Endo-5-Norbornene

Corey and coworkerssuggested that when the reactant in the Kolb6 reaction is such that the R group will form a relatively stable carbocation, products other than Kolbe dimers (RR) or monomers (RH) may be formed by an additional electrochemical step. To test this idea they oxidized compounds which can generate stable carbocations. For instance, the electrolysis of either exo- or endo-5-norbornene-2-carboxylate (16) in methanol gave 3-methoxynortricyclene (17) in 50 % yield. 

The previous sections surveyed the general electrochemical methods for producing a cyclopropyl ring in a variety of organic systems. In addition to those, more specific methods have appeared occasionally in the literature. Shono and coworkers" studied the anodic oxidation of 2-endo-5-norbornen-2-yl-methanol (29) in three different solvents. Among other products they obtained the tetracyclic system 30 where one of the rings is a cyclopropyl. 

Although carbomagnesiations of disubstituted alkenes proceeds sluggishly, the reaction of endo-5-norbornen-2-ol (5) proceeds in high yield and regioselectivity. However, the reactivity and regioselectivity are decreased in the reaction of the methyl ether of 5. 

Diels-Alder addition of tetrachlorocyclopentadiene dimethylketal to endo-5-norbornene carboxylic acid produces (459). Ketal cleavage (H2SO4), cheletropic loss of CO (reflux in o-dichloro benzene), and aromatization (bromine in hot chlorobenzene) affords the endo-acid (460 X = Cl) which can be dechlorinated by reaction with Ni-Al alloy and alkali to give (460 X = H). The clean retention of stereochemistry in reaction sequence is suggested to be of value in the general synthesis of alicyclic-substituted benzonorbornenes the methyl ester of (460 X = H) can likewise be prepared without epimerization. ... 

Whereas exo-norbornene oxide rearranges to nortricyclanol on treatment with strong base through transannular C-H insertion (Scheme 5.11), endo-norbornene oxide 64 gives norcamphor 65 as the major product (Scheme 5.14) [15, 22]. This product arises from 1,2-hydrogen migration very little transannular rearrangement is observed. These two reaction pathways are often found to be in competition with one another, and subtle differences in substrate structure, and even in the base employed, can have a profound influence on product distribution. 

In the same way, dipyridyl amide-functionalized supports suitable for the SPE of metal ions from aqueous solutions can be prepared. The resins are synthesized via the copolymerization of the functional monomer endo-norbornene-5-yl-N,N-di-2-pyridyl carboxylic amide with a molybdenum-based catalyst (42). Essentially no loss of performance was observed after extensive use over more than twenty cycles. After exposure to air for at least 2 months, a change in color from bright white to yellow was observed. However, this change in color did not influence the characteristic properties of the resins. 

Reaction of exo- or endo-norbornen-2-boronic acid with HgCl2 in aq Mc2CO provides the rearranged 3-chloromerciuritricyclo[2.2.1.0 ]heptane ... 

Fig. 9.4 ORTEP representation of cis-Pt( /2-C,O-(endo,endo)-norbornene-COOCH2CH3)(P(CH2CH3)3). ...

Nortricyclyl and Quadricyclyl Systems.—The studies of the kinetics of acid-catalysed hydration of exo- and endo-norbornen-2-ols, referred to above, have been extended to include 3-nortricyclanol, 1-methyl-cis- and -rra s-3-nortricyclanols, and 3-methyl-3-nortricyclanol. Solvent deuterium-isotope effects are interpreted in favour of an A-S 2 hydration of the three-membered carbon ring of the secondary alcohols, or an A-1 mechanism for the tertiary alcohol in which case the rate-determining step is the formation of a carbocation (probably the 3-methyl-3-nortricyclyl cation) by elimination of water. 

An example of the use of NMR spectroscopy to ascertain with reasonable certainty the stereochemistry of a series of enamines has been provided by Paquette (25). Based on a study of the NMR spectra of the endo- and exo-5-norbornene-2-carboxaldehydes (168), the enamine mixtures were estimated to contain 80 to 90 % of the transoid form (170). 

The stereoselectivity of epoxidation with peroxycarboxylic acids has been well studied. Addition of oxygen occurs preferentially from the less hindered side of the molecule. Norbornene, for example, gives a 96 4 exo endo ratio.76 In molecules where two potential modes of approach are not very different, a mixture of products is formed. 

The reactions with quadricyclane, shown in Eq. (31), gave products identical to those formed by the same silene reacting in a [2 + 2] manner with norbornene. Mixtures of exo endo isomers were frequently observed. Again, only silenes of the Auner type have been studied with this reagent,51-53,185,188 so it is not known whether the Wiberg- or Brook-type silenes will undergo this mode of cycloaddition. 

The polymerization of several different protected monomers was executed with the molybdenum initiator. Two types of norbornene templates were generated as mixtures of diastereomers one class possessed a single saccharide substituent attached through either an endo or exo ester group, and the other was equipped with two carbohydrate residues appended to the bicyclic scaffold... 

The greater rate of dehydration of 2-exo- over 2-endo-norbornanol can be interpreted by an anchimeric assistance which involves the delocalization of C(l)-C(6) bonding electron pair this helps in the removal of a hydroxyl ion and facilitates dehydration. This delocalization is probably responsible for the formation of norbornene as one of the primary products of dehydration. 

N-BND A-benzyloxycarbonyloxy-5-norbornene-endo-2,3-dicarboximide N-IBND A-butoxycarbonyloxy-5-norbornene-endo-2,3-dicarboximide... 

Scheme 61) [2b, 150], but can give rise to a variety of products. With unsym-metrically substituted alkenes of type 266, two regioisomeric products were obtained, but the isomer 268 bearing the ester group near the spiro atom was the minor component in all cases. Norbornadiene and norbornene react with 1 by the same mode to give formal [3 -F 2] cycloadducts 269 and 270, respectively, the latter as a 9 1 mixture of exo- and endo-isomers. 

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. 

The photocycloaddition reaction is subject to the usual directive forces caused by steric interaction during the approach of most reagents. For example, the photocycloaddition of benzophenone to norbornene gives primarily the exo oxetane 47 with little or none of the endo isomer... 

The predominance of exo product is expected since the exo position of norbornene is more easily approached than the endo. 

The Diels-Alder reaction is stereo specific. The stereochemistry of the dienophile is retained in the product i.e., cis and trans dienophiles produce different diastereoisomers in the product. For example, freshly distilled cyclopentadiene, having s-cis configuration, reacts with maleic anhydride to give c/ -norbornene-Sjh-endo-dicarboxylic anhydride. 

Although it is generally accepted that the exo approach to norbornene is favored over the endo, the magnitude of the AAE is rarely measurable experimentally unless some fraction of the endo product can be detected. The exo approach to norbornene is favored over the endo orientation by nearly 3 kcal mol "1 for both PFA and DMDO, while the exo TS for benzonorbomadiene is favored by nearly 5 kcal mol-1 (Figure 27). The preferred exo approach does not appear to result from steric interactions. It is of particular interest that the A for norbornene is only 0.9 kcal mol-1 greater than that for cyclohexene despite the SE = 19.2 kcal mol 1 for the strained bicyclic alkene. Thus, in the absence of twist-strain we observe little rate enhancement due to strain energy. 

The course of the reaction of furan and DMAD is temperature dependent (73CJC4125). The initially formed monoadduct (118) acts as a dienophile and further addition of furan can occur at the di- or tetra-substituted double bonds. In such additions to norbornene-type dienophiles the diene is subject to steric approach control and approach to the exo face is preferred. At 25 °C the tetrasubstituted double bond acts as a dienophile and the endo,exo... 

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