Norbornene adduct

DFT and ab initio studies of the cycloaddition reaction between methyleneketene and cyclopentadiene indicated that the norbornene adduct is the primary reaction product from a 1,2-addition.131 The thermal 4 + 2-cycloaddition of o-xylylenes (104) with /3-nitro-me.S 0-tetraphenylporphyrin (103) produced a high yield of the chlorin (105) together with low yields of the naphthoporphyrin (106) and the bis-naphthoporphyrin... 

The tungsten(II) carbonyl complex (CO)4W(/u.-Cl)3W(SnCl3)(CO)3 has been identified as a very effective catalyst for the hydroarylation of norbornene conducted in arene solution at room temperature. Norbornene adducts with benzene, toluene, p-xylene, and mesitylene have been isolated. On the basis of XH NMR monitoring of several catalytic reactions, a possible mechanism, involving coordination of norbornene to the W(II) atom and its activation, has been proposed.123... 

The S3N3+ cation is an interesting example of an antiaromatic Sjr-electron system. Ab initio Cl 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 norbornene adduct, but salts of the free cation have not been isolated. 

Direct Wittig reaction of Ph PCHCOn,Me with the four unsubstituted D-aldopentoses followed by acetylation provides convenient preparative access to acyclic seven-carbon trans-2.3-unsaturated sugar derivatives. These products served as dienophiles for a detailed comparative study in Diels—Alder cycloaddition with cyclopentadiene. Related syntheses afforded analogous cis-dienophiles. Cycloaddition under uncatalyzed thermal conditions gave mixtures of the four possible stereoisomeric norbornene adducts. The endo, exo ratios, and diastereofacial selectivities of the adducts were determined by NMR spectroscopy and by chemical transformations, supplemented by selected X-ray crystallographic analyses. Different distributions of isomers were encountered when a Lewis acid was used to catalyze the cycloaddition. The reaction can be controlled to provide preparative access to selected isomers and thus constitutes a versatile method for chirality transfer from the precursor sugar to four new asymmetric centers in a carbocyclic framework. 

The cyclohexadiene derivative 130 was obtained by the co-cyclization of DMAD with strained alkenes such as norbornene catalyzed by 75[63], However, the linear 2 1 adduct 131 of an alkene and DMAD was obtained selectively using bis(maleic anhydride)(norbornene)palladium (124)[64] as a cat-alyst[65], A similar reaction of allyl alcohol with DMAD is catalyzed by the catalyst 123 to give the linear adducts 132 and 133[66], Reaction of a vinyl ether with DMAD gives the cyclopentene derivatives 134 and 135 as 2 I adducts, and a cyclooctadiene derivative, although the selectivity is not high[67]. 

Early work established that S4N4 forms di-adducts with alkenes such as norbornene or norbomadiene. Subsequently, structural and spectroscopic studies established that cycloaddition occurs in a 1,3-S,S"-fashion. The regiochemistry of addition can be rationalized in frontier orbital terms the interaction of the alkene HOMO with the low-lying LUMO of S4N4 exerts kinetic control. Consistently, only electron-rich alkenes add to S4N4. 

Formation of mixtures of products in these reactions can be attributed largely to the properties of the acetate group. The reactions of a number of cycloalkenes with thallium(III) salts have been investigated in some detail and the results obtained have served both to elucidate the stereochemistry of oxythallation and to underline the important role assumed by the anion of the metal salt in these oxidations. The most unambiguous evidence as to the stereochemistry of oxythallation comes from studies by Winstein on the oxythallation of norbornene (VII) and norbornadiene (VIII) with thal-lium(III) acetate in chloroform, in which the adducts (IX) and (X) could be precipitated from the reaction mixture by addition of pentane 128) (Scheme 11). Both by chemical means and by analogy with the oxymercuration... 

Intermolecular bis-silylation of unactivated alkenes has been achieved initially with a zerovalent platinum catalyst such as Pt(PPh3)4 (Equations (30) and (31)).101 1,2-Difluorotetramethyldisilane undergoes addition to ethylene and norbornene in the presence of Pt(PPh3)4 catalyst at 150 °G to give the corresponding adducts in 95% and 26% yields, respectively. For the addition of 1,2-diphenyltetramethyldisilane to ethylene, Pt(PMe3)4 (33% yield) was found to be more active than Pt(PPh3)4 (4% yield). 

The DMS method has not been employed yet for the generation of 117 and 123, since the dibromocarbene adducts of norbomadiene and norbornene rearrange under the usual conditions for the preparation [89]. However, they could be synthesized at -60 °C by taking advantage of tetrabromomethane and methyllithium as a source of the carbene [90] and could prove stable enough to serve as precursors of 117 and 123. On the other hand, the adducts of bromofluorocarbene to norborna-diene and norbornene having the fluorine atom in a cis-orientation should be isol-able at room temperature and hence be usable as stable precursors of 117 and 123. These variations ofthe DMS method were published on the occasion ofthe preparation of cycloadducts of l-oxa-2,3-cyclohexadiene (351) (Section 6.3.6) [35, 91], 1,2,4-cyclohexatriene (162) and 3d2-lJ-f-naphthalene (221) (Section 6.3.4) [35, 92],... 

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. 

The initial step of the cycle forming 23 was supported by separate stoichiometric reachons involving similar Ir(I) complexes that oxidatively added the N—H bond of aniline (see Section 6.5.2). It should be noted that norbornene does not form stable adducts with electron-rich Ir(I) complexes such as those used in this catalysis (R. Dorta and A. Togni, unpublished results). 

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... 

The 1,4-cycloadditions gave the diexo adducts stereoselectively from norbornene, and cis adducts in the cycloalkene series. 

Studies by the submitters have indicated that the procedure reported here is the preferred method for the preparation of bicyclo[3.2.1]octan-3-one. It employs readily available, inexpensive reagents, and the overall yield is good. In addition, the method can be used for the synthesis of the difficultly accessible next higher homologues of bicyclo[2.2.2]oct-2-ene as well as for derivatives of norbornene. Bicyclo[3.2.2]nonan-3-one and l-methylbicyclo[3.2.1]octan-3-one have been prepared by a similar route6 in 60% and 47% yields, respectively (based on adduct). However, the preferred procedure for the formation of the dichlorocarbene adduct of bicyclo[2.2.2]oct-2-ene is that of Seyferth using phenyltrichloromethylmercury. Even in this case the overall yield is moderate (37%). 

Irradiation of the epoxy dinitrile 90 in a solution of acetonitrile formed the stabilized ylide 91 that was trapped with ethyl vinyl ether, producing both exo and endo adducts 92 and 93 in 25 and 8% yields. Studies with other dipolarophiles (27) such as norbornene and methyloxazoline generated cycloadducts 94 and 95, respectively, in low overall yield. 

By treating norbornene with benzenesulfonyl azide in benzene at room temperature, a crystalline product is obtained in quantitative yield.264-265 On the basis of chemical and nmr evidence, an aziridine structure (85) similar to exo-2,3-epoxy-norbornene (86) is attributed to the adduct. The addition thus occurs at the least hindered exo side of the bicyclic nucleus. 

Diels-Alder additions provide one of the more extensively studied reactions of these heteroles, and many examples are listed in the reviews given at the beginning of this section. Typical additions often require heating, giving the 7-hetero-norbornenes and -norbor-nadienes as products of reaction with alkenes and alkynes (Scheme 209). The report that (131) resulted at room temperature from tolane and (120) was therefore surprising. Subsequent investigation showed it to be a 1 1 crystalline adduct from which tolane could be sublimed (Scheme 210) (72CC690). 

When acrylonitrile or ethyl acrylate was used as the dipolarophile, the azomethine adducts (134) and (135) were formed no thiocarbonyl ylide addition products were isolable in refluxing toluene or xylene, although the isoindoles (136a) and (136b) derived from them were isolated. In contrast to the reactions with fumaronitrile or AT-phenylmaleimide, the azomethine adducts (134) and (135) were still present at higher reaction temperatures — almost 50% in toluene and 4-5% in xylene. Under the same reaction conditions other electron-deficient dipolarophiles like dimethyl fumarate, norbornene, dimethyl maleate, phenyl isocyanate, phenyl isothiocyanate, benzoyl isothiocyanate, p-tosyl isocyanate and diphenylcyclopropenone failed to undergo cycloaddition to thienopyrrole (13), presumably due to steric interactions (77HC(30)317). 

Condensed pyridines were obtained when 1,2,4-triazines reacted with cyclic alkenes. Trichloro-l,2,4-triazine (73) afforded the condensed pyridines (370a, b) in high yield with cyclopentene and (Z)-cyclooctene, respectively. In the reaction with cyclopentene the bis adduct (371) was isolated in small amount but the bis adduct (372a) is the sole reaction product when (73) is treated with norbornene. The more reactive trifluoro-1,2,4-triazine (325) affords bis adducts (371b, c 372b) with cyclopentene and (Z)-cyclooctene as well as with norbornene (79CC658). 

Other 1,2,4-triazines react with norbornene to give either the condensed pyridines (375) and/or the bis adducts (372). The ratio of the two products depends on the reaction conditions and the relative proportions of reactants (69TL5171). 

The addition of aliphatic aldehydes and ketones to alkenes is less successful as a preparative procedure for oxetanes. An essential requirement for addition is that the triplet energy of the alkene must be considerably greater than that of the carbonyl. If this condition is not fulfilled, energy transfer to the alkene can occur,279 sensitizing, for example, dimerization of the alkene. This is clearly illustrated 280, 281 for norbornene (264) which on irradiation in the presence of benzophenone (ET 68.5 kcal/mole) forms the adduct 265 photolysis in acetone (ET 75 kcal/mole) affords only norbornene dimers (266 and 267), whereas acetophenone, which has intermediate triplet energy (Et 73.6 kcal/mole) forms both oxetanes and norbornene dimers. 

The meso-ionic l,3-dithiol-4-ones (134) participate464-77 91-93,94 in 1,3-dipolar cycloaddition reactions giving adducts of the general type 136. They show a remarkable degree of reactivity toward simple alkenes94 including tetramethylethylene, cydopentene, norbornene, and norbor-nadiene as well as toward the more reactive 1,3-dipolarophilic olefins dimethyl maleate, dimethyl fumarate, methyl cinnamate, diben-zoylethylene, JV-phenylmaleimide, and acenaphthylene. Alkynes91-93 such as dimethyl acetylenedicarboxylate also add to meso-ionic 1,3-dithiol-4-ones (134), but the intermediate cycloadducts are not isolable they eliminate carbonyl sulfide and yield thiophenes (137) directly.91-93... 

The reaction of aryl azides with a number of 7-substituted norbornenes and norbornadienes has been investigated (Scheme 14).128 Although bulky substituents in the 7-position slow down addition,43-45 good yields of adducts have been obtained in most cases by carrying out the reaction for several days. NMR analysis indicates exclusive exo stereochemistry for the products, and when the 7-hydroxyl is in the anti position, the direction of azide addition is reversed (Scheme 14)."... 

A second example is the formation of an endo-triazoline from a chloronor-bornyltriazene compound, apparently by an intramolecular nucleophilic displacement reaction (Scheme 106).373 Direct azide addition to norbornene is known to lead exclusively to the exo adducts (Section II,A,1). 

Exo-endo additions of organic azides to the norbornene skeleton and other bridged bicyclic systems can be easily differentiated from the NMR spectra of the adducts. The endo protons (exo adducts) of the norbornane do not couple with the bridgehead hydrogens.386 The endo protons in position 3a and 7a of adduct 65 exhibit an AB spectrum. The lack of coupling with the bridgehead protons is a result of a dihedral angle of 82°.25,96 Based on this, the exo form of cycloadduct 66 exhibits symmetrical doublets centered at 8 4.60 and... 

In some thermolysis reactions, amines (90 and 91) have been characterized.108,111,112,457 When R1 = CH2OH and R2 = H in Scheme 164, the aziridine undergoes spontaneous rearrangement (Scheme 166).125 An endo-triazoline adduct from norbornene yields a polymer as the principal... 

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