Silylmethyl radicals cyclizations

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. 

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. 

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). 

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... 

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