Norbornene derivatives

Optically active norbornene derivatives [26] have been prepared by cycloaddition of hexachlorocyclopentadiene with /-menthylacrylate and /-menthylallyl-ether (Equation 2.9). Low levels of enantiomeric excess have been obtained in the thermal processes, whereas Lewis acid catalyzed reactions (BF3, BBr3, AICI3, SnCU, DCM, 40-80 °C) gave better results. 

Phosphonoformic acid (85) decarboxylated in acid solution, and it was proposed that the uncatalysed reaction involved a simple decarboxylation of the zwitterion. The acid-catalysed reaction showed some kinetic similarity to that of mesitoic acid and an elimination of carbon dioxide as trihydroxymethylcarbonium ion was preferred. Participation of the trans vicinal phosphonyl group in the solvolysis of the halides (86) and (87) has been deduced from rate measurements. In the norbornene derivatives, the relative rates of loss of chloride from (87a) and (87b) were 5 x 10 1. 

To date, only double Heck reactions have been described, but triple Heck reactions are also possible [39]. Reaction of the alkynyl aryl iodide 6/1-55 with norbor-nene in the presence of Pd(OAc)2, triphenylphosphane and triethylamine as base led to the cyclopropanated norbornene derivate 6/1-59 as a single diastereomer in 40% yield (Scheme 6/1.13). It can be assumed that the alkenyl Pd-species 6/1-56 is first formed stereoselectively, and this undergoes a Heck reaction with norbornene... 

A carbazole-functionalized norbornene derivative, 5-CN-carbazoyl methy-lene)-2-norbornene, CbzNB, was polymerized via ROMP using the ruthenium catalyst Cl2Ru(CHPh)[P(C6Hii)3]2 [100]. The polymerization was conducted in CH2C12 at room temperature, to afford products with polydispersity indices close to 1.3. Subsequent addition of 5-[(trimethylsiloxy)methylene]-2-norbornene showed a clear shift of the SEC trace of the initial polymer, indicating that a diblock copolymer was efficiently prepared in high yield. 

Synthesis of block copolymers of norbornene derivatives, with different side groups, has been reported via ROMP [101]. Initially, exo-N-bulyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide was polymerized in acetone at room temperature with a ruthenium initiator (Scheme 40). The conversion of the reaction was quantitative. Subsequent addition of norbornene derivative carrying a ruthenium complex led to the formation of block copolymers in 85% yield. Due to the presence of ruthenium SEC experiments could not be performed. Therefore, it was not possible to determine the molecular weight... 

The living character of the ROMP promoted by the initiator Ru(CHPh)(Cl)2 (PCy3)2 (Cy = cyclohexane) was tested with the synthesis of diblock, triblock, and tetrablock copolymers of norbornene derivatives carrying acetyl-protected glucose, [2,3,4,6-tetra-O-acetyl-glucos-l-O-yl 5-norbornene-2-carboxylate], A or maltose groups, [2,3,6,2/,3/,4/,6/-hepta-0-acetyl-maltos-1-O-yl 5-norbornene-2-carboxylate], B, shown in Scheme 41 [102]. The AB, ABA, and ABAB structures were prepared by sequential addition of monomers with narrow molecular weight distributions to quantitative conversions. 

Attempts to expand the range of substrates to include cyclopropenes20 and norbornene-derived meso-bicyclic hydrazines25 have recently been reported. A further noteworthy contribution has been the development of a recyclable hydroboration process by the group of Fernandez26-28 These and other approaches toward... 

Successful ring-opening cross-metathesis with symmetrical internal acyclic alkenes was, however, achieved by Blechert and Schneider [49]. Reaction of a variety of functionalised norbornene derivatives with fraws-hex-3-ene in the presence of the ruthenium vinylalkylidene catalyst 4 yielded the ring-opened products as predominantly trans-trans isomers (for example Eq. 33). 

Fig. 14. A,B. A living polymerization of mannose-substituted norbornene derivatives can be used to produce materials of defined lengths for biological testing. B The relationship between polymer length and biological activity was explored...

On the contrary, if a highly strained cyclic olefm such as the cyclopropene 16 [20] or the norbornene derivative 17 [21] is employed, the titanacycle is cleaved to form the corresponding titanocene-alkylidene 18 or 19. This reaction is clearly enhanced by the concomitant release of intrinsic strain energy (Scheme 14.10). 

Short PS macromonmers (DP = 4 or 9) polymerized completely under ROMP conditions. Macromonomers with DP = 14 to 46 invariably led to incomplete polymerization, suggesting that the dense polymacromonomer imposes steric limitations on the polymerization. Heroguez et al. studied the ROMP of polyethylene oxide) macromonomers [111, 112], The macromonomers are prepared from a norbornene derivative according to the following sequence ... 

In contrast to the above-mentioned cydoadditions, normal electron demand Diels-Alder reactions exclusively form products where the terminal C=C bond of the allene was attacked by the diene. For example, cydoaddition of N-allenylsulfeni-mide 281 with cydopentadiene (282) affords norbornene derivative 283 (Eq. 8.37) [148]. 

The norbornene derivative 16, obtained exclusively as the exo adduct via a Diels-Alder reaction of itaconic anhydride with cyclopentadiene followed by hydrolysis and esterification [7], was found to be a suitable precursor for an enolate of type 14 (Scheme 2). Due to the quaternary center at C-3 eno-lization with base proceeded unambiguously, giving rise to a diastereomeric mixture of lactones 17/18 after reaction with hexanal. Retro-Diels-Alder reaction led to the monocyclic lactones 19/20 (2 1), elegantly unmasking the cxo-methylene group found in so many paraconic acids [8]. Hydrolysis of this mixture in refluxing butanone with 6 N HCl [9] effected epimerization... 

North and Banti observed double-ring-opening metathesis of dialkynylcycloalkenes and obtained a tricyclic compound from a norbornene derivative shown in Equation (16)." " ... 

Certain norbornene derivatives, for example, 5-(2-naphthalene-carbonyloxy)bicyclo[2.2.1 ]hept-2-ene or 5-(4-biphenylcarbonyloxy)-bicyclo[2.2.1]hept-2-ene produce a polymer that is effective in producing molded products with excellent transparency, low water absorption, and low birefringence (29). 

The norbornene derivative is polymerized by a ring opening metathesis polymerization, followed by a hydrogenation reaction. The polymers can be used for optical disks, optical lenses, and optical films or sheets. 

Multi-component catalyst systems based on palladium compounds and phosphorus compounds show a particularly high activity (35). The high catalytic activity is not deteriorated in the course of polymerization. Substituted norbornene derivates can be used that are otherwise difficult to polymerize. 

Chloromethyl polystyrene can be converted to a free-radical initiator by reaction with 2,2,6,6-tetramethylpipcridinc-/V-oxyl (TEMPO). Radical polymerization of various substituted alkenes on this resin has been used to prepare new types of polystyrene-based supports [123]. Alternatively, cross-linked vinyl polystyrene can be copolymerized with functionalized norbornene derivatives by ruthenium-mediated ringopening metathesis polymerization [124],... 

A few examples are available in which regiocontrol in the cyclopropanation of non-conjugated diene is catalyst-dependent. An early example is showed in equation 118. Copper(II) triflate catalysed cyclopropanation of diene 132 with diazomethane occurs preferentially at the less substituted double bond, whereas copper(II) acetylacetonate in contrast promotes cyclopropanation at the more substituted double bond (equation 118)13. Regiocontrol in the cyclopropanation of norbornene derivative 133 is strongly catalyst-dependent (equation 119). When diphenyldiazomethane is used as carbenoid precursor, the regioselectivity of this cyclopropanation is significantly enhanced165. 

Photocyclization, arising by intramolecular hydroxyl addition to a carbon-carbon double bond, occurs in the norbornene derivatives (489) and yields the cyclic ethers (490).428 This is in marked contrast to the inter-... 

TT-Aryl participation in bromination of a norbornene derivative has been reported (194 — 280). Acid opening of the corresponding exo-epoxide proceeds in a similar way402. 

When catalysts of the type 10/GaBr3 are used to initiate the ROMP of norbornene derivatives at low temperature (—50 °C) the intermediate transoid metallacyclobutane complexes (the precursors to the formation of trans double bonds) may be observed. The corresponding cisoid complexes are not stable enough to be detected. No metallacyclobutane complexes are observed in the absence of GaBr3100 112-114. 

Strained cyclohexenes, such as norbornene derivatives, can undergo retro-Diels-Alder reactions even at relatively low temperatures, and this reaction can be used to prepare 1,3-dienes and alkenes (e.g. synthesis of cyclopentadiene by thermolysis of... 

Facile, regioselective ring opening-cross-metathesis reactions between unsymmet-rical norbornene derivatives and electron-rich alkenes in the presence of the second-generation Grubbs catalyst have been reported to generate highly substituted furans and pyrroles.114... 

Scheme 5.6 CuOTf-catalyzed [2 + 2] photocycloaddition used for a topology study of inter and intramolecular dimerization of a norbornene derivates.

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