Effect of Chain Structure on the Various Properties of the Copolymers of Fluorinated Norbornenes with Cyclooctene

Fluorinated polymers are attractive due to their special thermal, surface, gas separation, and other properties. In this study, new diblock, multiblock, and random copolymers of cyclooctene with two fluorinated norbornenes, 5-perfluorobutyl-2-norbornene and N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide, are synthesized by ring-opening metathesis copolymerization and macromolecular cross-metathesis in the presence of the first- to third-generation Grubbs' Ru-catalysts. Their thermal, surface, bulk, and solution characteristics are investigated and compared using differential scanning calorimetry, water contact angle measurements, gas permeation, and light scattering, respectively. It is demonstrated that they are correlated with the chain structure of the copolymers. The properties of multiblock copolymers are generally closer to those of diblock copolymers than of random ones, which can be explained by the presence of long blocks capable of self-organization. In particular, diblock and multiblock fluorine-imide-containing copolymers show a tendency to form micelles in chloroform solutions well below the overlap concentration. The results obtained may be of interest to a wide range of researchers involved in the design of functional copolymers.

Formation of Bifunctional Octasilsesquioxanes via Silylative Coupling and Cross-Metathesis Reaction

Bifunctional silsesquioxanes create an attractive group of compounds with a wide range of potential applications, and recently they have gained much interest. They are known to be obtained mainly via hydrosilylation, but we disclose novel synthetic protocols based on different but complementary reactions, i.e., cross-metathesis (CM) and silylative coupling (SC). A series of cubic T₈ type silsesquioxane derivatives with a broad scope of styryl substituents were synthesized in a one-pot procedure and characterized by spectroscopic and spectrometric methods. All of the new compounds can be obtained in a one-pot manner, which has an attractive impact on the synthetic procedure, as it is economic in terms of the isolation of intermediate products. Additionally, the methodology disclosed here enables the (E)-stereoselective introduction of styrenes derivative to the cubic T₈ type core. The presented compounds can be interesting precursors for a further functionalization that may significantly increase the possibility of their application in the design and synthesis of new functional materials.

Diversity-oriented Functionalization of Cyclodienes Through Selective Cycloaddition/Ring-opening/Cross-metathesis Protocols; Transformation of a "Flatland" into Three-dimensional Scaffolds With Stereo- and Regiocontrol

This article presents selective transformations of some readily available cyclodienes through simple chemical procedures into novel functionalized small-molecular entities. The syntheses hereby described involved selective cycloadditions, followed by ring-opening metathesis of the resulting β-lactam or isoxazoline derivatives and selective cross-metathesis by differentiation of the olefin bonds on the alkenylated heterocycles. The cross-metathesis transformations have been detailed, which were performed under various experimental conditions with the aim of exploring chemodiscrimination of the olefin bonds and delivering the corresponding functionalized β-lactam or isoxazoline derivatives.

Cross-Metathesis of Methallyl Halides: Concise Enantioselective Formal Total Synthesis of (-)-Presphaerene

The cross-metathesis (CM) of methallyl halides catalyzed using four different ruthenium-based complexes—Grubbs catalyst, Grubbs second-generation catalyst, Hoveyda-Grubbs second-generation catalyst, and Stewart–Grubbs catalyst—was investigated. When methallyl chloride or bromide was reacted with a model substrate containing a benzyl ether group, the Grubbs catalyst, and Grubbs second-generation catalyst did not promote the reaction well. However, the Hoveyda–Grubbs second-generation catalyst and Stewart–Grubbs catalyst afforded the corresponding products in moderate to good yield with moderate E/Z selectivity. Accordingly, several functionalized methallyl halides were prepared by CM. Various functional groups were well-tolerated in this system when the Stewart–Grubbs catalyst was used. To demonstrate the practical utility of our method, methallyl halide CM was successfully employed for the formal total synthesis of a natural product (–)-presphaerene, in which the precursor of the key cyclopentanecarboxylate intermediate was efficiently prepared in three steps.

Traceless Protection for More Broadly Applicable Olefin Metathesis

An operationally simple in situ protection/deprotection strategy that significantly expands the scope of kinetically controlled catalytic Z- and E-selective olefin metathesis is introduced. Prior to the addition of a sensitive Mo- or Ru-based complex, treatment of a hydroxy- or a carboxylic-acid-containing olefin with commercially available HB(pin) or readily accessible HB(trip)₂ (pin=pinacolato, trip=2,4,6-tri(isopropyl)phenyl) for 15 min is sufficient for efficient generation of a desired product. Routine workup leads to quantitative deprotection. A range of stereochemically defined Z- and E-alkenyl chlorides, bromides, fluorides, and boronates or Z-trifluoromethyl-substituted alkenes with a hydroxy or carboxylic acid group were thus prepared in 51-97 % yield with 93 to >98 % stereoselectivity. We also show that, regardless of whether a polar functional unit is present or not, a small amount of HB(pin) may be used to remove residual water, significantly enhancing efficiency.

Borane-Catalyzed Cross-Metathesis Strategy for Facile Transformation of Cyclic (Alkyl)(Amino)Germylenes

A borane B(C₆ F₅ )₃ -catalyzed metathesis reaction between the Si-C bond in the cyclic (alkyl)(amino)germylene (CAAGe) 1 and the Si-H bond in a silane (R₃ SiH; 2) is reported. Mechanistic studies propose that the initial step of the reaction involves Si-H bond activation to furnish an ionic species [1-SiR₃ ]⁺ [HB(C₆ F₅ )₃ ]^- , from which [Me₃ Si]⁺ [HB(C₆ F₅ )₃ ]^- and an azagermole intermediate are generated. The former yields Me₃ SiH concomitant with the regeneration of B(C₆ F₅ )₃ whereas the latter undergoes isomerization to afford CAAGes bearing various silyl groups on the carbon atom next to the germylene center. This strategy allows the straightforward synthesis of eight new CAAGes starting from 1.

Synthesis of a tyrosinase inhibitor by consecutive ethenolysis and cross-metathesis of crude cashew nutshell liquid

A convenient and sustainable three-step synthesis of the tyrosinase inhibitor 2-hydroxy-6-tridecylbenzoic acid was developed that starts directly from the anacardic acid component of natural cashew nutshell liquid (CNSL). Natural CNSL contains 60-70% of anacardic acid as a mixture of several double bond isomers. The anacardic acid component was converted into a uniform starting material by ethenolysis of the entire mixture and subsequent selective precipitation of 6-(ω-nonenyl)salicylic acid from cold pentane. The olefinic side chain of this intermediate was elongated by its cross-metathesis with 1-hexene using a first generation Hoveyda-Grubbs catalyst, which was reused as precatalyst in a subsequent hydrogenation step. Overall, the target compound was obtained in an overall yield of 61% based on the unsaturated anacardic acid content and 34% based on the crude CNSL.

Hyperbranched Aliphatic Polyester via Cross-Metathesis Polymerization: Synthesis and Postpolymerization Modification

A novel postpolymerization modification methodology is demonstrated to achieve selective functionalization of hyperbranched polymer (HBP). Terminal and internal acrylates of HBP derived from cross-metathesis polymerization (CMP) are functionalized in a chemoselective fashion using the thiol-Michael chemistries. Model reactions between different thiols (benzyl mercaptan and methyl thioglycolate) and acrylates (n-hexyl acrylate and ethyl trans-2-decenoate) by using dimethylphenylphosphine or amylamine as the catalyst are investigated to optimize the modification protocol for HBP. High-molecular-weight HBP P0 is generated through CMP of AB₂ monomer 2, a compound containing one α-olefin and two acrylate metathetically polymerizable groups. CMP kinetics is monitored by NMR and gel permeation chromatography (GPC). Accordingly, microstructural analysis is conducted in detail, and CMP procedure is optimized. Postpolymerization modification of HBP P0 is performed via two distinguished strategies, namely one-step complete modification and sequential modification, to generate terminally and/or internally functionalized HBPs P1-P3 in a chemoselective fashion by using phosphine-initiated and/or base-catalyzed thiol-Michael chemistries. Finally, thermal stability and glass transition behaviors of HBPs P0-P3 are studied by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively.

A succinct access to ω-hydroxylated jasmonates via olefin metathesis

In higher plants, jasmonates are lipid-derived signaling molecules that control many physiological processes, including responses to abiotic stress, defenses against insects and pathogens, and development. Among jasmonates, ω-oxidized compounds form an important subfamily. The biological roles of these ω-modified derivatives are not fully understood, largely due to their limited availability. Herein, a brief (two-step), simple and efficient (>80% yield), versatile, gram-scalable, and environmentally friendly synthetic route to ω-oxidized jasmonates is described. The approach utilizes olefin cross-metathesis as the key step employing inexpensive, commercially available substrates and catalysts.

The Influence of Acetonitrile

Kinetically controlled catalytic cross-metathesis reactions that generate (Z)-α,β-unsaturated esters selectively are disclosed. A key finding is that the presence of acetonitrile obviates the need for using excess amounts of a more valuable terminal alkene substrates. On the basis of X-ray structure and spectroscopic investigations a rationale for the positive impact of acetonitrile is provided. Transformations leading to various E,Z-dienoates are highly Z-selective as well. Utility is highlighted by application to stereoselective synthesis of the C1-C12 fragment of biologically active natural product (-)-laulimalide.

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji-Trost coupling

The design, development and application of an efficient procedure for the concise synthesis of the 1,3-syn- and anti-tetrahydropyrimidine cores of manzacidins are reported. The intramolecular allylic substitution reaction of a readily available joint urea-type substrate enables the facile preparation of both diastereomers in high yields. The practical application of this approach is demonstrated in the efficient and modular preparation of the authentic heterocyclic cores of manzacidins, structurally unique bromopyrrole alkaloids of marine origin. Additional features of this route include the stereoselective generation of the central amine core with an appending quaternary center by an asymmetric addition of a Grignard reagent to a chiral tert-butanesulfinyl ketimine following an optimized Ellman protocol and a cross-metathesis of a challenging homoallylic urea substrate, which proceeds in good yields in the presence of an organic phosphoric acid.

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

Alkenes containing N-heteroaromatics are known to be poor partners in cross-metathesis reactions, probably due to catalyst deactivation caused by the presence of a nitrogen atom. However, some examples of ring-closing and cross-metathesis involving alkenes that incorporate N-heteroaromatics can be found in the literature. In addition, recent mechanistic studies have focused on the rationalization of nitrogen-induced catalysts deactivation. The purpose of this mini-review is to give a brief overview of successful metathesis reactions involving olefins containing N-heteroaromatics in order to delineate some guidelines for the use of these challenging substrates in metathesis reactions.

Cross-metathesis reaction of α- and β-vinyl C-glycosides with alkenes

Cross-metathesis of α- and β-vinyl C-deoxyribosides and α-vinyl C-galactoside with various terminal alkenes under different conditions was studied. The cross-metathesis of the former proceeded with good yields of the corresponding products in ClCH2CH2Cl the latter required the presence of CuI in CH2Cl2 to achieve good yields of the products. A simple method for the preparation of α- and β-vinyl C-deoxyribosides was also developed. In addition, feasibility of deprotection and further transformations were briefly explored.

Cross-metathesis of polynorbornene with polyoctenamer: a kinetic study

The cross-metathesis of polynorbornene and polyoctenamer in d-chloroform mediated by the 1(st) generation Grubbs' catalyst Cl2(PCy3)2Ru=CHPh is studied by monitoring the kinetics of carbene transformation and evolution of the dyad composition of polymer chains with in situ (1)H and ex situ (13)C NMR spectroscopy. The results are interpreted in terms of a simple kinetic two-stage model. At the first stage of the reaction all Ru-benzylidene carbenes are transformed into Ru-polyoctenamers within an hour, while the polymer molar mass is considerably decreased. The second stage actually including interpolymeric reactions proceeds much slower and takes one day or more to achieve a random copolymer of norbornene and cyclooctene. Its rate is limited by the interaction of polyoctenamer-bound carbenes with polynorbornene units, which is hampered, presumably due to steric reasons. Polynorbornene-bound carbenes are detected in very low concentrations throughout the whole process thus indicating their higher reactivity, as compared with the polyoctenamer-bound ones. Macroscopic homogeneity of the reacting media is proved by dynamic light scattering from solutions containing the polymer mixture and its components. In general, the studied process can be considered as a new way to unsaturated multiblock statistical copolymers. Their structure can be controlled by the amount of catalyst, mixture composition, and reaction time. It is remarkable that this goal can be achieved with a catalyst that is not suitable for ring-opening metathesis copolymerization of norbornene and cis-cyclooctene because of their substantially different monomer reactivities.

Facile synthesis of cyclopentenone B1- and L1-type phytoprostanes

Phytoprostanes (PhytoPs) represent non-enzymatic metabolites of α-linolenic acid (ALA), the essential omega-3 polyunsaturated fatty acid (PUFA) derived from plants. PhytoPs are present in the plant kingdom and represent endogenous mediators capable of protecting cells from oxidative stress damages in plants. Recently, it was found that such metabolites are present in cooking oil in high quantities, and also that B₁-PhytoPs protect immature neurons from oxidant injury and promote differentiation of oligodendrocyte progenitors through PPAR-γ activation. We report a novel and facile synthesis of natural 2,3-substituted cyclopentenone PhytoPs, 16-B₁-PhytoP, and 9-L₁-PhytoP. Our strategy is based on reductive alkylation at the 2-position of 1,3-cyclopentanedione using a recent protocol developed by Ramachary et al. and on a cross-coupling metathesis to access conjugate dienone system. In conclusion, this strategy permitted access to B₁- and L_1-PhytoPs in a relative short sequence process, and afford the possibility to easily develop analogs of PhytoPs.

Cross-metathesis of biosourced fatty acid derivatives: a step further toward improved reactivity

The improved catalytic conversion of bioresources, namely unsaturated fatty acid derivatives, is presented. The targeted reaction is ruthenium-catalyzed cross-metathesis with functionalized olefins (α,β-unsaturated esters), that affords shorter diesters. These can be used as biosourced (pre)monomers for the production of polyesters. It is demonstrated that switch from terminal to internal cross-metathesis partners (that is, from methyl acrylate to methyl crotonate) allows use of ppm-level catalyst loadings, while retaining high productivity and selectivity. This was exemplified on a commercial biosourced fatty acid methyl esters mixture, using minimal purification of the substrate, on a 50 g scale. We propose that this improved catalytic behavior is due to the sole presence of more stable alkylidene intermediates, as the notoriously unstable ruthenium methylidene species are not formed using an internal functionalized olefin.

Ruthenium-catalyzed intramolecular [2+2+2] cycloaddition and tandem cross-metathesis of triynes and enediynes

[2+2+2] Cycloadditions can be applied to specifically build up derivatives of benzene and cyclohexadiene and, therefore, have attracted much attention. Herein, we present an intramolecular [2+2+2] cycloaddition of triynes catalyzed by the first-generation Grubbs ruthenium complex (Ru gen-1), which can efficiently afford benzene derivatives in good yields under mild conditions. Moreover, we also report on a novel tandem cross-metathesis transformation of intramolecular enediynes also catalyzed by Ru gen-1, which has not been observed previously in related reports. On the basis of deuterium labeling experiments, a possible reaction mechanism is presented.

Ene-yne cross-metathesis with ruthenium carbene catalysts

Conjugated 1,3-dienes are important building blocks in organic and polymer chemistry. Enyne metathesis is a powerful catalytic reaction to access such structural domains. Recent advances and developments in ene–yne cross-metathesis (EYCM) leading to various compounds of interest and their intermediates, that can directly be transformed in tandem procedures, are reviewed in this article. In addition, the use of bio-resourced olefinic substrates is presented.

The cross-metathesis of methyl oleate with cis-2-butene-1,4-diyl diacetate and the influence of protecting groups

BACKGROUND

α,ω-Difunctional substrates are useful intermediates for polymer synthesis. An attractive, sustainable and selective (but as yet unused) method in the chemical industry is the oleochemical cross-metathesis with preferably symmetric functionalised substrates. The current study explores the cross-metathesis of methyl oleate (1) with cis-2-butene-1,4-diyl diacetate (2) starting from renewable resources and quite inexpensive base chemicals.

RESULTS

This cross-metathesis reaction was carried out with several phosphine and N-heterocyclic carbene ruthenium catalysts. The reaction conditions were optimised for high conversions in combination with high cross-metathesis selectivity. The influence of protecting groups present in the substrates on the necessary catalyst loading was also investigated.

CONCLUSIONS

The value-added methyl 11-acetoxyundec-9-enoate (3) and undec-2-enyl acetate (4) are accessed with nearly quantitative oleochemical conversions and high cross-metathesis selectivity under mild reaction conditions. These two cross-metathesis products can be potentially used as functional monomers for diverse sustainable polymers.

New library of aminosulfonyl-tagged Hoveyda-Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

Seven novel Hoveyda–Grubbs precatalysts bearing an aminosulfonyl function are reported. Kinetic studies indicate an activity enhancement compared to Hoveyda’s precatalyst. A selection of these catalysts was investigated with various substrates in ring-closing metathesis of dienes or enynes and cross metathesis. The results demonstrate that these catalysts show a good tolerance to various chemical functions.

Cross-metathesis of allylcarboranes with O-allylcyclodextrins

Cross-metathesis between allylcarboranes and O-allylcyclodextrins was catalyzed by Hoveyda–Grubbs 2^nd generation catalyst in toluene. The corresponding carboranyl-cyclodextrin conjugates were isolated in 15–25% yields.

Synthesis of 5'-functionalized nucleosides: S-Adenosylhomocysteine analogues with the carbon-5' and sulfur atoms replaced by a vinyl or halovinyl unit

Adenosine and uridine analogues functionalized with alkenyl or fluoroalkenyl chain at C5' were prepared employing cross-metathesis, Negishi couplings, and Wittig reactions. Metathesis of the protected 5'-deoxy-5'-methyleneadenosine or uridine analogues with six-carbon amino acids (homoallylglycines) in the presence of Grubbs catalysts gave nucleoside analogues with the C5'-C6' double bond. Alternatively, the Pd-catalyzed cross-coupling between the protected 5'-deoxy-5'-(iodomethylene) nucleosides and suitable alkylzinc bromides also provided analogues with alkenyl unit. Stereoselective Pd-catalyzed monoalkylation of 5'-(bromofluoromethylene)-5'-deoxyadenosine with alkylzinc bromides afforded adenosylhomocysteine analogues with a 6'-(fluoro)vinyl motif. The vinylic adenine nucleosides produced time-dependent inactivation of the S-adenosyl-l-homocysteine hydrolases.