Bond cleavage carbon-silicon

Trimethylsilylbutadiene 140 is treated with acetyl chloride at — 80 °C to give the adducts, which are dehydrochlorinated to give 141 (equation 117)209. No carbon-silicon bond cleavage is observed. 

Carbon-silicon bond cleavage is an important reaction in organosilane chemistry. 

The corresponding inter-and intra-raolecular additions of allyl-silanes to iminium salts give rise after desilylation to synthetically useful biradical intermediates. Evidence for the existence of two mechanisms for such reactions, differing only in the timing of carbon-silicon bond cleavage and carbon-carbon bond formation, has been described. Analogous electron transfer... 

The reaction of 1 -trimethylsilylnaphthalene with pivaldehyde in the presence of 20 mol% Bu-P4 base proceeded smoothly at room temperature to give the alcohol in 91% yield. Other phosphazene bases with weaker basicities, such as Bu-P2 base and BEMP, showed no catalytic activity. As one of the conventional strong organic bases, DBU was found to be inactive. Caesium fluoride (CsF) was then examined as a fluoride anion donor, but no carbon-silicon bond cleavage was observed. Reactions with other aldehydes have been examined that with benzaldehyde was found to proceed somewhat slowly at room temperature. Other aryl aldehydes with electron-donating groups were also employed as electrophiles and the reactions proceeded smoothly at room temperature [57] (Table 5.5). 

Benzylic silanes bearing an electron-donating group experience an oxidative carbon-silicon bond cleavage selectively with oxovanadium(V) compounds to permit an intermolecular carbon-carbon bond formation the addition of TMSOTf resulted in a more facile coupling (eq 123)4 ... 

Pudelski JM, Manners I (1995) A heterolytic cyclopentadienyl carbon-silicon bond cleavage mechanism for the thermal ring-opening polymerization of silicon-bridged [l]ferroceno-phanes. J Am Chem Soc 117 7265-7266... 

The selective carbon-silicon bond cleavage is of synthetic potential. Oxidative carbon-silicon bond cleavage is similarly achieved through oxovanadiumfV)-induced one-electron oxidation. The carbon-silicon bond of the dihydrofuran, which is obtained by the VO(OR)Cl2-induced cyclization of diketene with a-trimethylsilylstyrene is oxidatively cleaved by using VO(OEt)Cl2-Me3SiOTf, to give the furan [125]. 

Primary alcohols are available in good yields from terminal alkenes via the organopentafluorosilicate adducts (1) and a novel oxidative carbon-silicon bond cleavage using peracid (Scheme 2) This latter reaction is very medium-dependent DMF was found to be the solvent of choice. 

This excellent method of oxidative cleavage (/) of carbon-silicon bonds requires that the silane carry an electronegative substituent (2), such as alkoxy or fluoro. Either hydrogen peroxide or mcpba may be used as oxidant, and the alcohol is produced with retention of configuration (3). Fluoride ion is normally a mandatory additive in what is believed to be a fluoride ion-assisted rearrangement of a silyl peroxide, as shown below ... 

Catalytic asymmetric hydrosilylation of prochiral olefins has become an interesting area in synthetic organic chemistry since the first successful conversion of alkyl-substituted terminal olefins to optically active secondary alcohols (>94% ee) by palladium-catalyzed asymmetric hydrosilylation in the presence of chiral monodentate phosphine ligand (MOP, 20). The introduced silyl group can be converted to alcohol via oxidative cleavage of the carbon-silicon bond (Scheme 8-8).27... 

The use of a silyl ether temporary linkage introduced by Nishiyama [82J and Stork [77,83] allows the facile cleavage of the five-membered ring formed in the cyclization by oxidation of the carbon-silicon bond. This procedure has been successfully used for the hydroxymethylation of sugars at position 3, 4, and 6 [84-86] (Scheme 24). 

Compounds containing only one silicon atom (or, in a few cases, where there is more than one silicon atom but where they are separated from each other by carbon atoms and so behave as a single silicon atom) where the photochemistry observed normally involves cleavage (usually homolytically) of a carbon-silicon bond. 

Reductive cleavage of the carbon-silicon bond of acyl silanes, including a-alkoxy and t/./i-dialkoxy derivatives, to give aldehydes may be accomplished by palladium-catalysed hydrogenolysis at ambient temperature and pressure212. 

Oxidative cleavage of the carbon-silicon bond has been the subject of a recent and comprehensive review119, in which emphasis has been placed on the compatibility of the oxidation conditions with various functional groups, with the inclusion of very useful compatibility tables. 

A. Coupling Reactions Involving the Cleavage of the Carbon—Silicon Bond... 

Exhaustive cleavage of the carbon-silicon bond followed by treatment with an acid converted the complex benzo[f]furan 261 to phenol 262, as illustrated in Equation (154) <2003JA12994>. Villeneuve and Tam were able to interrupt this phenol formation by choosing Cp"Ru(COD)Cl as the catalyst. Thus, the reaction of 1,4-epoxy-1,4-dihydronaphthalene 263 with a ruthenium catalyst in 1,2-dichloroethane at 60 °C afforded the 1,2-naphthalene oxide 264 (Equation 155) <2006JA3514>. 

This chapter concentrates on those processes in which oxidative cleavage of a carbon-silicon bond results in pr uction of the alkyl/aiyl fragment as an alcdiol henol. Other cleavage processes are dealt with, but more briefly. 

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. 

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