Brook radical

Davies, K.J.A., Quintanilha, A.T., Brooks, G.A. and Packer, L. (1982). Free radicals and tissue damage produced by exercise. Biochem. Biophys. Res. Commun. 107, 1198-1205. 

It is worth mentioning that in a few cases the (3-elimination of the silyl radical from the a-silyl alkoxyl radical (47) with the formation of corresponding carbonyl derivative was observed [63,64]. Evidently the fate of a-silyl alkoxyl radical depends on the method of radical generation and/or the nature of the substrate. Two examples that delineate the potentialities of this rearrangements are reported in Reactions (5.33) and (5.34). In the former, the 5-exo cyclization of secondary alkyl radical on the carbonyl moiety followed by the radical Brook rearrangement afforded the cyclopentyl silyl ether [65], whereas Reaction (5.34) shows the treatment of an a-silyl alcohol with lead tetracetate to afford the mixed acetyl silyl acetal under mild conditions [63]. 

The addition of (TMS SiH across carbon-carbon multiple bonds under free-radical conditions is well documented82. Although no recent reports of such hydrosilylation processes are reported, the addition of (TMS Si radical to multiple bonds, followed by other radical reactions, were investigated (vide infra). The hydrosilylation of ketones and aldehydes is also well known83. In this respect Brook and coworkers have recently shown that the (TMS)3Si group can be used for the protection of primary and secondary alcohols84. 

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... 

Tsai and coworkers89,91,246,247 reported the synthesis of cyclic silyl enol ethers and silyl ethers by using a radical cyclization followed by the radical Brook rearrangement (equation 111). The cyclization of 4-bromo-4-stannylbutyl silyl ketones 188 in benzene with a catalytic amount of tributyltin hydride and AIBN gave cyclic silyl enol ethers 18989 91 247. The whole catalytic cycle proposed is shown in equation 112. 

The dimerization of the transient silenes 2a-2c is discussed in terms of a radical process, which was proved by Brook et al. for some similarly structured 2-alkyl- and 2-phenyl-2-trimethylsiloxy-l,l-... 

Wamcke, K., Brooks, H. B., Lee, H.-L, McCracken, J. L., Davidson, V. L., and Babcock, G. T., 1995, Stmcture of the dithionite-generated tryptophan tryptophylquinone cofactor radical in methylamine dehydrogenase revealed by ENDOR and ESEEM spectroscopies, J. Am. Chem. Soc. 117 10063nl0075. 

Numerical solutions have also been obtained by Brooks (1980) using his three-state model (see above). The relevant simultaneous differential equations were solved Euler s method. Brooks has included in his examples the case where o decays exponentially with time. In all the cases investigated. he finds that allowance must be made for bimolecular mutnal termination of radicals and for the re-entry of desorbed radicals into reaction loci he concludes that failure to take account of these possibilities can lead to serious errors. 

Paredes, M. D., Alonso, R. On the Radical Brook Rearrangement. Reactivity of a-Silyl Alcohols, a-Silyl Alcohol Nitrite Esters, and (i-Haloacylsilanes under Radical-Forming Conditions. J. Org. Chem. 2000, 65, 2292-2304. 

Schiesser, C. H., Styles, M. L. On the radical Brook and related reactions an ab initio study of some (1,2)-silyl, germyl and stannyl translocations. J. Chem. Soc., Perkin Trans. 2 1997, 2335-2340. 

Acylsilanes also function as intramolecular radical acceptors, but, interestingly, a radical-Brook rearrangement takes place to give the silylated cycloalkanols (Scheme 4-20) [40]. 

Radical Addition Followed by Brook-type Rearrangement... 

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