2-Norbornyl alcohol

Norbornadiene, 58, 73 2-Norbornyl alcohol, 58, 78 2-Norbornyl fluoride, 58, 78 NUCLEOPHILIC a sec-AMINOALKYLATION, 58,113... 

Geurink and Klumpp measured the protodelithiation enthalpies of 3-lithiopropyl methyl ether, 3-lithiobutyl methyl ether, 5-lithiopentyl methyl ether and 7-5yn-methoxy-2-exo-lithionorbornane in the same study that was discussed in an earlier section for the non-oxygenated compounds n-propyl lithium, n-butyl lithium, 5ec-butyl lithium and 2-norbornyl lithium. The reaction enthalpies for the oxygen-containing lithium species with 5ec-butyl alcohol in benzene were —190 2, —199 4, —190 3 and —199 2 kJmoU, respectively, where all of the lithiated ethers purportedly exist as tetrameric species. 

If the classical structure were correct, the 2-norbornyl cation would be a usual secondary carbocation with no additional stabilization provided by c-delocalization (such as the cyclopentyl cation). The facts, however, seem to be to the contrary. Direct experimental evidence for the unusual stability of the secondary 2-norbomyl cation comes from the low-temperature solution calorimetric studies of Arnett and Petro.75 In a series of investigations, Arnett and Hofelich76 determined the heats of ionization (AHi) of secondary and tertiary chlorides in SbF5-SC>2ClF [Eq. (3.131)] and subsequently alcohols in HS03F-SbF5-SC>2ClF solutions [Eq. (3.132)]. 

Very similar product mixtures are obtained from electrochemical decarboxylations or deoxidations 201 and deaminations 202 of the corresponding alcohols or amines. Anodic oxidation of cyclobutanecarboxylic acid affords in 30% yield a mixture of cyclopropylcarbinol, cyclobutanol and allylcarbinol identical in composition with that obtained from deamination of cyclobutylamine 203 Electrolysis of exo- or encfo-norbornane-2-carboxylic acid gave exo-norbornyl-2-... 

Enholm [13] has also described the synthesis of soluble designer supports by the ring-opening metathesis polymerization (ROMP) of norbornyl derivatives. Reduction of norbornene-l-carboxaldehyde 88 to the corresponding alcohol 89, followed by treatment with either 2-bromopropionic acid or 2-bromo-2-phenylacetic acid in the presence of DCC, provided the esters 90 or 91 respectively (Scheme 19). Polymerization of 90 and 91 was carried out with Grubbs catalyst and halted after 25 s by capping with excess ethyl vinyl ether to give polymers 92 and 93 respectively. 

Coates and Fretz have investigated some substituent effects on their 9-penta-cyclononyl system and found results which support a trishomocyclopropenium ion intermediate. Solvolysis of either the tertiary or secondary methyl-substituted p-nitrobenzoates 115 or 116 in 65 % acetone at 100 °C furnished the same 80 20 mixture of tertiary and secondary alcohols. Similarly, both phenyl-substituted p-nitrobenzoates gave a 94 6 mixture of tertiary to secondary alcohols. Also, the methyl and phenyl substituent effects on 115 are very much lower than those observed for the corresponding 7-norbornyl system (10 and 10, respectively) indicating a stabilized, delocalized intermediate for the reaction of 115. 

As could be predicted from the surface nature of the reaction, when exo-2-norbornyl bromide 144 was exposed to Rieke magnesium at — 70"C in the presence of f-butyl alcohol-OD, the resulting product was exclusively exo-norbornane-2-D, 142. On the other hand, when endo-2-norborny bromide was reacted under the same conditions a 50 50 mixture of endo- and e.xo-norbornane-2-D, 143 and 142, was formed (Scheme 44a). 

Preparation of the norbornyl cation by protonating nortricyclane, or from reaction of norbornyl fluoride or alcohol with SbF5, precludes equilibration involving dinorbomylhalonium ions, but that complication can occur under certain conditions between norbornyl chloride or bromide and the norbornyl cation. We have studied equilibration of the norbornyl cation with excess norbornyl halides through the dinorbomylhalonium ions, and described its characteristics. 

With the norbornyl-2 radical, the high stereoselectivity in favor of the exo alcohol [19] is well explained by the free-radical structure. This one, clearly pyramidal [37-38], with the expansion of the orbital towards the exo direction (Scheme 12). 

In the elimination of HOTs from exo-2-norbornyl tosylate using the sodium salt of 2-cyclohexylcyclohexanol in triglyme at 80 °C, syn-exo elimination is at least 100 times faster than anti elimination. If 18-crown-6 is added, the rate ratio falls to ca. 15 1, indicating that the presence of the sodium cation is important in the complex transition state of the syn process. Pyrolysis of urethanes of borneol and isoborneol has been re-examined and found to give mixtures including a-pinene, tricyclene, camphene, and alcohols. Pyrolysis of nitrobenzoates gives no alcohols but camph-ene, tricyclene, and bornene. ... 

Menthyl alcohol reacts with dichlorocarbene under phase transfer conditions to yield predominantly /-menthyl chloride, a fact which suggests that an SNi pathway is important although not unique. A significant amount of leakage into the sequential or carbonium ion pathway probably accounts for the production of almost equal amounts of exo and e small amounts of formate esters are isolated in these reactions, suggesting that hydrolysis of II occurs but is not a major process. Several examples are recorded in Table 3.2. 

The initial studies centered on the 1-norbomyl halides 8. On irradiation in CH3OH, they afford a mixture of the reduction product norbornane (9) and the ether 10, with the former predominating from bromide 8b and the latter from iodide 8a. The reduction product 9 arises via abstraction of a hydrogen atom by 1-norbornyl radical from the medium and ether 10 via nucleophilic trapping of the 1 -norbornyl cation. Irradiation of either hahde in CH3OD afforded ether 10 with no detectable incorporation of deuterium, indicating that it does not arise via acid-catalyzed addition of the alcohol to an initially formed unsaturated intermediate such as the bridgehead alkene 12 or the propeUane 13. 

Since they are difficult to form, bridgehead cations are highly reactive. Irradiation of hahdes 8 in a variety of media provided a convenient means of exploring the remarkable reactivity of the 1-norbornyl cation (18). It was efficiently trapped by diethyl ether and THE to afford the ethers 19 and 20. Even in aqueous THE, a substantial portion of the butenyl ether 20 was obtained. Trapping by t-butyl alcohol afforded some of the ditertiary ether 21 but was accompanied by formation of 1-norbornanol (22) and 2-methylpropene. Cation 18 was trapped by CHjClj to afford chloride 23, and in aqueous CH3CN the Ritter product 24 was formed. It should be noted that radical abstraction from CH2CI2 occurs at H and ionic abstraction at CL... 

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