Silanes ketones reduced

Tris(trimethylsilyl)silane (TTMSS) reducing agent for alkyl halides, ketones an alternative to tributyltin hydride. 

Silanes normally reduce aldehydes or ketones under catalytic conditions to the silyl ethers. However, with certain catalysts such as nickel sulfide,Co2(CO)8, or (Ph3P)3RhCl, carbonyl compounds react with silanes to yield an equilibrium mixture of enol silyl ethers (Scheme 17). In a similar vein, the silyl-hydroformylation reaction of cycloalkenes with CO and silanes may be a practical way to prepare enol silyl ethers. An example is the preparation of compound (49). Catalytic 1,4-hydrosilation of a, -un-saturated ketones or aldehydes gives the corresponding enol silyl ethers. The reaction is similar to the reductive silylation referred to previously, but the reaction conditions are neutral and milder. The formation of the enol silyl ether (50) is outlined below. ... 

Dimethyl(phenyl)silane will reduce aldehydes and ketones to hydroxyl compounds under very mild conditions in the presence of a catalytic amount of TASF(Et). ... 

In some transformations, the choice of solvent represents a powerful adjuster bolt for the stereochemical outcome of the reaction. Divergent stereoselectivity in the reduction of glycid ketones 131 is observed when either diethyl ether or HMPA was used with trimethoxy silane as reducing reagent in the presence of catalytic amounts of lithium methoxide (Table 3.2) [49]. Highly coordinated silicon compounds show specific reactivities in comparison to tetra-coordinated silicon compounds [50]. 

Silanes And Base. In the presence of bases, certain silanes can selectively reduce carbonyls. Epoxy-ketones are reduced to epoxy-alcohols, for example with (MeO)3SiH and LiOMe. ° Controlling temperature and solvent leads to different ratios of syn- and anti- products.Silanes reduce ketones in the presence of BF3-OEt2 ° and transition metal compounds catalyze this reduction. ... 

It has been known since 1954 that aldehydes or ketones are reduced by silanes to give silylated primary or secondary alcohols [41]. Reduction of ahphatic aide-... 

Copper-catalyzed systems have been developed that reduce ketones directly to silyl ethers. The reactions involve chiral biphenyl diphosphine type ligands and silane or siloxane hydride donors.187... 

The quininium and quinidinium fluoride catalysts, 10 (R=H etc., X=F) and 8 (R=H, X=F), were used for the asymmetric reduction of alkyl aryl ketones in conjunction with silanes.1751 One of the most efficient silanes proved to be tris(trimethylsiloxy)silane, which together with 8 (R=H, X=F) reduced acetophenone to give the alcohol 102 in almost quantitative yield with 78 % ee, as shown in Scheme 31. The... 

The reduction of a,p-unsaturated ketones is equally fast and remarkably selective for 1,2-addition of the silane. A variety of both cyclic and acyclic a,p-unsaturated ketones were reduced with diphenylsilane under the standard conditions with yields ranging from 66-99% for 1,2-addition. Cyclic enones were reduced with a higher degree of regioselectivity than the acyclic enone, mesityl oxide. 

To a suspension of KF (0.19 g,2.0 mmol) in DMI (10 ml) was added difluoro(ethyl) (4-methylphenyl)silane (0.56 g, 3.0 mmol) under 1 atm of carbon monoxide (balloon). After stirring at room temperature for 10 min, the reaction mixture was heated at 100 °C for 3 h. Bulk of the solvent and the catalyst were removed by passing the mixture through a silica gel column with ethyl acetate-hexane = 1 10 as an eluent solvent. Evaporation of the solvent under reduced pressure afforded 4-acetylphenyl 4-methylphenyl ketone (0.43 g, 91% yield) as a colorless solid. 

Silanes (H2SiPh2) also reduce" ketones asymmetrically in the presence of the chiral catalyst 6.65. 

Hypervalent silicon componnds have found wide utility in organic synthesis. In general, pentacoordinated anionic silicates are more reactive toward nucleophiles than are tetracoordinated silanes. For example, Mes2SiF2 is nmeactive toward water, while (the 18-crown-6 potassium salt of) Mes2SiF3 is completely hydrolyzed within minutes. Similarly, the pentacoordinate anion HSi(OEt)4 is an effective reducing agent for aldehydes, ketones, and esters at or below room temperature (Scheme 2) no snch reaction occurs with HSi(OEt)3. The difference in relative reactivities of hypervalent and nonhypervalent species is relevant to the intermediates proposed in Section 7.6. 

Nucleophilic addition to less reactive ketone carbonyls by Lewis acid activation is also possible. Evans and co-workers have reported enol silane addition to pyruvate esters mediated by chiral copper Lewis acids (Sch. 36) [72]. The aldol reactions proceed with high facial selectivity to provide the tertiary alcohol products 153. The chemical efficiency is, however, reduced when a bulky alkyl group is present at the ketone carbonyl. Addition of more functionalized enol silanes (155) to keto esters enables the establishment of two contiguous chiral centers, a substitution pattern present in a variety of natural products. The stereochemistry of the major product is syn, irrespective of the enol silane geometry. Once again, bidentate coordination of the substrate to the Lewis acid was essential for obtaining high selectivity. 

The reaction of conjugated enones and dienones with trimethyl- and triethyl-silane in the presence of TiCU, followed by aqueous work-up produces the corresponding saturated ketones. This Lewis acid catalysis is particularly useful for conjugated reduction of sterically hindered systems (Scheme 46). " a,p-Unsaturated esters are not reduced under these conditions. 

Silanes. In the presence of bases, certain silanes can selectively reduce carbonyls. Epoxy-ketones are reduced to epoxy-alcohols, for example, with... 

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