Siloxyalkyl radicals

In addition to the radical Brook rearrangement from a-silylalkoxy radical 45 to the siloxyalkyl radical 46 shown in equation 37, several 1,2-silyl migrations to a radical... 

The a-siloxyalkyl radical intermediate can be used for carbon-carbon bond formation by intra- and intermolecular trapping (Scheme 10.233). In the BUjSriH-mediated system, a bromoalkenoylsilane is efficiently converted into a bicyclic compound by tandem radical cyclization [601]. When allyltributylstannane is used instead of BuaSnH, the a-siloxyalkyl radical generated from a 5-bromoalkanoylsi-lane undergoes homolytic allylation to provide a homoallyl silyl ether [602]. 

Radical cyclization using acylsilanes is apphcable to the synthesis of cychc silyl enolates by yS-elimination of the a-siloxyalkyl radical intermediate (Scheme 10.234) [603]. 5-Bromo-5-stannyl- and 5-bromo-2-sulfonyl-alkanoylsilanes are cychzed to cyclopentanone silyl enolates with ehmination of the stannyl and sulfonyl groups. 

In a similar case, hydrosilylation of a 1,6-diene or 5-en-l-one with tris(trimethylsilyl)silane gives the cyclized products with a preferred as orientation of the alkyl groups7. The intermediate silylalkyl or siloxyalkyl radical, respectively, is trapped intramolecularly to give substituted cyclopentanes. 

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