Norbornadiene-cyclopentadiene

The reaction has wide scope in respect of the dienophUe / -substituent. The representative less reactive dienophiles, crotonoyl- and cinnamoyl-oxazolidinone, react with cyclopentadiene at -15 °C and 25 °C for 20 h and 24 h giving cycloadducts in 99% ee and 96% ee, respectively. The 3-chloropropenoyl derivative also affords the adduct in high optical purity (96% ee) this adduct is transformed to 2-(methoxycar-bonyl)norbornadiene, a useful chiral building block. Thus, the 3-chloropropenoyl derivative can be regarded as a synthetic equivalent of an acetylene dienophile. 

Norbornadiene (Problem 14.41) can be prepared by reaction of chloroethyl-ene with 1,3-cyclopentadiene, followed by treatment of the product with sodium ethoxide. Write the overall scheme, and identify the two kinds of reactions. 

Norbornadienes, norbornenones and their homologs have been prepared [23, 24] by cycloaddition of cyclopentadiene (21) and cyclohexadiene (22) with l-benzenesulfonyl-2-trimethylsilylacetylene (23) and l-ethoxy-2-carbomethox-yacetylene (24). Both were efficient dienophiles in the cycloaddition processes and dienophile 23 acted as an effective acetylene equivalent (Scheme 2.12). Norbornanes and their homologs can also be attained by Diels-Alder reaction... 

Edman and Simmons [146] synthesized bicyclo[2.2.1]hepta-2,5-diene-2,3-dicar-boxylic anhydride 80 as a facially perturbed dienophile on the basis of the norbornadiene motif, and its top selectivity in Diels-Alder reactions with cyclopentadiene (top-exo top-endo = 60 70 1) was observed by Bartlett (Fig. 14) [147], The most preferred addition was top-exo addition, along with the minor addition modes, top-endo bottom-enrfo addition (Fig. 14). The addition of butadiene to this anhydride preferentially afforded the top-adduct (top bottom = 6 1). In the addition of anthracene, a top-adduct was formed exclusively. 

Cycloaddition of bicyclo[2.2.1]hept-2-ene-2,3-dicarboxylic anhydride 81 with cyclopentadiene was also studied by Bartlett et al., who found exclusive top addition, the top-endo/top-exo ratio being 3 2 [147]. The endolexo ratio is significantly different from that of 80 (60-70 1). The observed top selectivity in norbornadiene (80) and norbomene (81) derivatives is consistent with the inherent top reactivity of norbomanone 25 and norbomene 57. Orbital unsymmetrization of the dienophile... 

A convenient synthetic method for 1,2,3-triazoles unsubstituted at C-4 and C-5 utilizes a reaction of azides with norbornadiene, for example, Scheme 29 <2004JOC1081>. The process is performed in refluxing dioxane. In the first step, norbornadiene undergoes 1,3-dipolar cycloaddition to glucose-derived azide 225 to give triazoline 226. The following retro Diels-Alder reaction results in the elimination of cyclopentadiene to furnish triazole derivative 227 in 79% yield. 

Diethyl azidomethanephosphonate 228 reacts with norbornadiene at room temperature to give triazoline 229 in 86% yield. When heated at 60°C, derivative 229 decomposes with elimination of cyclopentadiene to provide (1,2,3-triazol-l-yl)methanephosphonate 230 in 74% yield. However, when it is left at room temperature for an extended period of time, triazoline 229 undergoes slow conversion to aziridine 231 with elimination of nitrogen (Scheme 30)... 

In 1991, Park reported123 the first synthesis of iron alkynylcarbene complexes (184), involving the nucleophilic attack of a lithium acetylide on pentacarbonyl iron, followed by electrophilic quench. With such compounds in hand, he proceeded to investigate their reactivity123,124 and found that upon addition of cyclopentadiene to the alkynylcarbene complexes 184, the products formed were 774-vinylketene complexes (185). During column chromatography, some of these products (185.a and 185.b) were transformed into the tricarbonyl(norbornadiene)iron derivatives 186. Others (185.C and 185.d, not shown) were hydrolyzed as part of the workup procedure, to afford pure samples of the norbornadiene complexes 186.C and... 

Of the cyclic olefins, norbornadiene replaces two CO groups from one Co to yield a labile complex 159, 160, 235), cyclooctatetraene replaces the axial CO ligands from all three cobalt atoms 53) and is itself replaced by other Lewis bases 330), and cyclopentadiene forms the unusual complex [95] with Co3(CO)gCMe 159,160). A few catalytic reactions were observed with methinyltricobalt enneacarbonyls including the dimerization of norbornadiene 160, 235) and the polymerization of functional olefins 312) with different Co3(CO)9CX. 

Reaction of (325) with norbornadiene affords 2,3,6-trifluoropyridine (376a), the formation of which is explained by elimination of cyclopentadiene from the dihydropyridine... 

There are several cases of polycyclic triazolines, obtained by azide addition to the strained olefinic bond in bi- and tricyclic systems, that are susceptible to retro Diels-Alder reaction to yield 1-substituted triazoles. A well-established example is the monoadduct from norbornadiene and phenyl azide, which decomposes at 90-100°C to give 1-phenyltriazole and a cyclopentadiene (Scheme 138).2s 97—" 1 47 430 Similarly, the cycloadduct from the reaction of 7-oxabenzonorbornadiene and 1-azidoadamantane, when heated at 110°C, affords good yields of l-(l-adamantyl)-l,2,3-triazole in a retro Diels-Alder reaction.155... 

DMB CHD 2,3-dimethylbuta-l,3-diene MBD cyclohexadiene NBD norbornadiene. 2-methylbuta-1,3-diene BD buta-1,3-diene Cp cyclopentadiene ... 

A new synthesis of isoxazoles is by successive treatment of a ketoxime with butyllithi-um, the ester of a carboxylic acid and sulfuric acid, e.g. 1 -> 2 (94S989). Hitrovinyl oximes 3 (R1, R3 = alkyl or aryl) undergo oxidative cyclization to isoxazoles 4 by the action of DDQ or iodine/potassium iodide (94JHC861). Flash-vacuum pyrolysis of the 1,3-dipolar cycloadduct 5 of acrylonitrile oxide to norbornadiene results in a retro-Diels-Alder reaction to give cyclopentadiene and 3-vinylisoxazole 6 (94CC2661). 

If the dienophile (norbornadiene) is chlorinated instead, either via the reaction of hex with vinyl chloride followed by dehydrochlorination, or directly with acetylene, to give 1,2,3i4, 7 7-hexachlorobicyclo( 2.2.1 J] hepta-2,5-diene (hexachloronorborn-adiene B, Figure 3)i this compound reacts with cyclopentadiene to give isodrin (C precursor of the epoxide, endrin) having the opposite (endo-,endo-) stereochemistry to aldrin (and dieldrin), respectively (12). Isodrin has not found commercial use but endrin has been widely used in tropical and sub-tropical agriculture - to control cotton pests, for example. 

They noted that in dimethoxyethane or in iso-octane (path a), the major product was dicarbonylcyclopentadienylcobalt (2) which must arise as a result of a retro Diels-Alder reaction of the norbornadiene (which would lead to the formation of acetylene and cyclopentadiene). When the solvent was changed to an aromatic hydrocarbon such as benzene or toluene (path b), the major cobalt-containing product was shown to be a complex derived from Co4(CO)i2, with three CO ligands on an apical cobalt being replaced by a molecule of the aromatic solvent (3). The group noted that they were also obtaining hydrocarbon and ketonic products derived from norbornadiene, acetylene and carbon monoxide .1,2... 

The 1,4-diphospha-l,3-butadienes are suitable as ligands for cr-coordi-nated complexes with transition metals. Attempts to carry out pericy-clic reactions with maleinic anhydride, acetylene dicarboxylate esters, dimethylbutadiene, or cyclopentadiene failed, but Diels-Alder reactions with norbornadienes were successful (94). Earlier attempts to synthesize 1,4-diphosphabuta-l,3-dienes with oxalychloride and phenyl-bis(silyl)phosphane proceeded via ring closure [Eq. (42)] (89), where R = Ph (a) or [Pg.285]

Benzo[ ]furan-based azide was also reported to undergo a 1,3-dipolar cycloaddition with norbornadiene as dipolar-ophile to give a triazole after extrusion of cyclopentadiene (Equation 180) <2001T7729>. 

Aldrin, a chlorinated insecticide now banned for use in the United States, can be made by Diels-Alder reaction of hexachloro-l,3-cyclopentadiene with norbornadiene. What is the structure of aldrin ... 

An interesting finding is the predominant formation of syn-isomers by monocyclo-propanation of cyclopentadienes 67b). This is what one would expect when carbenes or carbenoids are involved 63). Also one isomer is found in the codimerization of 1-propyl-cyclopropene-3-carboxylate (77) with norbornadiene (Eq. 14). 

With methyl 2-alkylcycloprop-2-enecarboxylates, on the other hand, only [2-1-1] cycloaddition to the tricyclic dimers of cyclopentadiene (18) occurs. Only the strained double bond in the norbornene substructure is cyclopropanated, and the exo-adducts are formed. The Z/E isomeric ratios (6 1 and 2.5 1) are comparable to the ratios obtained in the reactions with norbornadiene vide supra). A mechanism proposing ring opening of the cyclopropene and attack on the metal-coordinated alkene in a concerted way has been suggested in order to explain the stereoselectivity of the reaction. ... 

Norbornadiene, (which is the preferred name for bicyclo[2.2.1]hepta-diene-2,5 (I), was first reported in the patent literature in 1951 (5). It is commercially available (e.g., from Matheson, Coleman and Bell) and usually manufactured from the reaction of acetylene with cyclopentadiene under pressure at temperatures between 230° and 320°. It may... 

The metal-catalyzed dimerization of norbornadiene was discovered in 1961 by two independent groups of workers (3, 4) and since then has received considerable attention by others. The various possible dimers are shown in Table II. Excluding structures in which the cyclobutane ring is fused, trans, 14 dimers (XXIII-XXXVI) are possible, of which seven have been isolated. The structures of six are now rather well established. Initially (3) the structure of one dimer was considered to be (XXXVII). In the meantime NMR measurements (44) and synthetic studies (45, 46) have shown that (XXXVII) is (XXV), the liquid exo-trans-endo dimer. Pyrolysis of both (XXV) and (XXIII) (m.p. 67-68°) yields cyclopentadiene and a mixture of bicyclo[4.2.1]nona-2,4,7-triene (XXXVIII) and exo-tricyclo[4.2.1.02 ]nona-3.7-diene (XXXIX) (46). The exo-trans-endo isomer (XXV) decomposes more... 

In an analogous reaction of (2) with norbornadiene, the tetracyclic adduct (116) is formed which on heating undergoes a retro Diels-Alder reaction with formation of the thiophene derivative (117). Further cycloaddition reactions of mesoionic 1,3-dithiolones have been carried out with cyclopentadiene, 1,3-cyclohexadiene and 1,5-cyclooctadiene (78CB3037). 

---