Norbomene, addition

The stereochemistry of the addition of i-PrLi to 7-t-BuO-norbornadiene is exo-cis exo addition also occurred to syn-7-t-BuO-norbomene . Additions of i-PrLi occur to both endo-5-MeO- and endo-5-MeOCH2-bicyclo[2.2.1]hept-2-ene with the i-Pr group occupying an exo position in the product . An alternative reaction occurs with exo-5-MeO-bicyclo[2.2.1]hept-2-ene ° ... 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

The monomer, norbomene (or bicyclo[2.2.l]hept-2-ene), is produced by the Diels-Alder addition of ethylene to cyclopentadiene. The monomer is polymerised by a ring-opening mechanism to give a linear polymer with a repeat unit containing both an in-chain five-membered ring and a double bond. Both cis-and trans- structures are obtainable according to the choice of catalyst used ... 

The stereoselective reactions in Scheme 2.10 include one example that is completely stereoselective (entry 3), one that is highly stereoselective (entry 6), and others in which the stereoselectivity is modest to low (entries 1,2,4, 5, and 7). The addition of formic acid to norbomene (entry 3) produces only the exo ester. Reduction of 4-r-butylcyclohexanone (entry 6) is typical of the reduction of unhindered cyclohexanones in that the major diastereomer produced has an equatorial hydroxyl group. Certain other reducing agents, particularly sterically bulky ones, exhibit the opposite stereoselectivity and favor the formation of the diastereomer having an axial hydroxyl groi. The alkylation of 4-t-butylpiperidine with benzyl chloride (entry 7) provides only a slight excess of one diastereomer over the other. 

The reaction course taken by photoexcited cycloalkenes in hydroxylic solvents depends on ring size. 1-Methylcyclohexene, 1-methylcycloheptene, and 1-methylcyclooc-tene all add methanol, but neither 1-methylcyclopentene nor norbomene does so. The key intermediate in the addition reactions is believed to be the highly reactive -isomer of the cycloalkene. 

Table 2. Products of Addition of Halogen Fluorides to Norbomene...

We will apply these results to data on the addition of m-nitrophenylazide to norbomene in ethyl acetate ... 

A somewhat more complex application of this notion is represented by the CNS stimulant fencamfine (83). Diels-Alder addition of cyclopentadiene and nitrostyrene affords the norbomene derivative, 80. Catalytic hydrogenation reduces both the remaining double bond and the nitro group (81). ° Condensation with acetaldehyde gives the corresponding imine (82) a second reduction step completes the synthesis of fencamfine (83). ... 

By the addition of organotin hydrides to norbomene and norboma-diene, and subsequent reactions of the products, a variety of nor-bomyl-, norbornenyl-, and nortricyclyl-tin compounds has been isolated, and identified (67-69). 

In anti addition to a cyclic substrate, the initial attack by the electrophile is also from the less-hindered face. However, many (though not all) electrophilic additions to norbomene and similar strained bicycloalkenes are syn additions." In these cases attack is always from the exo side, for example," ... 

Addition of RSH to norbomene gave only ejco-norbomyl... 

The endo pyramidization results in the high exo reactivity and, in fact, this pyramidi-zation was confmned by Wipff and Morokuma [37], The orbital distortion also implies large negative electrostatic potential in the exo face. Very recently, Abbasoglu and Yilmaz [38] calculated a derivative of norbomene, i.e., endo tricyclo[3.2.1.0 ] oct-6-ene and confirmed the exo extension of the HOMO accompanied by the endo pyramidization, the large negative electrostatic potential on the exo face, and the preferential exo addition of Br. ... 

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... 

Diels-Alder reaction between isodicyclopentadiene 79 and a variety of dienophiles takes place from the bottom [40], This facial selectivity is contrastive with well known exo (top) facial selectivity in the additions to norbomene 80 [41] (Scheme 32). 

In contrast with exo (top) facial selectivity in the additions to norbomene 80 [41], Diels-Alder reaction between isodicyclopentadiene 79 takes place from the bottom [40] (see Scheme 32). To solve this problem, Honk and Brown calculated the transition state of the parent Diels-Alder reaction of butadiene with ethylene [47], They pointed ont that of particular note for isodicyclopentadiene selectivity issue is the 14.9° out-of-plane bending of the hydrogens at C2 and C3 of butadiene. The bending is derived from Cl and C4 pyramidalization and rotation inwardly to achieve overlap of p-orbitals on these carbons with the ethylene termini. To keep the tr-bonding between C1-C2 and C3-C4, the p-orbitals at C2 and C3 rotate inwardly on the side of the diene nearest to ethylene. This is necessarily accompanied by C2 and C3 hydrogen movanent toward the attacking dienophile. They proposed that when norbomene is fused at C2 and C3, the tendency of endo bending of the norbomene framework will be manifested in the preference for bottom attack in Diels-Alder reactions (Schane 38). 

More success has been had with Ir complexes incorporating permelhylcyclopentadiene and NHC ligands. Complexes 18-20 (Fig. 4.7) were evalnated for norbomene polymerisation following activation with MAO [22]. Complex 19 was the most active, giving a TOF of 12 220 h over 10 min, followed by 18 (TOF = 3 220 h" ), while 20 was inactive, indicating that a hemilabile pendant group seems essential. Analysis (NMR) of the polymers formed with 18 and 19 shows that polymerisation proceeds via an addition (coordination-insertion) mechanism. 

Notably, half of the tertiary product was the telomer 8, which incorporates an additional equivalent of olefin. In contrast, the Pt(0) precatalyst Pt(norbornene)3 (0.2 mol%) gave a 10 1 mixture of tertiary phosphine 9 and telomer 8 over 11 h at 5 5°C in toluene (Scheme 5-10, Eq. 2). The selectivity was higher (>95%) when only the final step [addition of PH(CH2CH2C02Et)2 to ethyl acrylate] was monitored by NMR. In contrast, Pt[P(CH2CH2CF3)3]2(norbomene) did not catalyze addition of PH, to CH2=CHCF3 thus, the olefin must be a Michael acceptor. [11]... 

A recent report by Kropp(85) indicates that whereas 2-norbomene undergoes radical reactions when irradiated in alcohol solution in the presence of a sensitizer, 2-phenyl-2-norbomene and related analogs undergo polar addition of methanol when irradiated directly (photosensitized irradiation led to no products) ... 

Reactions of amines with alkenes have been reviewed298,299. Alkali metal amides are active homogeneous catalysts for the amination of olefins. Thus diethylamine and ethylene yield triethylamine when heated at 70-90 °C at 6-10 atm in the presence of lithium diethylamide and /V./V./V. /V -tetrarncthylcthylcncdiaminc. Solutions of caesium amide promote the addition of ammonia to ethylene at 100 °C and 110 atm to give mixtures of mono-, di- and triethylamines300. The iridium(I)-catalysed addition of aniline to norbomene affords the anilinonorbomane 274301. Treatment of norbomene with aniline... 

It has been reported by R.Scheiner that phenylazide forms triazoline compounds by 1,3-cyclic addition to unsaturated olefines such as n-butylethylene and norbornen(9 ). These triazolines are decomposed photochemically or thermally to give imine compounds and aziridine as is shown in scheme 1. These facts suggest that phenylazide may react with 3-methyl-1-butene to give triazoline in a similar reaction to that with norbomen. 

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