2-Norbornyl acetate

For example, acetolysis of exo-2-norbornyl brosylate 254 produces exclusively exo-2-norbornyl acetate 255. The exo-brosylate 254 is more reactive than the endo-brosylate 256 by a factor of 350 and the acetolysis of optically active exo-brosyl ate gave completely racemic exo-acetate 255. Thus, the carbonium ion produced from exo-254 is more rapidly (thus more easily) formed than that from endo-256. These results were originally rationalized in term of a bridged (nonclassical) cation 257 (Winstein approach) (97) or as the rapidly equilibrating classical carbonium ions 258 and 259 (Brown approach (98, 99)). 

Norbornyl acetate, 202 2-Norbornyl brosylate, 202 D-Normorphinan, 356 Nucleophilic additions, 209-242 Nucleophilic 1,4-additions, 221-242... 

It is well known that acetolysis of both exo-2-norbornyl brosylate (2.17) and endo-2-norbornyl brosylate (2.18) produces exclusively exo-2-norbornyl acetate (2.19). However, 2.17 is 350 times more reactive than 2.18 (Scheme 2.13). Further, optically active 2.17 gives... 

Fig. 13. Apparent activation energies (Eg) for acid-catalyzed reactions of exo- and cndo-2-norbornyl acetate and AH for equilibration. (Reproduced from Goering, H. L., Schewene, C. B. J. Am. Chem. Soc. 87. 3516 (1965).]...

Table 1. Calculated and Experimental Isotopic Distribution for the 2-Norbornyl Acetate Formed on Acetolysis of 2-exo-Norbomyl [2,3- C]brosylate ...

The acetolyses of both exo-2-norbornyl brosylate and cndo-2-norbornyl brosylate produce exclusively eaco-2-norbornyl acetate. The exo-brosylate is more reactive than the endo-brosylate by a factor of 350, as measured by their first-order rate constants. Furthermore, acetolysis of optically active exo-brosylate gave completely racemic exo-acetate, and endo-brosylate gave exo-acetate that was at least 93% racemic. 

FIGURE 21.48 Both endo- and exo-2-norbornyl tosylate react in acetic acid to give ca o-2-norbornyl acetate. The reaction of the exo isomer is faster. 

Addition of acetic add must occur with equal probability at the two equivalent carbons of the delocalized ion to give both enantiomers of Aio-2-norbornyl acetate (Fig. 21.54). 

WORKED PROBLEM 21.25 Explain the formation of A o-2-norbornyl acetate from the following reaction ... 

Quadricyclane is a highly strained and reactive compound. It reacts readily with acetic acid to give a mixture of nortricyclyl acetate and exo-norbornyl acetate and with bromine to yield a mixture of 2,6-dibromonortricyclene and exo-5-anti-l-dihvo-monorbornene.3 Quadricyclane undergoes cycloaddition reactions with a variety of dienophiles to give 1 1 adducts.15 1 2 3 4 5 6 7... 

Despeyroux, D. Cole, R. B. Tabet, J. C. Ion-molecule reactions in the gas phase. XVIII. Nucleophilic substitution of diastereomeric norborneols, norbornyl acetates and benzoates under ammonia chemical ionization, Org. Mass Spectrom. 1992, 27, 300-308. 

The first laboratory test of these predictions was the pyrolysis of deuterated ennorbornyl acetate 122. Thus, as predicted by the orbital symmetry rules, this thermal suprafacial [l,3]-sigmatropic reaction took place with complete inversion at C-7. Similar results have been obtained in a number of other cases. However, similar studies of the pyrolysis of the parent hydrocarbon of 121, labeled with D at C-6 and C-7, showed that while most of the product was formed with inversion at... 

Figure 28.9. Conversion of optically active e c< -norbornyl brosylate into racemic x( >norbornyl acetate via nonclassical ion. Brosylate anion is lost with anchimeric assistance from C-6, to give bridged cation III. Cation III undergoes back-side attack at either C-2 (path a) or C-1 (path b). Attacks a and b are equally likely, and give racemic product.

Corey and Casanova found that oxidation of either meso- or dM, 2-diphenyl-succinic acid with lead tetraacetate in pyridine afforded tranr-stilbene (40-45% yield) cw-stilbene was shown not to be an intermediate. Similar oxidation of either endo- or exo-norbornane-2-carboxylic acid gave cjco-norbornyl acetate (24-67%). 

The endo isomer is postulated to be stereoelectronically unfavorable for such participation. Consequently, ionization proceeds with weak solvent participation (8) to give an intermediate (16) which largely (92 to 93%) is converted into the nonclassical species (15) before it reacts with solvent to form product (12). According to this interpretation, only a small amount (7 to 8%) of the intermediate 16 is converted into the optically active eto-norbornyl acetate prior to conversion to 15. 

CJglycerol trinitrate On the other hand, equimolar amounts of H CHO reacted with nitromethane to give 2-nitro[l- C]ethanol (115). Dehydration of 115 furnished 1-nitro-[2- C]ethylene (116). a valuable Michael acceptor and Diels-Alder dienophile. Its reaction with cyclopentadiene, for example, gave predominantly e t/o-2-nitro[3- C]-norcamphane (117). Subsequent catalytic reduction of the double bond, Fe-reduction of the nitro group and concluding acyloxy-deamination converted 117 into exo-[ C]norbornyl acetate (118). ... 

Before we turn to other investigations of the stabilized ion it is interesting briefly to compare the rates of hydride shifts found in the strong acid systems with rates obtained under solvolytic conditions. Collins and Lietzke (1967) and Berson et al. (1967) have deduced the rates of 3,2- and 6,2-hydrogen migration relative to the rate of solvent capture for norbornyl ions in acetic acid, formic acid and other common solvents from elaborate C scrambling studies due to Roberts and Lee (1951) and Roberts et al., (1954) and tritium labelling studies of Lee and Lam (1966). From the ratio of these... 

If the norbornyl cation is formed on solvolysis of < xo-norbornyl derivatives, C2 should become equivalent to C and C7 to C3. In a most elegant tracer experiment, Roberts and Lee synthesized w-2-norbornyl-[2,3-14C] brosylate (85), solvolyzed it in acetic acid, and degraded the product. Equation 6.39 shows the product distribution expected if the symmetrical carbonium ion (82) were formed. The label was found not only at Cx, C2, C3, and C7, but also at C5 and... 

Sodium amalgam reduction of organomercurials in alkaline deuterium oxide gives products with stereospecific retention during the replacement of mercury by deuterium [71]. This was shown in the reduction of cw-8-acetoxymercuri- (Ila) and c75-8-chloromer-curidibenzobicylo[2.2.2]octadien-7-ol acetates (Ilb), /ra/75-8-chloromercuridibenzobicy-clo[2.2.2]octadien-7-ol, and some norbornyl derivatives. Reduction of these compounds with sodium borodeuteride gave products without stereospecific deuterium incorporation [71]. 

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