Fragmentation initiator-derived radicals

Trifluoromethylation of pyrrole (and indole and imidazole) occurs on irradiation of a mixture of the compound with difluorodiiodomethane, again via a SET mechanism involving fragmentation of the radical anion (Scheme 31). The presence of the CF3 group in the final products, 45 and 46, is a result either of secondary decomposition of the initially formed—but not isolated—difluoroiodomethyl derivatives, or of formation of the CF3 anion or radical in situ [94], Perfluoroalkyla-tion of pyrroles can also be achieved by an SrnI mechanism—by reaction with perfluoroalkyl iodides in the presence of magnesium or zinc [95]. Indole, on the other hand, gives a mixture of the seven possible alkylated derivatives when irradiated in the presence of ethyl chloroacetate [96],... 

The complex photochemistry of cysteine derivatives sensitized by 4-carboxy-benzophenone 15 has been unravelled by CIDNP. The initially formed sulphur-centred (see. Figure 19) radical decarboxylates rapidly to give an a-amino alkyl radical, which in turn cleaves into a thiyl radical R-S and a vinylamine in competition with being oxidized to an imine by surplus sensitizer all these resulting species are unstable themselves and undergo further reactions. The rates of the radical fragmentations and the radical oxidation were obtained from the CIDNP experiments. 

These radical polymerizations may simply be considered as an insertion of monomer molecules into the R-R bond of the initiator leading to the polymer with two initiator fragments. Thus, the end groups of the polymer are controlled by the initiator used. Otsu proposed the name iniferter (im tiator-trans/er agent-terminator) for the initiators with such functions [64]. Many radical initiators, such as peroxides, azo compounds, tetraphenylethane derivatives, and organic sulfur compounds, may be expected to serve as an iniferter, if monomers and polymerization conditions are selected. Some peroxides show relatively high... 

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