Diels-Alder reactions of norbornadienes

Table 1.4 Ni(COD)2/PPh3 catalyzed Aomo-Diels-Alder reaction of norbornadiene with electron-deficient dienophiles...

This route provides a convenient method for synthesizing deltacyclenes 89 which have been proven to be useful in the synthesis of highly strained unnatural products of theoretical interest [88]. Diels-Alder reactions of norbornadiene (88) have been successfully activated by a nickel catalyst [89] (Scheme 3.17). Amarked influence of the catalyst on the endo-exo diastereoselectivity has been observed. 

Keywords homo-Diels-Alder reaction of norbornadiene... 

Brunner H. Enantioselective Catalysis With Transition Metal Componnds. Right or Left - This Is the Qnestion Adv. Chem. Ser. 1992 230 143-152 Keywords homo-Diels-Alder reaction of norbornadiene... 

The most efficient catalysts for the homo Diels-Alder reactions of norbornadiene were found to be cobalt327 and nickel328 complexes. The general mechanistic pathway that has been proposed for these reactions has been depicted in equation 161329. According to this mechanism, co-ordination of norbornadiene and the olefin or acetylene to the metal center gives 557, which is in equilibrium with metallocyclopentane complex 558. Then, insertion of the olefin or acetylene in the metal-carbon bond takes place to form 559. Reductive elimination finally liberates the deltacyclane species. 

The homo-Diels-Alder reactions of norbornadiene with dimethylacetylene dicarboxylate (DMAD) and TCNE are reported to have activation volumes of about - 30 cm3 cm-1 and classical examples have already been reviewed [10]. 

Gugelchuk, M. M., Wisner, J. Density Functional Study of Intermediates in the Nickel-Catalyzed Homo-Diels-Alder Reaction of Norbornadiene with Alkenes. Organometallics 995, 14,1834-1839. 

The homo-Diels-Alder reactions of norbornadiene and quadricyclane with acrylic esters in the presence of nickel catalysts and phosphorus ligands gives, with different kinetics, the same endojexo mixtures of adducts, leading to the conclusion that a common intermediate and stepwise mechanism are involved.A systematic investigation of the effects of several phosphorus ligands on the stereoselectivity of the nickel-catalyzed homo-Diels-Alder reaction of norbornadiene with acrylonitrile shows a clear correlation between ligand bulk and the ratio of exoj endo-Komers ... 

Applications of transition metal catalyzed cyclooligomerizations and cocyclooligomerizations to stereoselective synthesis are restricted to some special methods, such as cyclotrimerizations and cocyclotrimerizations of alkenes and alkynes ([2 + 2 + 2] cyclooligomerizations), as well as homo-Diels-Alder reactions of norbornadiene (formal [2 -b 2 + 2] cyclooligomerizations). 

Homo-Diels-Alder reactions of norbornadiene. In the presence of Ni(COD)2 and P(C6H5).i (1 2) norbornadicnes can react with activated alkencs at 80° to give [2 + 2 + 2] adducts. Preliminary studies of the rcgiosclectivity indicate that this homo-Diels-Aldcr reaction can be useful for synthesis of complex molecules. Thus reaction of methyl norbornadiene-2-carboxylatc with acrylonitrile results in only two... 

Cobalt(II) iodide-triphenylphosphine-zinc systems catalyse the homo-Diels-Alder reaction of norbornadiene with alkynes R C=CR (R = Bu, Ph or SiMe3 R = H, Me or Et) to give the tetracyclic adducts 512. Asymmetric induction has been reported for the cobalt acetylacetonate-catalysed homo-Diels-Alder addition of 1 -hexyne to norbornadiene in the presence of the diphosphine (R)-(+)-Ph2PCH2CHMePPh2 to yield the dextrorotatory product 513 in 78% enantiomeric excess. Six new stereocentres are created in this... 

HC(17)1, p. 53), and by retro-Diels-Alder reaction of the adduct from norbornadiene and fulminic acid <67AG(E)456). 

Bistrifluoromethyl-l,3,4-thiadiazole 71 undergoes a Diels-Alder reaction with norbornadiene under high pressure to give the unstable cycloadduct 72 which rapidly loses dinitrogen forming the 1,3-dipolar intermediate 73. The [4+2] cycloaddition of the intermediate 73 with a second alkene affords product 74 in 29% yield (Scheme 5) <1997SL196>. 

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 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 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>. 

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

An investigation of the homo-Diels-Alder reaction between norbornadiene and different dienophiles showed general endo selectivity in the products 1 for R = H however, when... 

The latter reaction is homologous to the well-known homo-Diels-Alder reaction of dienophiles with norbornadiene. ° Both reaction types proceed via dipolar intermediates. 

Diels-Alder reaction of l,l-dimethylcyclopenta-2,4-diene and 2-acetoxy-acrylic acid ester gives two esters (290), which can be converted by conventional reductive steps into the two a-fenchene hydrates (291) and (292). Cyclopen-tadiene and ethyl but-2-ynoate also undergo a Diels-Alder reaction, this time to a norbornadiene ester (293), which was the start of a synthesis of a Cu aldehyde (294) found in East Indian sandalwood oil. ... 

Diels-Alder reaction of methyl lO-oxodec-0-ynoate and cyclo-pentadiene gave the norbornadiene (233). From this compound the... 

Diels-Alder reactions of the o-quinodimethanes (167) and (168) with cyclopentene, cJ5-but-2-ene, norbornadiene, and benzonorbornadiene gave mainly endo-adducts similar behaviour was noted for benzo[c]furan except that the exo-adduct predominated for addition to norbornadiene. " Since it is thought that steric effects for endo- or exo-addition to (167) and (168) are similar, an attractive interaction between endo-alkyl groups and the diene systems is proposed to explain the predominant endo-addition pathway. In contrast to the preference for endo-addition to (167)—(169) by various dienophiles, reaction of l,4-diphenyl-2-benzopyran-3-one (170) leads mainly to the production of exo-adducts. Since 1,3-diphenylinden-2-one also reacted by endo-addition, the exo-selectivity in additions to (170) is explained as resulting from inhibition of attractive endo secondary interactions by non-coplanarity of the phenyl substituents. Related to these results is the finding that isodicyclopentadiene (171) reacts with methyl acrylate under kinetic control to give the syn-adduct (172) a similar result was observed in the addition of methyl... 

The reaction of o-iodophenol, norbornadiene and CO proceeds via alkene and CO insertions to afford the lactone 562, which is converted into coumarin (563) by the retro-Diels-Alder reaction. In this coumarin synthesis, norbona-diene behaves as a masked acetylene[4)3],... 

The cycloaddition between norbornadiene (23 in Scheme 1.12) and maleic anhydride was the first example of a /mmo-Diels-Alder reaction [55]. Other venerable examples are reported in Scheme 1.12 [56]. Under thermal conditions, the reaction is generally poorly diastereoselective and occurs in low yield, and therefore several research groups have studied the utility of transition metal catalysts [57]. Tautens and coworkers [57c] investigated the cycloaddition of norbornadiene and some of its monosubstituted derivatives with electron-deficient dienophiles in the presence of nickel-cyclo-octadiene Ni(COD)2 and PPhs. Some results are illustrated in Tables 1.4 and 1.5. 

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... 

The /lomo-Diels-Alder reaction is a [2 + 2 + 2] cycloaddition of a 1,4-diene with a dienophile which produces two new bonds and a cyclopropane ring. This reaction is an example of a multi-ring-forming reaction that to date has found few applications in synthesis, since the use of 1,4-dienes has been limited mainly to bridged cyclohexa-1,4-dienes and almost exclusively to norbornadiene. Lewis-acid catalysts accelerate /lowo-Diels-Alder reactions and increase the selectivity for the [2 + 2 + 2] vs. [2 + 2] cycloaddition. 

Lewis-acid catalysis is effective in intermolecular as well as intramolecular /zomo-Diels-Alder reactions. Thus, complex polycyclic compounds 93 have been obtained in good yield by the cycloaddition of norbornadiene-derived dienynes 92 by using cobalt catalyst, whereas no reaction occurred under thermal conditions [91] (Scheme 3.18). 

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. 

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