Hydrogen peroxide silylated

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 ... 

Immobilized enzymes, 3 670 10 270-272 industrial-scale apphcations of, 10 272 silylating agents and, 22 700—701 Immobilized glucose oxidase, hydrogen peroxide biogeneration for bleaching, 4 65-66... 

Carboxylic peroxides are long known and have been extensively employed in mechanistic and preparative applications. This is also valid for acyclic silyl peroxides, particularly the recently much used BTSP, which as a protected H2O2 exhibits marked advantages as oxidizing agent compared to the parent hydrogen peroxide. 

Treatment of the silyl compound, 61, above with hydrogen peroxide leads to the diol 62 which formally constitutes an oxidation as well as an electrophilic attack on the carbon atom. Classically, oxidation of nonconjugated rings to furnish their conjugated (usually aromatic) analogues is achieved by treatment with nickel(ii) peroxide however, these reactions are common and have been extensively explored for a number of different heterocyclic systems in both GHEC(1984) and CHEC-II(1996) so are not discussed further here. 

Yttrium-catalyzed diene cyclization/hydrosilylation was applied to the synthesis of aliphatic nitrogen heterocycles such as the indolizidine alkaloid ( )-epilupinine. l-Allyl-2-vinylpiperidine 30 was synthesized in four steps in 59% overall yield from commercially available ( )-2-piperidinemethanol (Scheme 10). Treatment of 30 with phenylsilane and a catalytic amount of Gp 2YGH3(THF) gave silylated quinolizidine derivative 31 in 84% yield, resulting from selective hydrometallation of the A-allyl G=G bond in preference to the exocyclic vinylic G=G bond. Oxidation of the crude reaction mixture with tert-huVf hydrogen peroxide and potassium hydride gave (i)-epilupinine in 51-62% yield from 30 (Scheme 10). 

Oxidation of an a-silyl selenide with hydrogen peroxide leads to an aldehyde, silanol and selenol as the primary products [253]. Evidently, the fragmentation proceeds only after contrapolarization at Se, the intermediate now having an a-d-a array. 

A simple example involves the reaction of the silyl ether 213, made from the corresponding 4-hydroxy-alkene by treatment with (bromomethyl)chloro-dimethylsilane, with tributyltin hydride and a radical initiator. Bromine abstraction and intramolecular cyclization with the double bond leads to the bicyclic 214, which upon oxidation with hydrogen peroxide gives the branched-chain 215 in an overall yield of 73% from the alcohol precursor of 213 (Scheme 21). When the sequence is conducted with the C-4 epimeric starting alcohol, the final product again has the hydroxymethyl group cis-related to the hydroxy group.217... 

Eq. 3.21 shows the introduction of a hydroxymethyl group at the (3-position of allylic alcohol with the silicon-tethered radical approach developed by Stork [78-83]. Allyl silyl ether (64) was first prepared by the treatment of allylic alcohol (63) with dimethylbromomethylsiliyl chloride, and subsequently treated with Bu3SnH/AIBN, and finally treated with hydrogen peroxide in the presence of KF, to give a 1,3-diol derivative (66), as shown in eq. 3.21. 

Several replacement reactions at C-4 in sydnones may be carried out but aqueous bases must be avoided. Butyllithium can be used to displace bromine from a 3-phenylsydnone the resulting organolithium salt can be carbonylated, will add to ketones, and forms a silyl derivative (80CB1830). A sydnone Grignard derivative can also be made and will add ketones in the normal way (80JCS(Pl)20). Sodium borohydride will reduce a sydnone sulfone, formed by oxidation of a thioether (Table 5) with hydrogen peroxide, back to the unsubstituted sydnone (74T409). 

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