Silyl radical with unsaturated bonds

Bromination. In bromolactamization of unsaturated Al-Boc amides with NBS in THF, adding the base r-BuOLi is recommended/ a-Bromo enones are formed by treatment of enol silyl ethers with NBS under uv irradiation and in the presence of a free radical initiator (AIBN)/ The allylic position of an ordinary double bond, being less reactive, remains unaffected. 

Si-H or >Si D bonds in the radical. Silyl radicals add to unsaturated >C0 compounds regioselectiwely, then undergo 1,3-C to 0 silicon migrations, but with 2,6-Du 2 B" 2oquinone, two sets of products form, with addition at... 

We also observed similar phenomena in the reaction of silyl enol ethers with cation radicals derived from allylic sulfides. For example, oxidation of allyl phenyl sulfide (3) with ammonium hexanitratocerate (CAN) in the presence of silyl enol ether 4 gave a-phenylthio-Y,5-un-saturated ketone 5. In this reaction, silyl enol ether 4 reacts with cation radical of allyl phenyl sulfide CR3 to give sulfonium intermediate C3, and successive deprotonation and [2,3]-Wittig rearrangement affords a-phenylthio-Y,6-unsaturated ketone 5 (Scheme 2). Direct carbon-carbon bond formation is so difficult that nucleophiles attack the heteroatom of the cation radicals. 

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