Cyclobutyl radicals oxidation

Thus the first electron transfer to Pb relates to the reaction (a) in Section 7.4.3.1.1, and the second involves the oxidation of the cyclobutyl radicals either by electron transfer/deprotonation with Cu" in equation (17) or by ligand transfer of chlorine with PlAci in equation (18). When the product of a generic reaction is itself a radical cation (such as in Sections 7.4.3.1.8 and 7.4.3.1.9), an electron-transfer chain or ETC process can ensue, as in the hole-catalyzed cycloadditions and autoxidations of dienes,The electron-transfer propagation sequence for the latter is simply given as in equations (19) and (20). 

In many cases, particularly for the study of fast reactions (ky> key in Scheme 164), the opening of the cyclopropylmethyl radical to the isomeric allyl-carbinyl radical, one thousand times faster than the cyclization of the 5-hexenyl radical, is a useful complementary tool. It has been used mainly by Kochi for the study of cage reactions of alkyl radicals in solution as well for the study of ligand and electron transfer oxidations of alkyl radicals. Furthermore, in the last three studies the knowledge of the fate of the isomeric cyclobutyl intermediate was very useful in distinguishing between a homolytic (no rearrangement of the cyclobutyl radical) and a heterolytic pathway (fast... 

The oxidation of cyclobutanemethanol and a,a-dimethylcyclobutanemethanol with lead tetra-acetate in benzene gave the same product distributions within the isomeric homoallylic, cyclobutyl and cyclopropylmethyl actates. The distribution was the same in the oxidation of cyclobutane carboxylic acid, suggesting that alcohol p-cleavage and acid decarboxylation gave rise to the same radical species. 

This process is very fast with = 1, and has been observed in the photolysis of nitrite esters X = NO and the oxidation of cyclopropanols, with a regiochemistry of ring opening which has been compared in terms of frontier molecular orbital theory to the one observed with cyclopropylcarbinyl radicals (Section V.2.B). It is also a fast process with n = 2 as in the oxidation of cyclobutanols, although photolysis of a steroidal cyclobutyl nitrite gives the cyclobutanol in substantial amounts (unexpected), along with products resulting from the )5-scission of the cyclobutanoxyl radical to tertiary and also... 

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