Radicals, anti-Markovnikov dimerization

Dimer formation can be quenched by conducting the experiment in a nucleophilic solvent, and the product obtained is characteristic of radical cation trapping. The anti-Markovnikov addition of acetone across the C-C single bond of the methylated analogue, eq. 41 (116,117),... 

When electron transfer reactions of olefins are carried out in nucleophilic solvents (alcohols) or in the presence of an ionic nucleophile (KCN/acetonitrile/2,2,2-trifluoroethanol), the major products formed are derived by anti-Markovnikov addition of the nucleophile to the olefin. In several cases, nucleophilic capture completely suppresses dimer formation [122, 143]. It is important to realize that the observed mode of addition reflects the formation of the more stable (allylic) intermediate and cannot be interpreted as evidence for the charge density distribution in the radical cation. 

The best experimental conditions to introduce a phenylseleno and an azido group to the alkene double bond are those which employ diphenyl diselenide, sodium azide and iodobenzene diacetate in methylene chloride. Under these conditions, however, the addition reaction occurs through the radical mechanism illustrated in Scheme 12 [581. The addition therefore occurs with an anti Markovnikov orientation and it is not stereospecific. The reaction is initiated by the oxidation of the azido anion to the azido radical, which adds to the alkene to afford a carbon radical. This is trapped by the PhSeSePh to afford the final product and a PhSe radical, which dimerizes to give the diselenide. 

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See also in sourсe #XX -- [ , ]

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