Trimethylsilane, reaction

Butyroin has been prepared by reductive condensation of ethyl butyrate with sodium in xylene, or with sodium in the presence of chloro-trimethylsilane. and by reduction of 4,5-octanedlone with sodium l-benzyl-3-carbamoyl-l,4-dihydropyridine-4-sulfinate in the presence of magnesium chloride or with thiophenol in the presence of iron polyphthalocyanine as electron transfer agent.This acyloin has also been obtained by oxidation of (E)-4-octene with potassium permanganate and by reaction of... 

Use of freshly distilled bis(silyloxy) compound is critical in many cases, especially in this example. The yield and, more particularly, the quality of the product deteriorate with the age of the sample. Traces of acid should he avoided because even as little as one drop of chloro-trimethylsilane added to the reaction mixture produces a diflferent product. The longer the reaction time in the presence of acid, the greater is the number of other products formed. 

In order to test whether this high level of diastereoselectivity is due to the stereoselective formation of 35 A, or a consequence of rapid equilibration between 35 A and 35 B, both reagents were selectively prepared via the tributylstannanes 38. Treatment of either reagent with chloro-trimethylsilane led to a similar ratio of the diastereomers 36 A/36B, with the anti-diastereomer 36A predominant in both reactions. 

Similar additions may be performed with the enamine 13. However, with 3-buten-2-one or methyl 2-propenoate Lewis acid catalysis is needed to activate the Michael acceptor chloro-trimethylsilane proved to be best suited for this purpose. A remarkable solvent effect is seen in these reactions. A change from THF to HMPA/toluene (1 1) results in a reversal of the absolute configuration of the product 14, presumably due to a ligand effect of HMPA235. 

Vinylsilanes (Chapter 3) can be readily converted into a/3-epoxysilanes, normally by treatment with mcpba (/). Alternatively, a-chloro-a-lithio-a-trimethylsilanes react efficiently with aldehydes and ketones in a manner reminiscent of the Darzens reaction (2). 

A solution of TMSOTf 20 (3 pL, 0.017 mmol) in 1 mL acetonitrile is added at -20 °C under an argon atmosphere to a solution of benzaldehyde dimethyl acetal 121 (0.34 mmol, 51.7 mg) and (Z)-(5-trimethylsilyloxy-2-pentenyl)trimethylsilane 640 (94.9 mg, 0.412 mmol) in 3 mL acetonitrile. After 20 min at 20 °C the reaction is quenched with phosphate buffer (pH 7). The combined CH2CI2 extracts are washed with brine and dried (Na2S04) to give, after evaporation, 59.2 mg (99%) 647 [183] (Scheme 5.93). 

On bubbhng trimethylsilane 84 a into pyridine in the presence of catalytic amounts of Pd/C at different temperatures and for different reaction times four main products 1860-1863 and small amounts of three further products are obtained [83] (Scheme 12.23). 

This 580 to 280 K decrease in reaction temperature for trimethylsilane formation corresponds to a decrease in the reaction activation energy from 33 kcal/mol to -16 kcal/mol. Alternatively, if the rates of these processes could be measured at a common temperature, they would differ by more than 5 orders of magnitude. The fact that trimethylsilane is evolved at either 580 K or 280 K and not at temperatures in between suggests that there are distinctly different active sites for forming this product. The ratio of these active sites is a fimction of the temperature at which die surface is ion bombarded, and the transition from high to low temperature product evolution correlates directly with a factor of 1.5 to 2 increase in the Cu/Si... 

Figure 3. Temperature-programmed reaction spectra morutoring m/e = 73 (a cracking fragment of trimethylsilane) after adsorbing a saturation coverage of methyl groups on CusSi surfaces prepared by ion bombardment at 160 K (dotted curve) and 330 K (solid curve).

Several variations of the Peterson reaction have been developed for synthesis of alkenylsilanes.80 -P-Arylvinylsilanes can be obtained by dehydration of (3-silyloxy alkoxides formed by addition of lithiomethyl trimethylsilane to aromatic aldehydes. Specific Lewis acids have been found to be advantageous for the elimination step.81... 

Entries 6 to 8 demonstrate addition of allyl trimethylsilane to protected carbohydrate acetals. This reaction can be a valuable method for incorporating the chirality of carbohydrates into longer carbon chains. In cases involving cyclic acetals, reactions occur through oxonium ions and the stereochemistry is governed by steric and stereo-electronic effects of the ring. Note that Entry 8 involves the use of trimethylsilyl... 

Compared to the cyclic ketones, the coupling of aliphatic aldehydes to prepare 3-substituted indoles was less successful, except for phenyl acetaldehyde, which afforded 3-phenyl indole 83 in 76% yield (Scheme 4.22). The lack of imine formation or the instability of the aliphatic aldehyde towards the reaction conditions may be responsible for the inefficiency of these reactions. Therefore, a suitable aldehyde equivalent was considered. With the facile removal of a 2-trialkylsilyl group from an indole, an acyl silane was tested as a means of preparing 3-substituted indoles. Indeed, coupling of acetyl trimethylsilane with the iodoaniline 24 gave a 2 1 mixture of 2-TMS-indole 84 and indole (85) in a combined 64% yield. Evidently, the reaction conditions did lead to some desilylation. Regardless, the silyl group of 84 was quantitatively removed upon treatment with HC1 to afford indole (85). 

Regioselectivities that are usually high to excellent have been reported in novel palladium-catalyzed Heck arylation reactions with a variety of allylic substrates. The //-stabilizing effect of silicon enhanced regiocontrol in the internal arylation of allyl-trimethylsilane (Eq. 11.5) [18], and coordination between palladium and nitrogen... 

Equivalent amounts of aldehydes and alkoxytrimethylsilanes react to form unsymmetrical ethers in near quantitative yields in the presence of either trimethylsilane or triethylsilane and catalytic amounts (ca. 10 mol%) of TMSI in dichloromethane.329,333,334,341 The procedure is particularly convenient experimentally when trimethylsilane is used with TMSI because the catalyst provides its own color indicator for the reduction step (color change from deep violet to vivid red-gold) and the only silicon-containing product following aqueous workup is the volatile hexamethyldisiloxane (bp 99-100°). It is possible to introduce trimethylsilane (bp 7°) either as a previously prepared solution in dichloromethane or by bubbling it directly into the reaction mixture. Cyclohexyloxytrimethylsilane and n-butanal react by this method to give a 93% isolated yield of n-butyl cyclohexyl ether (Eq. 183).334... 

Trimethylsilane in pentane is a particularly good system for the TMSI-catalyzed reductive coupling of tertiary alkoxytrimethylsilanes with aldehydes to form sterically crowded tertiary-primary ethers.337 In this way, 1 -(tert-butoxymethyl)-3-methylbenzene is formed in 87% yield (Eq. 184).338 Reaction of terephthaldehyde with two equivalents of the trimethylsilyl ether of 1-adamantanol under these conditions leads to a good yield of the diadamantyl ether of 1,4-benzenedimethanol (Eq. 185).338... 

Hydrosilanes react with butadiene by the catalysis of palladium compounds, but the nature of the reaction is somewhat different from that of the telomerization of other nucleophiles described before. Different products are obtained depending on both the structure of silanes and the reaction conditions. Trimethylsilane and other trialkylsilanes reacted with butadiene to give the 1 2 adduct, l-trialkylsilyl-2,6-octadienes (65), in high yield (98%) (62-64). Unlike other telomers which have the 1,6-octadienyl chain, the telomers of silanes have the 2,6-octadienyl chain. As catalysts, Pd(PPh3)2 (maleic anhydride), PdCl2(PhCN)2, PdCl2, and 7r-allylpalladium chloride were used. Methyldiethoxysilane behaved similarly to give the 1 2 adduct. 

The hydrosilylation of butadiene proceeds with palladium compounds even in the absence of phosphines. Other ligands, such as glyoxime, benzonitrile, and 1,5-cyclooctadiene, can be used as effective ligands for the hydrosilylation of butadiene (65, 67). The reaction of trichlorosilane and dichlorosilane with isoprene proceeded regioselectively and stereo-selectively to give Z-l-trichlorosilyl-2-methyl-2-butene (67) (65, 66, 68). No reaction of trimethylsilane with isoprene took place, and this shows the lower reactivity of trialkylsilane. 

The reaction of trimethylsilane was found to be less selective at elevated temperatures. The following products were formed using PdCl2(PhCN)2 in benzene at 100°C (70) ... 

Analogous reactions were also used for the preparation of silyl derivatives, through reaction with (chloromethyl)trimethylsilane ... 

Nucleophilic Perfluoroalkylation of Nitrones The reaction of a,N-diaryl nitrones with (trifluoromethyl)trimethylsilane (TMSCF3) gives O-trimethylsilyl ethers of a-(trifluoromethyl)-hydroxylamines. This reaction is initiated by potassium ten -butoxide. Removal of the trimethylsilyl group on acid treatment leads to a-(trifluoromethyl)hydroxylamines, whereas catalytic hydrogenation gives a-(trifluoromethyl)amines (Scheme 2.194). 

Cycloaddition reactions of vinyl trimethylsilane with C -glycosyl nitrones gave moderate to good yields (67%-74%). Estimation of diastereoselectivities from isolated yields showed total endo preference for the reaction of the D-galacto nitrone. High endo preference was observed for the D-ribo analog, but exo preference for the D-xylo one (814). 

Several arylsubstituted dimeric iminoboranes have been prepared by the reaction of (phenylmethyleneamino)trimethylsilane with diorganohaloboranes or organodihaloboranes 47> according to Eq. (12). 

Tris(diphenylmethyleneamino)borane was obtained according to Eq. (30). Exchange reactions of monomeric and dimeric iminochloroboranes with various fluorides could not be effected. However, this lack of reaction is to be expected, since it is well known from borazine chemistry that substitutions which would require a structural change in order to obtain a stable product will not occur 20>. (Diphenylketimino)trimethylsilane (rather than diphenylketimine lithium) has been utilized successfully to prepare (diphenylmethyleneamino) dihaloboranes. This type of reaction is in accordance with earlier observa-... 

A highly air and moisture sensitive thiosilane PhS-SiCl3, which is prepared by the reaction of PhSLi with excess SiCl4, adds to terminal alkynes in the presence of Pt(CH2=CH2)(PPh3)2 at 110°C (Scheme 75).285 After treatment of the reaction mixture with MeLi, [(Z)-/ -(phenylthio)alkenyl]trimethylsilanes are obtained with high regio- and stereoselectivity. 

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