3- Nortricyclyl radicals

The interconversion of norbornaneyl and nortricyclyl radicals is very rapid, with the latter radical being favored. Therefore, the majority of free radical additions to 2,5-norbornadiene (X = Br) yield mainly tricyclic products and limited amounts of the 1,2-adduct. When the addend is an extremely reactive chain transfer agent (X = I), the 1,2-adduct is the predominant product. 

Further examples of the norbornenyl-nortricyclyl radical rearrangement used as a free radical probe will be discussed in Section Other... 

The radical cations 15 + and 16 + add methanol exclusively from the exo face forming exo-methoxynorbornyl and nortricyclyl free radicals, which undergo rapid cyclopropylcarbinyl-butenyl interconversions (119 120 121 see... 

The bifunctional ferrocene derivative fc(SH)2 has been tested as a component in the synthesis of macromolecules [84, 93, 94]. However, the reaction (1 1) of fc(SH)2 with norbornadiene (in the presence of AIBN) leads to oligomers containing only disulfide-bridged ferrocene units in the main chain [93,95] the diolefin appears solely in the form of norbornenyl or nortricyclyl terminations (Scheme 5-18). The preferred formation of disulfide linkages can be explained by the stability of the ferrocenyl thiyl radicals (Fc-S ), which live long enough to terminate the chain growth by radical combination [94]. 

In certain polycyclic radicals favorable molecular architecture shifts the position of the equilibrium towards the cyclized form, e.g. in the tricyclo[2.2.1.0 ]hept-3-yl (nortricyclyl,31) to bicyclo[2.2.1jhept-2-en-5-yl (norbornenyl, 32) radical rearrangement. In this case the forward and reverse rates are about the same, so the product mixture depends critically on the nature and concentration of the reaction partner." ... 

The product radical undergoes the norbornenyl-nortricyclyl rearrangement. 

A very important and much studied case of intramolecular addition of a 3-butenyl radical is that of the special case 18 this gives high yields of cyclized (Cy 3) products (the so-called norbornenyl-nortricyclyl rearrange-This subject has been extensively covered by Wilt and will be not discussed here except for new results of particular relevance. 

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