2-Norbomene

Far more is achieved by and TM 289 is simply synthesised by irradiating norbomene (A). The stereochemistry turns out all right. How about TM 290 ... 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Diels-Alder Reactions. The important dimerization between 1,3-dienes and a wide variety of dienoplules to produce cyclohexene derivatives was discovered in 1928 by Otto Diels and Kurt Alder. In 1950 they won the Nobel prize for their pioneering work. Butadiene has to be in the j -cis form in order to participate in these concerted reactions. Typical examples of reaction products from the reaction between butadiene and maleic anhydride (1), or cyclopentadiene (2), or itself (3), are <7 -1,2,3,6-tetrahydrophthaHc anhydride [27813-21 -4] 5-vinyl-2-norbomene [3048-64-4], and 4-vinyl-1-cyclohexene [100-40-3], respectively. 

Ring-Opening Metathesis Polymerization. Several new titanacyclobutanes have been shown to initiate living ring-opening metathesis polymerization (ROMP) systems. These have been used to make diblock and triblock copolymers of norbomene [498-66-8] (N) and its derivatives (eg, dicyclopentadiene [77-73-6] (D)) (Fig. 2) (41). 

The idea of using polyunsaturated monomers is rooted in the eady history of acryUc elastomers. The first monomers used were butadiene [106-99-0] (35), isoprene [78-79-5] (36), and aHyl maleate [999-21-3] (37), but they did not find commercial success because during polymerization large portions of polymer were cross-linked. Other monomers have been proposed more recentiy tetrahydrobenzyl acrylate (38), dicyclopentenyl acrylate [2542-30-2] (39), and 5-ethyhdene-2-norbomene [16219-75-3] (40). The market potential, at least for the more recent ones, is stiU to be determined. 

The most commonly used third monomer is 5-ethyHdene-2-norbomene [16219-75-3] or ENB ... 

Lipase-catalyzed enantioselective transesterification of 0-substituted-l,2-diols is another practical route for the synthesis of P-blockers. Lipase PS suspended in toluene catalyzes the transesterification of (63) with vinyl acetate to give the (5)-ester in 43% yield and >98% ee (78). The desired product, optically pure (R)-ttitylglycidol, is then easily obtained by treating the ester with alcohoHc alkaU. Moreover, Pseudomonas Hpase catalyzes the acylation of oxazohdinone (64) with acetic anhydride in very good yield and selectivity (74). PPL-catalyzed transesterification of a number of /n j -norbomene derivatives proceeds in about 30% yield and 92% ee (79,80). 

Ethylene-cyclo-olefin copolymers have been known since 1954 (DuPont USP2 721 189) but these materials only became of importance in the late 1990s with the development of copolymers of ethylene and 2-norbomene by Hoechst and Mitsui using metallocene technology developed by Hoechst. The product is marketed as Topas by Ticona. By adjustment of the monomer ratios polymers with a wide range of Tg values may be obtained including materials that are of potential interest as thermoplastic elastomers. This section considers only thermoplastic materials, cyclo-olefins of interest as elastomers are considered further in Section 11.10. 

The Ticona materials are prepared by continuous polymerisation in solution using metallocene catalysts and a co-catalyst. The ethylene is dissolved in a solvent which may be the comonomer 2-norbomene itself or another hydrocarbon solvent. The comonomer ratio in the reactor is kept constant by continuous feeding of both monomers. After polymerisation the catalyst is deactivated and separated to give polymers of a low residual ash content and the filtration is followed by several degassing steps with monomers and solvents being recycled. 

Thermoplastics grades have a norbomene content in the range 60-80% with Tg values from 60-180°C, in this range the glass transition being almost linearly related to the norbomene content. The modulus of elasticity increases with norbomene content and for commercial materials is in the range 2600-3200 MPa but density (1.02g/cm), tensile strength 66 MPa and water absorption (<0.01 %) is little affected by the monomer ratio. 

The dienes used are such that the double bonds in the polymer are either on a side chain or as part of a ring in the main chain. Hence should the double bond become broken the main chain will remain substantially intact. Dienes commonly used include dicyclopentadiene, ethylidene-norbomene and hexa-1,4-diene Table 11.17). 

Substituted and unsubstituted bi- or multi-cyclic mono-, di- or multi-olefins, i.e. containing condensed rings at least one of which contains a double bond. Norbomene is homopolymerised commercially whilst, as previously mentioned, ethylidenenorbomene and dicyclopentadiene are used as the cure site monomer in EPDM rubbers. 

The monomer, norbomene (or bicyclo[2.2.l]hept-2-ene), is produced by the Diels-Alder addition of ethylene to cyclopentadiene. The monomer is polymerised by a ring-opening mechanism to give a linear polymer with a repeat unit containing both an in-chain five-membered ring and a double bond. Both cis-and trans- structures are obtainable according to the choice of catalyst used ... 

Ethylene-norbomene copolymers of interest as thermoplastics were discussed in Section 11.6.2. It is however to be noted that copolymers with a norbomene content of about 30 wt% have a glass transition temperature of about 0°C and that copolymers with norbomene contents up to this amount are being evaluated as thermoplastic elastomers... 

The stereoselective reactions in Scheme 2.10 include one example that is completely stereoselective (entry 3), one that is highly stereoselective (entry 6), and others in which the stereoselectivity is modest to low (entries 1,2,4, 5, and 7). The addition of formic acid to norbomene (entry 3) produces only the exo ester. Reduction of 4-r-butylcyclohexanone (entry 6) is typical of the reduction of unhindered cyclohexanones in that the major diastereomer produced has an equatorial hydroxyl group. Certain other reducing agents, particularly sterically bulky ones, exhibit the opposite stereoselectivity and favor the formation of the diastereomer having an axial hydroxyl groi. The alkylation of 4-t-butylpiperidine with benzyl chloride (entry 7) provides only a slight excess of one diastereomer over the other. 

The preference for endo attack in 7,7-dimethylnorbomene is certainly steric in origin, with the 7-methyl substituent shielding the exo direction of approach. The origin of the preferred exo-attack in norbomene is more subject to discussion. A purely steric explanation views the endo hydrogens at C—5 and C—6 as sterically shieldihg the endo approach. There probably is also a major torsional effect Comparison of the exo and endo modes of reproach shows that greater torsional strain develops in the endo mode of... 

The reaction course taken by photoexcited cycloalkenes in hydroxylic solvents depends on ring size. 1-Methylcyclohexene, 1-methylcycloheptene, and 1-methylcyclooc-tene all add methanol, but neither 1-methylcyclopentene nor norbomene does so. The key intermediate in the addition reactions is believed to be the highly reactive -isomer of the cycloalkene. 

Table 2. Products of Addition of Halogen Fluorides to Norbomene...

The [S3N3]" cation is of interest as an example of an antiaromatic eight TT-electron system (Section 4.4). Ab initio molecular orbital calculations indicate that a triplet cation, with a planar ring, is more stable than the singlet cation. The [S3N3]" cation has been obtained as the norbomene adduct 5.16, but salts of the free cation have not been isolated. ... 

We will apply these results to data on the addition of m-nitrophenylazide to norbomene in ethyl acetate ... 

Direct conversion of an Fmoc group to a Cbz group KF, TEA, DMF, A-benzyloxycarbonyloxy-5-norbomene-2,3-dicarboximide, 7-12 h, 83-99% yield. ... 

Stereochemical aspects of epoxidation of substituted norbomenes and accompanying intramolecular transformations 98UK299. 

Abbreviations aapy, 2-acetamidopyridine Aik, alkyl AN, acetoniuile Ar, aryl Bu, butyl cod, 1,5-cyclooctadiene COE, cyclooctene COT, cyclooctatetraene Cp, cyclopentadienyl Cp , penta-methylcyclopentadienyl Cy, cyclohexyl DME, 1,2-dimethoxyethane DME, dimethylformamide DMSO, dimethyl sulfoxide dmpe, dimethylphosphinoethane dppe, diphenylphosphinoethane dppm, diphenylphosphinomethane dppp, diphenylphosphinopropane Et, ethyl Ec, feirocenyl ind, inda-zolyl Me, methyl Mes, mesitylene nb, norbomene orbicyclo[2.2.1]heptene nbd, 2,5-norbomadiene OTf, uiflate Ph, phenyl PPN, bis(triphenylphosphoranylidene)ammonium Pi , propyl py, pyridine pz, pyrazolate pz, substituted pyi azolate pz , 3,5-dimethylpyrazolate quin, quinolin-8-olate solv, solvent tfb, teti afluorobenzobaiTelene THE, tetrahydrofuran THT, tetrahydrothiophene tmeda, teti amethylethylenediamine Tol, tolyl Tp, HB(C3H3N2)3 Tp , HB(3,5-Me2C3HN2)3 Tp, substituted hydrotiis(pyrazol-l-yl)borate Ts, tosyl tz, 1,2,4-triazolate Vin, vinyl. 

A somewhat more complex application of this notion is represented by the CNS stimulant fencamfine (83). Diels-Alder addition of cyclopentadiene and nitrostyrene affords the norbomene derivative, 80. Catalytic hydrogenation reduces both the remaining double bond and the nitro group (81). ° Condensation with acetaldehyde gives the corresponding imine (82) a second reduction step completes the synthesis of fencamfine (83). ... 

The precise control of ROMP methodology has been exploited by Schrock and co-workers in the polymerization of a norbomene monomer functionalized with a distyrylbenzene side-chain 70 [1051. When calcium is used as a cathode, an internal device efficiency of 0.3% is observed and the peak emission is in the blue (475 nm). 

Hydantoin, condensation with -hy-droxybenzaldehyde, 43,49 Hydration of norbomene by formic add, 43, 79... 

New kinds of living polymer systems result from the reactions of transition metals with cyclic, strained olefins 16). These polymerizations proceed through the intermediacy of metal carbenes and are exemplified by the polymerization of norbomene initiated by bis(cyclopentadienyl)-titane-cyclobutane described recently by Grubbs17>. 

By the addition of organotin hydrides to norbomene and norboma-diene, and subsequent reactions of the products, a variety of nor-bomyl-, norbornenyl-, and nortricyclyl-tin compounds has been isolated, and identified (67-69). 

In anti addition to a cyclic substrate, the initial attack by the electrophile is also from the less-hindered face. However, many (though not all) electrophilic additions to norbomene and similar strained bicycloalkenes are syn additions." In these cases attack is always from the exo side, for example," ... 

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