Benzene reductive silylation

Closely related to the Birch reduction, benzene, and other aromatic compounds afforded reduction-silylation products (equation 10). Electron-transfer reactions of bis(phenylethynyl)dimethylsilane gives 2,5-dianion of 3,4-diphenylsilole that is a useful intermediate to variously substituted siloles (equation 11). ... 

An interesting alternative to the Birch reduction with useful synthetic potential is provided by reductive silylation. Benzene, on treatment with lithium metal and trimethylsilyl chloride in THF for a pro-... 

Arylsilane radical anions undergo cleavage and coupling reactions, usually under conditions where excess reducing agent is available. Reduction of phenylsilane, diphenylsilane, or triphenylsilane with sodium-potassium alloy under preparative conditions gives high yields of tetraphenylsilane (7). In the reduction of phenylsilanes, the appearance of 1,4-bis(silyl)benzene radical anions is frequently observed (135, 35, 86, 97, 75, 120, 100). Typical results are shown in Table II. 

Similar octahedral facial silyl methyl hydride complexes of the type IrL3H(SiR3)Me have been shown to induce competitive C—H/Si—C reductive elimination depending on the electronic properties of the silyl ligand, thus affording a novel example of a metallation of silyl ligands or the metallation of the sp3C—H bond of the ethyl moiety when R = OEt. For the complex with R = Et, mixtures of different complexes are formed by the thermolysis with benzene (Scheme 32)198,199. 

The fluoride ion-induced reductive / -elimination makes it possible to generate highly strained olefins [Eq. (31)]. /J-Silyl A3-iodane 40 generates five-mem-bered cumulene with remarkable reactivity at room temperature and affords Diels-Alder adduct 40a (7 % yield) by the reaction with benzene [63]. 

The silyl halides can now" be prepared in high purity and high yield by the facile hydrogen halide cleavage of the carbon-silicon bond in arylsilanes. " No catalyst is required, and the use of the hazardous intermediate reagent, silane, is avoided. Bromosilane is prepared by the reaction of hydrogen bromide and phenylsilane. The latter is obtained by lithium hydro-aluminate reduction of the commercially available phenyltri-chlorosilane. lodosilane can be prepared in a similar fashion however, mixtures of iodosilane and benzene are difficult to separate. The preferred alternative procedure described below utilizes an isomeric mixture of 2-, 3-, and 4-chlorophenylsilanes as the intermediate. This intermediate is obtained by the chlorination of phenyltrichlorosilane, and is then reduced to the hydride. 

A 4-silyl-substituted isoxazolidin-5-one was desilylated by treatment with citric acid <2003S1441>. 4-(Phenylselenyl)isoxazolidines underwent reductive deselenylation by treatment with PhsSnH in the presence of a catalytic amount of AIBN in refluxing benzene <2001TA3053>. 

Mistryukov, E. A. Ultrasound in organic synthesis. Electron-transfer catalysis in Li-TMSCI reductive benzene silylation and TMSCI Wurtz coupling. Mendeleev Common. 1993, 251. 

Although ethyl 3-methylbutanoate on reduction with sodium in the presence of TMS-Cl in benzene or ether gives the expected silyl enediol ether (4), in DME or THE the product is the noncoupled product... 

Alkoxy radicals for ring expansion can be generated from alcohols by oxidative methods such as hypohalite thermolysis/photolysis [19a] and lead tetraacetate oxidation [19b], or peroxide reduction [19c]. The recent development of the hyper-valent organoiodine reagent (diacetoxyiodo)benzene (DIB) provides another way for efficient generation of alkoxy radicals (Scheme 11) [19d]. Additional oxidative methods to prepare cyclopropyloxy radicals include reaction of tertiary cyclopropanols or their silyl ether derivatives with various reagents such as manganese(III) tris(pyridine-2-carboxylate) [Mn(pic)3] [20a], Fe(III) salts [20b], and vanadyl ace-tylacetate [20c] (Scheme 12). 

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