Homolytic substitution at silicon

An example of C—Si bond formation concludes this overview of carbon heteroatom bond formation. Reflux of bromide 62 in benzene and in the presence of small amounts of (TMS)3SiH and AIBN afforded the silabicycle 63 in 88 % yield (Reaction 7.64) [76]. The key step for this transformation is the intramolecular homolytic substitution at the central silicon atom, which occurred with a rate constant of 2.4 x 10 s at 80 °C (see also Section 6.4). The reaction has also been extended to the analogous vinyl bromide (Reaction 7.65) [49]. 

Homolytic substitution reactions including homolytic allylation, radical [2,3]-migrations and stereochemical reactions been reviewed. The review also highlights the possible applications of homolytic substitution reactions. ni reactions at silicon (by carbon-centred radicals in the a-position of stannylated silyl ethers) are efficient UMCT reactions producing cyclized alkoxysilanes. Bimolecular reactions can also be facilitated in good yield (Schemes 32 and 33). ... 

The calculations predict that the degenerate homolytic substitution by silyl radical at the silicon atom of disilane proceeds by mechanisms that involve either a back-side or a front-side attack, having similar activation barriers of 12.6 and 13.9 kcalmol-1, respectively. Similar conclusions were obtained for the degenerate homolytic substitution reactions involving GeH3 and SnH3, with barriers of 15.6 kcalmol-1 ( back-side ) and... 

A radical approach to cyclization is offered by the intramolecular homolytic substitution (ShO reaction at a silicon center. Reaction of phenyl bromoacetate with a stannylated silyl homoallyl ether under atom transfer conditions provides cyclic alkoxysilanes (Equation (119)).2... 

In a thorough study on the homolytic substitution reaction at silicon, Studer and Steen reported a mild method for the formation of cyclic five-membered alkoxysilanes based on tandem intermolecular add-ition/intramolecular homolytic substitution [137], whereby the reaction of homoallylic stannylated silylether 149 with ethyl iodoacetate in the presence of (Me3Sn)2 led to the desired Sni product 150 in high yield as the sole trans diastereoisomer (Scheme 49). While the 1,2 induction proved to be very high, leading in some cases to a unique diastereoisomer, 1,3 stereoselectivities were... 

Benzylseleno-l-(2-iodophenyl)ethanol reacts smoothly with tris(trimethylsilyl)silane to give benzo[ ]selenophene (eq 13). A similar homolytic substitution reaction at the silicon atom yields a sila bicycle. ... 

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