Norbomyl halide

The methods that we worked out in the early 1960 s to generate and observe stable carbocations in low nucleophilicity solutions2 were successfully applied to direct observation of the norbomyl cation. Preparation of the ion by the a route from 2-norbomyl halides, by the jt route from /3-A3-cyclopentenylethyl halides, and by the protonation of nortricyclene all led to the same norbomyl cation. 

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. 

Representative reductions of alkyl halides with LiBEtyH are shown in Table 4. Most alkyl halides, including chlorides, are reduced under mild conditions in essentially quantitative yields. Even hindered alkyl halides, such as neopentyl bromide and cAro-norbomyl bromide, undergo facile reduction to the corresponding alkanes in more than 96% yield with this reagent. 

In summary, 2-norbornyl cations, generated by solvolysis of exo-2-norbornyl halides of sulfonates, behave as symmetrical (achiral) intermediates. Other modes of generation (deamination, hydrogen shifts, addition of HX to norbomene) lead to partial asymmetry, excluding the bridged norbomyl cation as the only intermediate. Although classical 2-norbornyl cations may intervene in some of these reactions, no unequivocal identification has been achieved and alternative interpretations are possible. 

Kropp and coworkers have been concerned with systems in which homolysis is followed by rapid electron transfer, such as the photolysis of certain alkyl halides [55]. Photolysis of the norbomyl phenyl sulfoxide 110 was examined. The notion was that sulfide photolysis is usually homolytic, but the sulfinyl radical is more electronegative than the sulfenyl (thiyl) radical, which might assist in electron transfer reactions. Thus, it was thought, ionic reactivity might be observed. In addition to inversion of the sulfur center and deoxygenation (yide infra), norbomane 111 and norbomene 112, both presumed to... 

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