Radical silylmethyl

H. Nishiyama, T. Kitajima, M. Matsumoto, and K. Itoh, Silylmethyl radical cyclization New stereoselective method for 1,3-diol synthesis from allylic alcohols, J. Org. Chem. 49 2298 (1984). 

Silylmethyl radical cyclizations are a related class of reactions in which the heterocycle serves a temporary purpose to direct the introduction of a methyl or hydroxymethyl group adjacent to the hydroxy group. Starting from the optically active allylic decalin alcohol, reaction with bromomethyl(chloro)dimethylsilane gives the a-bromosilyl ether. Treatment with tributyltin hydride affords the stereoselective cyclization to a five-membered siloxane62. The siloxane ring is converted either to the a.r-dihydroxy compound, or to the ot-methylated derivative63. 

In the total synthesis of talaromycin A, silylmethyl radical cyclization serves as a method for the stereoselective introduction of the 1,3-diol unit64. Starting from the corresponding alcohol, silylation, radical cyclization of the (bromomeihyl)dimethylsilyl eLher 4 and subsequent oxidative cleavage gives the desired product in 78% overall yield. 

Aerobic oxidation of trimethylsilylmethylmagnesium chloride in the presence of a-methylstyrene results in addition of trimethyl-silylmethyl radical to the carbon-carbon double bond followed... 

Toyota, M Yamamoto, N Nishikawa, Y, and Fukumoto, K. (1995) Silylmethyl radical cyclization in theopederins synthesis a new access to pederic acid. Heterocycles, 40,115-117. 

Photoinduced electron transfer promoted cyclization reactions of a-silyl-methyl amines have been described by two groups. The group of Pandey cyclized amines of type 135 obtaining pyrrolidines and piperidines 139 in high yields [148]. The cyclization of the a-silylated amine 140 leads to a 1 1 mixture of the isomers 141 and 142 [149]. The absence of diastereoselectivity in comparison to analogous 3-substituted-5-hexenyl radical carbocyclization stereochemistry [9] supports the notion that a reaction pathway via a free radical is unlikely in this photocyclization. The proposed mechanism involves delocalized a-silylmethyl amine radical cations as reactive intermediates. For stereochemical purposes, Pandey has investigated the cyclization reaction of 143, yielding... 

Diols. Intramolecular radical cyclization of the allylic silylmethyl ether 1 followed by oxidation of the Si—C bond with H O, (this volume) results in a 1,3-diol (2). 

Vinyl (or cyclopropyl) silyl ethers have also been used to generate carbon-centered radicals by treatment with CAN. 3,6-Dihydroxyphthalate esters are produced by dimerization when bisenolsilylated 1,3-diketones are treated with CAN. An elegant example is the three-component condensation of cyclopropyl silyl ether, cyclopentenone, and methyl vinyl ether (eq IS). Oxidation of cyclopropyl silyl ether gives the 8-ester radical, which undergoes tandem radical addition processes apparently controlled by electronic effects. Subsequent oxidation and trapping affords the 2,3-disubstituted cyclopen-tanone in an excellent stereoselectivity. Other substrates include tertiary aminocyclopropanes, iV-(silylmethyl)amides, and VUV-dialkylanilines. For example, CAN-mediated oxidation of IVUV-dialkylanilines in water affords the coupling products -tetraalkylbenzidines. ... 

Crosslinked sulfonated poly(imide-siloxane) can be obtained by the radical grafting onto the silylmethyl group of poly(dimethylsiloxane) [59]. Large, well-connected hydrophilic domains have been detected by transmission electron microscopy that are responsible for the high proton conductivity of the membrane. The unique phase separated morphology of the membrane is responsible for the outstanding hydrolytic stability. 

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