Diels-Alder reaction of norbornene

Norbornene can be prepared by the Diels-Alder reaction of ethylene with dicyclopentadiene.4 It can be purchased from Matheson Coleman and Bell or the Aldrich Chemical Company, Inc. 

Diels-Alder reaction of penta-Q-acetyl-l,2-dideoxy-l-nitro-D-hept-l-enitols with cyclopentadiene afforded a mixture of 5-nitro-6 (penta-0-acetylpentitol l-yl)norbornenes the 5-exo-nitro-6-endo-(D-manno-pentitol and 5-endo-6-exo-isomers of which were characterised by X-ray diffraction analysis.  

Keywords laser-induced retro-Diels-Alder reactions of norbornene, thermal retro-Diels-Alder reactions of norbornenes and isopropylidenenorbornenes 

Because they are synthesized by Diels-Alder reaction, functionalized norbornene derivatives sold commercially consist of exo and endo isomers with the latter predominating. The drop in polymerization rate for functionalized norbornene derivatives may be ascribed to the formation of a chelate by coordination of the metal to the functionality and the C = C bond along the endo face (see Fig. 9.2). 

Homo-Diels-Alder reactions occur between norbornadiene and norbornene or unactivated alkynes giving 14 and 15a-e , respectively, by using as catalyst the cobalt complex obtained by reducing tris(acetylacetonato)cobalt with diethylaluminum chloride in the presence of bis(l, 2-diphenylphosphino)ethane."  

Cycloalkenones.3 Cycloalkenones can be prepared by a retro Diels-Alder reaction of norbornenes of type 1, conducted at 25-70° in the presence of CH3A1C12 (1 equiv.) and a reactive dienophile, usually maleic anhydride or fumaronitrile. The [4 + 2]cycloreversion was used to prepare 12-oxophytodienoic acid (4), which epi-merizes at Cu to the trans-isomer on brief exposure to acid. The precursor nor-bornene 3 was prepared from the known dienone 2 as shown. Treatment of 3 at room 

Materials. The monomers were prepared by the Diels-Alder reaction of cyclopentadlene with the corresponding vinyl and maleic compounds. The norbornene imi-des were prepared by the reaction of norbornene dicar-boxylic acid anhydride with the corresponding amines. Liquid monomers were purified by distillation under reduced nitrogen pressure and freed from residual water 

The monomer is made by the Diels-Alder reaction of dicyclopentadiene with ethylene. The catalyst for ROMP is ruthenium chloride in butanol. The process is relatively simple as the two liquids (ruthenium chloride in butanol and norbornene) are directly mixed in the extruder, in air. The norbornene to ruthenium ratio is very high (c.a. 25000) and the conversion reaches 50%. As the process operates in air, a small amount of norbornene is oxidized into epoxynorbornane (the epoxide to ruthenium ratio is c.a. 5) which can accelerate the polymerization. Indeed, mechanistic studies have shown that the catalytic reaction passes through a ruthenium hydride (formed by substitution of chlorine by butoxy ligands and further p-H abstraction) or through a ruthenium oxametallacyclobutane (formed by reaction of the ruthenium complex with epoxynorbornane) [33]. 

The Diels-Alder reaction is stereo specific. The stereochemistry of the dienophile is retained in the product i.e., cis and trans dienophiles produce different diastereoisomers in the product. For example, freshly distilled cyclopentadiene, having s-cis configuration, reacts with maleic anhydride to give c/ -norbornene-Sjh-endo-dicarboxylic anhydride. 

In the case of a cyclic conjugated diene, the Diels-Alder reaction yields a bridged bicyclic compound. A bridged bicyclic compound contains two rings that share two nonadjacent carbons. For example, cyclopentadiene reacts with ethylene to produce norbornene. 

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 

Nouguier, R, Mignon, V, Gras, J L, Synthesis of enantiomerically pure (25)-2-endo-hydroxymethyl-5-norbornene by Diels-Alder reaction based on a new fructose-derived auxiliary, J. Org. Chem., 64, 1412-1414, 1999. 

The vast majority of bicyclic phosphole derivatives with norbornene- and norbornadiene-derived skeletons are prepared via classical [4+2] cycloaddition reactions of phospholes. While Diels-Alder reactions of phospholes with CN 4 (e.g., oxides and sulfides) are common through direct reaction with dienophiles, this type of reaction is comparatively rare for CN 3 phospholes (see Section 3.15.5.1.4). 

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]. 

In the case of two different substituents at silicon, the stereochemistry of the final [4+2] cycloaddition product depends on steric repulsion. Thus, the Diels-Alder reactions of silole 51 gives mixtures of 7-sila-norbornenes 52 and of 7-sila-norbornadienes 53, respectively, where the major isomer is that in which the SiMe group is in ry -position with respect to the C(2)-C(3) double bond <2003JOM(665)196>. 

In the study of S3 sources, the interaction of the tetrathiocine 36 with norbornene yielded a mixture of the thiophene 37 and 3,4,5-trithiatricyclodecane 38 the products were derived from sulfur extrusion by the retro-Diels-Alder reaction and sulfur trapping, respectively (Equation 9) <2004JA9085>. 

Epoxide isomerization. The alcohol 3 (decahydro-2,4,7-metheno-l/T-cyclopenta[a]pentalene-3-ol) can be prepared by epoxidation of 1 (the Diels-Alder adduct of norbornene and cyclopentadiene) followed by isomerization of the resulting oxide (2) with LDA (0-35°, 48 hours). This reaction involves a transannular carbenoid insertion. 

Itoh and coworkers111 carried out tandem [2 + 2 + 2]/[4 + 2] cycloadditions catalyzed by a ruthenium catalyst. The reaction of diyne 147 with excess norbomene 148 in the presence of ruthenium catalyst 153, for example, afforded 149. Adduct 150 either dissociated from the catalyst or reacted with another equivalent of norbornene. In the latter case, a ruthenium catalyzed Diels-Alder reaction occurred, affording hexacyclic adduct 152 via 151 (equation 43). Compounds 150 and 152 were obtained in yields of 78% and 10%, respectively. Both cycloaddition reactions proceeded with complete stereoselectivity. When 1,6-heptadiyne was used instead of 147, only trace amounts of a cycloadduct were obtained. Replacing norbornene by norbornadiene, which was expected to result in polymer formation, did not afford any adduct at all. 

An alternative synthesis of a thermally stable cyclopentadienyl functionalized polymer involved ring bromination of poly(oxy-2,6-diphenyl-l,4-phenylene), followed by lithiation with butyl lithium to produce an aryllithium polymer. Arylation of 2-norbornen-7-one with the metalated polymer yielded the corresponding 2-norbornen-7-ol derivative. Conversion of the 7-ol to 7-chloro followed by treatment with butyl lithium generated the benzyl anion which undergoes a retro Diels-Alder reaction with the evolution of ethylene to produce the desired aryl cyclopentadiene polymer, 6. 

This group has used the same reaction conditions with diynes 182 and cyclic dienes like cyclopentadiene to form tetracyclic enone 183 which was transformed into triquinane 184 by means of an oxidative cleavage of the double bond. When phenyl groups at the alkyne terminus were substituted by H or Me they observed a competitive [2 + 2 + 1]/[2+ 2 + 2] process, with the participation of two diyne molecules giving compounds 185 (Scheme 54) [171]. No mechanistic hypothesis appears in this work but the formation of a norbornene derivative by means of the Diels-Alder reaction of cyclopentadiene and the diyne that would react with the other triple bond of the diyne seems attractive in this case. 

Some thermosets are made with maleic anhydride only, or with other unsaturated 1,2-dicarboxylic acids or anhydrides such as itaconic acid or methylenesuccinic acid [7], chlorendic acid or 1,4.5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic acid (or anhydride), 1,4.5,6,7-pentachloro-5-norbornene-2,3-dicarboxylic acid anhydride or 1,4.5,6-tetrachloro-5-norbornene-2,3-dicarboxylic acid anhydride. These norbomene derivatives can be obtained from the Diels-Alder condensation of the chlorinated cyclopenta-1,3-dienes and maleic anhydride, as shown in the following reaction  

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