide was accomplished in 77 steps with 0.0012 % overall yield. These oligosaccharides are envisioned to be excellent probes for understanding disease biology thereby facilitating discovery of novel antitubercular agents, vaccines and/or diagnostics.

Stereoselective synthesis of (−)-synargentolide B

A convergent, enantioselective total synthesis of (−)-synargentolide-B has been accomplished from readily available l-arabinose and d-ethyl lactate by a 10-step sequence involving Still-Gennari olefination, one-pot acidic deprotection/lactonization and olefin cross-metathesis reaction as the key step.

Control of Molecular Weight and End-Functional Groups of Polyester from A2 + B2 Polycondensation via Cross-Metathesis of Cyclic Unsaturated Polyester with Difunctional Olefin

As an approach to control the molecular weight and polymer end groups of polyester obtained by A2 + B2 polycondensation, we investigated cross-metathesis of cyclic polyesters containing carbon–carbon double bonds in the backbone with a symmetric olefin having two functional groups as an exchange reagent (ExR). Polycondensation of cis-2-butene-1,4-diol (1) and sebacoyl dichloride (4) did not selectively afford cyclic polyester, but when cis- or trans-4-octene-1,8-diol, instead of 1, was reacted with 4 or isophthaloyl dichloride, we found that cyclic unsaturated polyesters were formed selectively. The obtained cyclic polyesters successfully underwent cross-metathesis reaction with cis-1,4-diacetoxy-2-butene (6) in the presence of second-generation Grubbs catalyst to afford linear polyester bearing acetoxy groups at both ends. The molecular weight of the linear polyester decreased with increasing amount of 6 regardless of the molecular weight of the starting cyclic polyester; the molecular weight of the resu...

Synthesis of E- and Z-trisubstituted alkenes by catalytic cross-metathesis.

Catalytic cross-metathesis is a central transformation in chemistry, and yet, corresponding methods for stereoselectively generating acyclic trisubstituted alkenes in either isomeric form do not exist. The key problems are lack of chemoselectivity, namely, the preponderance of side reactions involving only the less hindered starting alkene, ensuing nonproductive processes of homo-metathesis byproducts, and formation of short-lived methylidene complexes. In contrast, in catalytic cross-coupling, another widely used process, substrates are more distinct and homocoupling is less of a problem. Here, we show that through cross-metathesis reactions involving E- or a Z-trisubstituted alkenes, easily prepared from commercially available starting materials by cross-coupling processes, many otherwise desirable and difficult-to-access linear E- or Z-trisubstituted alkenes can be synthesized efficiently and in exceptional stereoisomeric purity (up to >98% E or 95% Z). Utility is highlighted through concise stereoselective syntheses of biologically active compounds such as indiacen B (anti-fungal) and coibacin D (anti-inflammatory).

Total Synthesis of Four Isomers of the Proposed Structures of Cryptorigidifoliol K.

The first asymmetric convergent total synthesis of four isomers of proposed structures of cryptorigidifoliol K (1a, 1b, 1c, and 1d) has been achieved from commercially available starting materials. The key steps in this synthesis involve tandem isomerization followed by a C-O and C-C bond-forming reaction for the construction of trans-2,6-disubstituted dihydropyran, iodolactonization, isomerization of terminal alkene, and cross-metathesis reaction. The large discrepancies in the spectroscopic data (1H NMR) of synthetic cryptorigidifoliol K from the natural product suggest that the structure of the natural cryptorigidifoliol K requires revision.

A Common Approach for the Synthesis of (R)‐Ethyl 2,4‐dihydroxy‐6‐(8‐hydroxynonyl) benzoate, Ethyl 2,4‐Dihydroxy‐6‐nonylbenzoate and (2R,3R)‐1,2,3,4‐Butanetetraol‐1,4‐diorsellinate

AbstractA concise and facile first total synthesis of biological active β‐resorcylic acid ester (R)‐ethyl 2,4‐dihydroxy‐6‐(8‐hydroxynonyl) benzoate, ethyl 2,4‐Dihydroxy‐6‐nonylbenzoate and (2R,3R)‐1,2,3,4‐Butanetetraol‐1,4‐diorsellinate have been demonstrated from commercially available ethyl acetoacetate as starting material. Key steps employed for the synthesis of target molecules are cross metathesis and esterification reaction.

Synthesis of Z- or E-Trisubstituted Allylic Alcohols and Ethers by Kinetically Controlled Cross-Metathesis with a Ru Catechothiolate Complex.

The first examples of kinetically controlled cross-metathesis reactions that generate Z- or E-trisubstituted alkenes are disclosed. Transformations are catalyzed by ≤6.0 mol % of a Ru catechothiolate complex and afford trisubstituted allylic alcohols and ethers in up to 81% yield and >98% stereoisomeric purity. The method has considerable scope, as olefins containing an alcohol, an aldehyde, an epoxide, a carboxylic acid, or an alkenyl group may be used. Mechanistic models that account for the observed levels and trends in efficiency and stereochemical control are provided, based on DFT studies.

Synthesis of 2-aminosuberic acid derivatives as components of some histone deacetylase inhibiting cyclic tetrapeptides.

A new synthesis of the important amino acid 2-aminosuberic acid from aspartic acid is reported. The methodology involves the alternate preparation of (S)-2-aminohept-6-enoate ester as a building block and its diversification through a cross-metathesis reaction to prepare the title compounds. The utility of the protocol is demonstrated through the preparation of three suberic acid derivatives of relevance to the design and the synthesis of peptides of biological relevance.

Study of the Cross-Metathesis Reaction of α-Hydroxy β,γ-Unsaturated Amides towards a Rapid and Flexible Total ­Synthesis of Symbioramide and its Isomer

The reactivity of novel α-hydroxy β,γ-unsaturated amides in cross-metathesis reactions was extensively studied and used to perform a short total synthesis of symbioramide and its isomer from ­l-serine methyl ester.

Retraction of “A 1,2-Dicarbadodecaborane(12)-1,2-Dithiolate Chelating Ruthenium Carbene Catalyst for Highly Z Selective Olefin Metathesis”

A highly Z selective olefin metathesis ruthenium carbene catalyst containing a 1,2-dicarbadodecaborane(12)-1,2-dithiolate ligand was synthesized, and the structure was determined by single-crystal X-ray diffraction. Due to the large steric hindrance and strong electron-withdrawing effects of the carborane ligand, the new ruthenium complex is more stable than previously reported Ru catalysts which contain benzene-1,2-dithiolate ligands. The new ruthenium carbene catalyst can catalyze cross-metathesis (CM) reactions of terminal alkenes with (Z)-but-2-ene-1,4-diol and CM reactions of other terminal alkenes to give highly Z selective products in moderate to good yields. In addition, the catalyst was also able to catalyst a ring-closing metathesis (RCM) reaction to give a macrocyclic ring compound with a (Z)-olefin structure as the major product. Like other ruthenium carbene catalysts, the new complex tolerates many different functional groups.

Single-phase block copolymers by cross-metathesis of 1,4-cis-polybutadiene and 1,4-cis-polyisoprene

Macromolecular Cross-Metathesis (MCM) reactions on commercial Polybutadiene (PBD) and Polyisoprene (PIP) homopolymers, in the presence of first generation Grubbs and Hoveyda-Grubbs catalysts, are reported. 13C-NMR resonances of butadiene(B)/isoprene(I) heterosequences show block-copolymer formation, with blocks longer than a hundred monomer units, even for long reaction times. DSC scans of MCM products show that, with MCM time, PBD crystallinity progressively disappears while the well separated Tg of the two homopolymers merge to an intermediate single Tg. This indicates that PBD and PIP blocks are completely miscible when their lengths are reduced to a few hundred units. 13C NMR spectra also show that, for the considered MCM process, double bond isomerizations are definitely more frequent than heterosequence formations.

Catalytic Asymmetric Synthesis and Stereochemical Revision of (+)-Cryptoconcatone H.

The total synthesis and structural revision of (+)-cryptoconcatone H are described. Guided by computational studies for the final structure assignment, the stereogenic centers at the tetrahydropyran moiety of (+)-cryptoconcatone H were assembled through catalytic asymmetric methodologies: Krische allylation, cross-metathesis reaction, and THP formation via Pd(II)-catalyzed cyclization. Finally, a Krische allylation reaction established the last stereocenter, and the lactone moiety was formed by ring-closing metathesis.

A One-Pot Methodology for the Synthesis of the Yohimban Skeleton

A simple and straightforward assembly of the yohimban skeleton was achieved by condensation of an acyclic β-keto ester with tryptamine, followed by consecutive cross metathesis and tandem cyclization reactions, leading to the formation of three new rings. The whole process was readily carried out in the one-flask providing a rapid entry to the pentacyclic scaffold of yohimbine alkaloids.

In Situ Methylene Capping: A General Strategy for Efficient Stereoretentive Catalytic Olefin Metathesis. The Concept, Methodological Implications, and Applications to Synthesis of Biologically Active Compounds.

In situ methylene capping is introduced as a practical and broadly applicable strategy that can expand the scope of catalyst-controlled stereoselective olefin metathesis considerably. By incorporation of commercially available Z-butene together with robust and readily accessible Ru-based dithiolate catalysts developed in these laboratories, a large variety of transformations can be made to proceed with terminal alkenes, without the need for a priori synthesis of a stereochemically defined disubstituted olefin. Reactions thus proceed with significantly higher efficiency and Z selectivity as compared to when other Ru-, Mo-, or W-based complexes are utilized. Cross-metathesis with olefins that contain a carboxylic acid, an aldehyde, an allylic alcohol, an aryl olefin, an α substituent, or amino acid residues was carried out to generate the desired products in 47-88% yield and 90:10 to >98:2 Z:E selectivity. Transformations were equally efficient and stereoselective with a ∼70:30 Z-:E-butene mixture, which is a byproduct of crude oil cracking. The in situ methylene capping strategy was used with the same Ru catechothiolate complex (no catalyst modification necessary) to perform ring-closing metathesis reactions, generating 14- to 21-membered ring macrocyclic alkenes in 40-70% yield and 96:4-98:2 Z:E selectivity; here too, reactions were more efficient and Z-selective than when the other catalyst classes are employed. The utility of the approach is highlighted by applications to efficient and stereoselective syntheses of several biologically active molecules. This includes a platelet aggregate inhibitor and two members of the prostaglandin family of compounds by catalytic cross-metathesis reactions, and a strained 14-membered ring stapled peptide by means of macrocyclic ring-closing metathesis. The approach presented herein is likely to have a notable effect on broadening the scope of olefin metathesis, as the stability of methylidene complexes is a generally debilitating issue with all types of catalyst systems. Illustrative examples of kinetically controlled E-selective cross-metathesis and macrocyclic ring-closing reactions, where E-butene serves as the methylene capping agent, are provided.

Synthesis of new multiblock copolymers via cross-metathesis reaction of polytrimethylsilylnorbornene and polycyclooctene

The cross-metathesis reaction between polytrimethylsilylnorbornene and polycyclooctene is investigated for the first time. Using the Grubbs Ru-carbene complex of the first generation, the synthesis of random multiblock copolymers of trimethylsilylnorbornene and cyclooctene is carried out. The effect of the reaction conditions on the block length and thermal and crystalline properties of new copolymers is studied by NMR, GPC, and DSC methods. With the use of in situ 1Н NMR spectroscopy, the kinetics of the crossmetathesis reaction is investigated. As for unsubstituted polynorbornene (Polym. Sci., Ser. B 58, 292 (2016)), the catalyst interacts initially with polycyclooctene, giving a polymer carbene complex [Ru]=PCO. Further, this complex attacks the polytrimethylsilylnorbornene chain via cross reaction with formation of complex [Ru]=PNB-Si and a diblock copolymer of trimethylsilylnorbornene and cyclooctene as reaction products. The subsequent cross reactions form a multiblock copolymer with gradually increasing block length. Throughout the entire process, the concentration of [Ru]=PCO exceeds the concentration of [Ru]=PNB-Si by more than two orders of magnitude. Simultaneously, the total concentration of carbene complexes decreases in time through their decay. The reaction kinetics is satisfactorily described by a model proposed previously for interaction between polycyclooctene and polynorbornene.

Synthesized biofuel meets vehicle standards

Researchers in Germany have developed chemical reactions that convert rapeseed oil and ethylene to a diesel fuel that could power conventional automobiles and trucks (Sci. Adv. 2017, DOI: 10.1126/sciadv.1602624). Biofuels derived from vegetable oils are often used as minor additives in conventional diesel fuel but frequently vaporize at temperatures too high to fuel vehicles on their own. Biofuels that vaporize more easily can be made from vegetable oils by hydroprocessing, a process similar to steam cracking, but the method is energy-intensive and expensive. Lukas J. Goossen of Ruhr University Bochum and coworkers have now identified palladium and ruthenium catalysts that accelerate isomerization and cross-metathesis reactions that make low-temperature-vaporizing diesel fuel from rapeseed oil. The reactions run at low temperature (60 °C), require no solvents, and produce no waste. They react fatty acid methyl esters from the oil with ethylene, potentially from bioethanol or shale gas, to form ester- and olefin-based

Ruthenium Promoted On-DNA Ring-Closing Metathesis and Cross-Metathesis.

DNA-encoded library technology (ELT) is now widely used in pharmaceutical, biotechnological, and academic research for hit identification and target validation. New on-DNA reactions are keys to exploring greater chemical space and accessing challenging chemotypes such as configurationally constrained macrocycles. Herein, we describe the first on-DNA ring-closing metathesis (RCM) and cross-metathesis (CM) reactions promoted by fast initiating Grubbs Ru reagents. Under the optimized conditions, MgCl2 was used to protect the DNA from Ru-induced decomposition. The substrate scope for on-DNA RCM was established and the same conditions were applied to a CM reaction with good conversion.

Total Syntheses of Malabaricones B and C via a Cross-Metathesis Strategy.

The malabaricones A-D belong to the class of diarylnonanoids isolated from the Myristicaceae family of plants. Although malabaricone C displayed various interesting biological activities, its isolation remains tedious due to its close chemical similarity to malabaricones A, B, and D. Therefore, development of an efficient synthesis route has become essential to cater to the need of large amounts of malabaricone C for its pharmacological profiling. So far there is only one report of the synthesis of malabaricone C through a lengthy sequence of reactions. We have developed an efficient and short route for the syntheses of malabaricones B and C, which will also provide a convenient access to all other members of the malabaricone family. Synthesis of an important building block, ω-aryl heptyl bromide, employed in the synthesis was realized by adopting a cross-metathesis reaction as the key step.

Identification of selective inhibitors of sphingosine kinases 1 and 2 through a structure–activity relationship study of 4-epi-jaspine B

We recently reported that 4-epi-jaspine B exhibits potent inhibitory activity towards sphingosine kinases (SphKs). In this study, we investigated the effects of modifying the 2-alkyl group, as well as the functional groups on the THF ring of 4-epi-jaspine B using a diversity-oriented synthesis approach based on a late-stage cross metathesis reaction. The introduction of a p-phenylene tether to the alkyl group was favored in most cases, whereas the replacement of a carbon atom with an oxygen atom led to a decrease in the inhibitory activity. Furthermore, the introduction of a bulky alkyl group at the terminus led to a slight increase in the inhibitory activity of this series towards SphKs compared with 4-epi-jaspine B (the Q values of compound 13 for SphK1 and SphK2 were 0.2 and 0.4, respectively). Based on this study, we identified two isoform selective inhibitors, including the m-phenylene derivative 4 [IC50 (SphK1) ≥30μM; IC50 (SphK2)=2.2μM] and the methyl ether derivative 22 [IC50 (SphK1)=4.0μM; IC50 (SphK2) ≥30μM].

Construction of Well-Defined Redox-Responsive CO2 -Based Polycarbonates: Combination of Immortal Copolymerization and Prereaction Approach.

Due to the axial group initiation in traditional (salen)CoX/quaternary ammonium catalyst system, it is difficult to construct single active center propagating polycarbonates for copolymerization of CO2 /epoxides. Here a redox-responsive poly(vinyl cyclohexene carbonate) (PVCHC) with detachable disulfide-bond backbone is synthesized in a controllable manner using (salen)CoTFA/[bis(triphenylphosphine)iminium, [PPN]TFA binary catalyst, where the axial group initiation is depressed by judiciously choosing 3,3'-dithiodipropionic acid as starter. While for those comonomers failing to obtain polycarbonate with unimodal gel permeation chromatography (GPC) curve, a versatile method is developed by combination of immortal copolymerization and prereaction approach, and functional aliphatic polycarbonates having well-defined architecture and narrow polydispersity can be prepared. The resulting PVCHC can be further functionalized with alkenes by versatile cross-metathesis reaction to tune the physicochemical properties. The combination of immortal polymerization and prereaction approach creates a powerful platform for controllable synthesis of functional CO2 -based polycarbonates.