Nortricyclenes

The above assumes that C protonation is not excluded for steric reasons. Thus N protonation takes place with derivatives of dehydroquinuclidine and the alkaloids neostrychnine and trimethylconkurchine (( ). N protonation was also believed to occur in the case of 2-N-hexamethyleneimino-bicyclo[l,2,2]-2-heptene, which was believed to give the nortricyclene derivative (6) on protonation with perchloric acid. Later work, however, showed the salt to be the results of C protonation (15) and to have structure 7. 

The stable 2-norbornyl cation has recently been shown to be a non-classical, unusually stabilized species. Olah et al. (1970) proved spectroscopically that this ion is a comer-protonated nortricyclene with a pentavalent carbon atom. The value for the carbonylation-decarbonyla-tion equilibrium constant K (= of the 2-norbomyl ion illustrates... 

The peroxide-catalysed addition of dimethyl phosphonate to norborna-diene gives nortricyclenes as well as norbornenes. Usually, radicals react with this diene to give only nortricyclene derivatives. The ease of hydrogen abstraction from the parent phosphonate undoubtedly favours trapping of radical (8). 

In a series of experiments using various pressures of CO and H 0, with norbornadiene as the diene /44, 45/, we were able to verify an earlier suggestion /43/ that the 1,2 addition product norbornene is formed through a diene dissociation (Equation 43) and the 1,5 addition product nortricyclene through a CO dissociation (Equation 42). 

At high hydrogen pressures, norbornane is formed by hydrogenation of a nortricyclene precursor /45/. 

Carbene 103 undergoes 1,3-CH insertion to nortricyclene (105), but this reaction is either too rapid for LFP measurement by the pyridine ylide method (r <0.1 ns), or the insertion occurs by RIES of the precursor 2-norbomyldiazirine. Theoretically, a short lifetime is expected for 103 AG for the carbene insertion into the 6-endo-CU bond (103 — 105) is computed at 5.2 kcal/mol, about 6.7 kcal/mol less than the (unobserved) exo- 1,2-H shift to norbomene.16... 

Similar low activities were found in the hydrogenation of 1-octene [47]. The use of [Ni(PPh3)2I2] in the hydrogenation of norbomadiene resulted in considerable amounts of nortricyclene, via transannular ring closure, whereas 1,5-cyclo-octadiene yielded bis-cyclo-[3.3.0]oct-2-ene. According to these authors, the re-... 

The unusually pronounced shielding effect on the C(7) methylene group of an annelated three-membered ring, as in 85 (202,203), 86 (371), and 250 (372), has already been mentioned (cf. Section III-C) and exists also, although to a somewhat lesser extent, in nortricyclene (251) (373). 

Dehydronorbomylverbindungen gehen bei manchen chemischen Um-setzungen ungewohnlich leicht in Derivate des einen Cyclopropanring enthaltenden Nortricyclens (I) fiber. 

Alder, K., u. F. Brochhagen Synthese von Nortricyclen-Derivaten. Chem. 

Lippincott, E. R. The Raman Spectra of Nortricyclene. J. Amer. chem. 

Electrochemical reduction of 2,2-dichloronorbomane, 2-exo-bromo-2-endo-chloronorbomane, and 2-endo-bromo-2-e%o-chloronorbornane gives mixtures of nortricyclene and endo-2-chloronorbor-nane [48]. Electrolysis of 1-bromo-... 

Nortricyclene is the only product of dehydration of 2-ewdo-norbornanol in the presence of the modified alumina. With longer contact time especially at higher temperature, the nortricyclene isomerizes to norbornene. 2-ea o-Norbornanol forms 70% nortricyclene and 30% norbornene. 

In order to explain the formation of nortricyclene from 2-ea o-norbornanol, it is necessary to assume a back side attack at the hydrogen attached to carbon 6. The general mechanism here is similar to the trans elimination reaction as discussed under menthol, 1,4-cyclohexanediol, and bornanols. 

The non-classical ion may exist as edge or face protonated nortricyclene, represented by stmcture [9], as an alternative. This species is not a resonance stmcture of [7] or [8]. If it is a discrete intermediate, one might expect to be able to detect the displaced proton via a suitably designed exchange experiment. 

C and H Nuclear Magnetic Resonance Chemical Shifts and Coupling Constants in the Norbomyl Cation, Cyclopentyl Cation, Nortricyclene, and... 

These spectral changes are consistent with either (a) freezing out a stable non-classical ion, or (b) the presence of the classical ion in which the 6,2-hydride shift has been slowed down, but the Wagner-Meerwein rearrangement is still exceedingly rapid. If the ion is non-classical, the spectrum indicates that it must be a comer-protonated nortricyclene rather than the edge-protonated ion because the latter would have split into a 1 2 1 pattern. 

The norbomyl cation and substituted nortricyclenes were shown to have five relatively weak bands in the C—H stretching region ( 3000 cm ). Only three were present in norbomane and its derivatives, and these were generally at lower frequency than those in the ion. 

In the C—C stretching region, the norbomyl ion and nortricyclene exhibit very strong peaks at 952 and 951 cm and similar spectra between 700 and 1000 cm . The alkylnorbomyl cations, 2-methyl and 2-ethyl, on the other hand, show substantial similarities to norbomane in this region. 

SbFs-FSOaH-SOj e o-2-Chloro- norbomane Low Pyridine Nortricyclene... 

SbFj-FSOaH-SOj exo-2-Chloro- norbomane Low (MeO") MeOH 1 Nortricyclene and exo-2-norbomyl methyl ether... 

Also inconclusive are the results of the quenching experiments shown in Table 12. Thus, reaction of the ion with pyridine has been reported to yield nortricyclene, while water and methanol yield mainly 2-exo-norbomyl derivatives. If the ion is classical, the production of alcohols and methyl ethers is regarded as due to condensation of it and water, methanol, or methoxide. The production of nortricyclene would then be regarded as due to a deep seated reaction of pyridine with ion [2] leading to a transition state resembling pyridine, a proton and nortricyclene. 

If the ion is non-classical, nortricyclene may be viewed as the expected deprotonation product, while the hydrolysis products arise from a deep seated rearrangement to a transition state resembling the classical ion and the nucleophile. 

Norbornadiene is also known to add electrophilic or free-radical reagents across the 2- and 6-positions with formation of nortricyclene derivatives (85). Neither type of adduct, 84 nor 85, has yet been obtained from 7-azabicyclo[2.2.1]heptadiene derivatives, but aromatiza-tion of the latter is induced by some electrophilic reagents (see Section II,E). 

Also, in the halogenation of XXb with cyanogen bromide the predominate product was the nortricyclenic bromide (XXIIIa and b, X = Br) the treatment of XXIa with iodine monochloride yields the endo-nortricyclenic iodide (XXIIIa, X = I). Thus the mechanism appears to involve attack of a positive halogen with predominate retention of configuration at carbon. 

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