Reaction with hydroxy-bearing radicals

Simple alkyl radicals such as methyl are considered to be nonnucleophilic. Methyl radicals are somewhat more reactive toward alkenes bearing electron-withdrawing substituents than towards those with electron-releasing substituents. However, much of this effect can be attributed to the stabilizing effect that these substiments have on the product radical. There is a strong correlation of reaction rate with the overall exothermicity of the reaction. Hydroxymethyl and 2-hydroxy-2-propyl radicals show nucleophilic character. The hydroxymethyl radical shows a slightly enhanced reactivity toward acrylonitrile and acrolein, but a sharply decreased reactivity toward ethyl vinyl ether. Table 12.9 gives some of the reactivity data. 

Nitroxide attached to macromolecules also induces the living radical polymerization of St. Yoshida and Sugita [252] prepared a polymeric stable radical by the reaction of the living end of the polytetrahydrofuran prepared by cationic polymerization with 4-hydroxy-TEMPO and studied the living radical polymerization of St with the nitroxide-bearing polytetrahydrofuran chain. The nitroxides attached to the dendrimer have been synthesized (Eq. 69) to yield block copolymers consisting of a dendrimer and a linear polymer [250,253]. 

Similar reactions were performed with dioxolanes 400 bearing abstractable hydrogen atoms in the 2-position (Fig. 93) [436]. Radical addition to acceptors 401 and oxygenation gave protected 2-hydroxy-4-oxo carbonyl compounds 402 in 16-84% yield. For these substrates a catalyst system of 0.1 mol% Co(OAc)2 and 5 mol% 398 proved to be sufficient to achieve good yields. Low yields were only obtained with (i-alkyl-substituted substrates 401. Methyl vinyl ketone undergoes a fragmentation under the reaction conditions. 

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