Carbon-silicon bonds oxidative cleavage

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). 

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. 

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. 

Tamao, K., Hayashi, T., Ito, Y. Oxidative cleavage of carbon-silicon bonds by dioxygen catalysis by a flavin-dihydronicotinamide redox system. J. Chem. Soc., Chem. Commun. 1988, 795-797. 

The Lewis acid-promoted reaction of aldehydes with a-substituted allylsilanes affords 3-silyltetrahydrofurans, in good to high yields, with homoallyl alcohols [476-479]. The use of homochiral a-substituted allyl- and crotyldimethylphenylsilanes realizes highly diastereo- and enantioselective syntheses of tri- and tetrasubsti-tuted THF derivatives, which can be converted into 3-hydroxy-THF derivatives by oxidative cleavage of the carbon-silicon bond (Scheme 10.171) [476-478]. 

High regio- and stereo-controlled synthesis of 1,3-diols is effected through the intramolecular hydrosiiyiation of chiral allylic and homoallylic alcohols followed by oxidative cleavage of the carbon-silicon bond. This method consists of (1) the silylation of... 

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 ... 

Yoshida J, Murata T, Isoe S (1986) Electrochemical oxidation of organosihcon compounds 1. Oxidative cleavage of carbon-silicon bond in allylsilanes and benzylsilanes. Tetrahedron Lett 27 3373-3376... 

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. 

An interesting application of the cydization of alkenyl thioacetals is the stereoselective preparation of olefmic diols. Thus, oxidative cleavage of the silicon—carbon bond [32] in the ring-closed metathesis products, i.e. cyclic allylsilanes such as 35 and 36, affords (Z)-alk-2-ene-1,5-diols 37 and 38 (Scheme 14.18) [33],... 

Suda and coworkers described the anodic oxidation of 2-silyl-l,3-dithianes which have two sulfur atoms on the carbon adjacent to silicon [42], In this case, however, the C Si bond is not cleaved, but the C-S bonds are cleaved to give the corresponding acylsilanes (Scheme 12). Although the detailed mechanism has not been clarified as yet, the difference in the anode material seems to be responsible for the different pathway of the reaction. In fact, a platinum plate anode is used in this reaction, although a carbon anode is usually used for the oxidative cleavage of the C-Si bond. In the anodic oxidation of 2-silyl-l,3-dithianes the use of a carbon anode results in a significant decrease in the yield of acylsilanes. The effects of the nature of the solvent and the supporting electrolyte may also be important for the fate of the initially formed cation radical intermediate. Since various 2-alkyl-2-silyl-l,3-dithianes can be readily synthesized, this reaction provides a convenient route to acylsilanes. 

Decamethylsilicocene (82) can be regarded as an electron-rich silicon(II) compound containing a hypercoordinated silicon atom. The chemistry of 82 is determined by (a) the nucleophilicity of the silicon lone-pair (cr-donor function towards electrophiles, oxidative-addition processes) and (b) the weakness of the silicon-(cyclopentadienyl)carbon jr-bond rearrangement, Si—C bond cleavage). In the following section, the chem-... 

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