Norbornyl iodide

Products resulting from photolysis of alkyl iodides indicate that according to Scheme 58 homolysis of the C—bond is followed by electron transfer, which results in an ion pair in a solvent cage (Kropp, 1984). In the case of norbornyl iodide (171) and other bridgehead iodides, bridgehead cations re-... 

By contrast, the 2-norbornyl cation is easily formed. Moreover, the 2-norbornyl system can readily undergo elimination. On irradiation in CH3OH or (CH3)5COH, the 2-norbornyl iodides 64a underwent exo,endo equilibration and afforded the 1,2- and 1,3-elimination products 66 and 67, along with the nucleophilic trapping product 68. > The corresponding bromides 64b each afforded the same products, along with small amounts of the radical products 65 and 9, but underwent no detectable interconversion. 

It would be useful to have ail efficient method for the conversion of the generally cheaper, readily available alkyl chlorides to the more reactive, synthetically useful alkyl bromides and iodides. Ferric bromide and iodide catalyze this reaction but the complete loss of stereochemistry in the bromide exchange with exo-2-norbornyl and cis- and rran.s-4-rerr-butylcydohexyl chlorides reduces its usefulness when stereochemistry is important197. 

Irradiation of bridgehead bromides and iodides (RX) in a variety of solvents (SH) results in the formation predominantly of the nucleophilic substitution products (RS) as well as some hydrocarbon (RH), particularly with the bromides. Both radical and heterolytic cleavage of the photoexcited RX molecules are encompassed within the mechanisms discussed. The systems studied include 1-norbornyl, 1-norbornylmethyl, and 1- and 2-adamantyl bromides and iodides. Electrochemical and metal-ammonia reduction of 1,4-dihalogenonorbornanes yields mainly nor-bornane (and not the required [2,2,l]propellane) and some l,r-bisnorbornane. ... 

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. 

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