Norbomenes, addition reactions

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. 

The course of addition reactions of ROH-XeF2 to alkenes has been elucidated using norbomene, 2-methylpent-2-ene and hex-l-ene as model substrates. It turned out that the alkoxyxenon fluoride intermediates (ROXeF) can react either as oxygen electrophiles (initially adding alkoxy substituent) or as apparent fluorine electrophiles (initially adding fluorine), depending on the reaction conditions. Simple addition of poorly nucleophilic alcohols to norbomene was also observed in certain instances. Selectivity between the various reaction pathways (simple fluorination, alkoxyfluorina-tion, or alcohol addition) proved to be sensitive to various reactions conditions, especially solvent, temperature, and catalyst.27... 

Acyl isocyanates are more reactive than alkyl or aryl isocyanates. However, the presence of an additional rr-bond conjugated to the C>i-N bond of the isocyanate opens the possibility for [4 + 2] cycloadditions to compete with normal [2 + 2] additions. Reactions with alkyl and aryl substituted alkenes are rather slow. Propene, tranj-2-butene, styrene and conjugated dienes give only 3-lactams, albeit in moderate yields (Scheme 25). The strained double bond of norbomene, a reactive dienophile, adds across the conjugated 4iT-system of trichloroacetyl isocyanate (equation 51). 

Figure 12 shows the behavior of different terpolymers as a function of the unsaturation and the peroxide content in the formulation. The unusual trend of (V)-EPTM can be explained by the existence of another cross-linking mechanian (self-vulcanization) besides the radical one (see the next Section), while the high yield of cross-links displayed by 5-methylene-2-norbomene-EPDM is due to the high reactivity of the radical originating from the methylene double bond which undergoes, preferentially, addition reactions instead of coupling processes ... 

Complex 6 reacted with cyclopentadiene at ambient temperature ( ) in toluene in a J4+2]-cyclo-addition reaction to give phospha-norbomene complex 11 ( P NMR -69.1 ppm, 7(P,W) = 204.5 Hz), which reacted during the column chromatography to fiimish the / -H-substituted phospha-norbomene complex 12. Although complex 12 was fully characterized by NMR and MS spectroscopy, the confirmation was only tentatively assigned (Scheme S). 

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 ° ... 

As trialkyl(aryl)stannanes have never been reported to undergo oxidative addition with a palladium(O) or nickel(O) complex, the corresponding arylstannylation is not known. As shown in Scheme 5.7.24, Kosugi and coworkers found that the use of aryl(trichloro)stannanes instead of the trialkyl derivatives enables the palladium-catalyzed arylstannylation of norbomene. The reaction using other unsaturated hydrocarbons including ordinary alkenes has not been reported, but the observation that aryl-tin bonds can be activated by palladium(O) complexes has certain significance, and will lead to future development of other arylstannylations. 

Under the reaction conditions, phenylacetylene was found to be a much more reactive coupling partner than arylboronic acids in the analogous Suzuki-Miyaura coupling, as in addition to the desired product (38), alkynylation and further addition reactions occurred with a variety of transient palladium(II) species (Scheme 27). Despite these undesired side reactions, Catellani was able to fine-tune the reaction conditions to form predominantly product 38 or 39. The formation of the desired product 38 (and suppression of product 39) is promoted by acceleration of norbomene carbopalladation by KOAc [47] and by using an excess of alkyl halide affording several structurally similar unsymmetrical alkyne products in good yields (Scheme 28). 

Esterification. Add-catalyzed esterification of carboxylic acid with alcohol produces water as a coproduct. However, a greener method of esterification of carboxylic acid is via the addition of olefin, which does not produce any co-products and therefore, displays 100% atom efficiency. Proton-exchanged montmorillonite (H+-mont) can be used as a catalyst for addition reactions of carboxylic acids to alkenes (Fig. 7) (38)a). For example, the reaction of benzoic acid with norbomene in the presence of the H+-mont catalyst gave 2-benzoyloxynorbomane. Even with less-reactive simple alkenes, such as cyclopentene and cyclohexene, the corresponding esters were obtained in excellent yields. 

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 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. 

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). 

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). 

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. 

The study of alkene insertions in complexes containing diphosphine ligands turned out to be more complicated than the study of the CO insertion reactions [13], When one attempts to carry out insertion reactions on acetylpalladium complexes decarbonylation takes place. When the reaction is carried out under a pressure of CO the observed rate of alkene insertion depends on the CO pressure due to the competition between CO and ethene coordination. Also, after insertion of the alkene into the acetyl species (3-elimination occurs, except for norbomene or norbomadiene as the alkene. In this instance, as was already reported by Sen [8,27] a syn addition takes place and in this strained skeleton no (3-elimination can take place. Therefore most studies on the alkene insertion and isolation of the intermediates concern the insertion of norbomenes [21,32], The main product observed for norbomene insertion into an acetyl palladium bond is the exo species (see Figure 12.8). 

In addition to the role of substituents in determining regioselectivity, several other structural features affect the reactivity of dipolarophiles. Strain increases reactivity. Norbomene, for example, is consistently more reactive than cyclohexene in 1,3-dipolar cycloadditions. Conjugated functional groups also usually increase reactivity. This increased reactivity has most often been demonstrated with electron-attracting substituents, but for some 1,3-dipoles, enamines, enol ethers, and other alkenes with donor substituents are also quite reactive. Some reactivity data for a series of alkenes with a few 1,3-dipoles are given in Table 6.3. Scheme 6.5 gives some examples of 1,3-dipolar cycloaddition reactions. 

The reaction proceeds smoothly and gives 326 in 43% yield. The stereochemistry of the addition is exo with respect to the norbomene moiety and in line with the usual cycloaddition behavior of quadricyclane [358]. The norbomene double bond in 326 is easily accessible by electrophiles, and, for example, the anti-addition of benzenesulfenyl chloride proceeds quantitatively at room temperature (Scheme 4.66). 

---