Silane To alcohol

KUMADA-FLEMING Swreoselective hydroxylalion Stereoselective conversion of aAcyl silanes to alcohols... 

Stereoselective conversion of alkyl silanes to alcohols by means of peracids. 

AUylamines. Xmines are ally I an Mo-catalyzed reaction with f-BuOO Silanes to alcohols. Hindered... 

Silanes to alcohols. Hindered silanes are cleaved by treatment with t-BuOOH-KH... 

The length of the axial bond would be expected on all theories to be important. The barrier height does decline from ethane to methyl silane to methyl germane, but of course the bonded atoms are different. Unfortunately reliable values are not available for dimethyl mercury, dimethyl acetylene, and similar molecules with still longer bonds. An apparent exception is provided by methyl mercaptan and methyl alcohol. The latter, with the shorter axial bond, has the lower barrier. 

Allyl silanes react with epoxides, in the presence of Bp3-OEt2 to give 2-allyl alcohols. The reaction of a-bromo lactones and CH2=CHCH2Si SiMe3)3 and AIBN leads to the a-allyl lactone. " Benzyl silanes coupled with allyl silanes to give ArCH2—R derivatives in the presence of VO(OEt)Cl2 " and allyltin compounds couple with allyl silanes in the presence of SnCU. " Allyl silanes couple to the a-carbon of amines under photolysis conditions. ... 

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-... 

Reaction of lithiated allylbenzotriazole 452 with chloromethyltrimethylsilane yields silyl derivative 464 which can be further alkylated to give compound 465 (Scheme 76) <1999JOC1888>. Upon heating, product 465 is readily converted to diene 466 via vicinal elimination of benzotriazolyl and silyl substituents. Additions of lithiated silyl derivative 464 to carbonyl groups of aldehydes lead to alcohols 463 which readily eliminate benzotriazole and silane to furnish 2-(l-hydroxyalkyl)butadienes 466 (R1 = 1-hydroxyalkyl). 

Carbamate and amide groups have been found to be stable under these coupling conditions73. In the presence of TiCLt or SnCLt, chiral a-keto amides 36 react with allyl-silane to produce, after hydrolysis, optically active tertiary alcohols 37 with extremely high optical selectivity (equation 23)74. The addition reaction appears to occur from the Si face of the carbonyl group. In a similar manner, a high degree of stereoselectivity is obtained from the reactions of A-Boc-a-amino aldehydes 38 with 2-substituted allylsilanes (equation 24)75. 

This compound can disproportionate, generating silane (SiPLt) which is liable to be pyrophoric. Presumably other alkoxy silanes can do likewise [ 1], Its use as a reducing agent for the preparation of alcohols from esters is considered safer in air than under an inert atmosphere, which latter permits accumulation of silane to hazardous levels and later fire or explosion. [2]... 

Upon treatment with TiCl3(OCHMe2), compound 32 reacts with allyltrimethyl-silane to form ether 33 in good yield and selectivity. The chiral template is then removed by treatment with an excess of LDA affording the desired homoallylic alcohol 34 in 80-94% ee. 

During our investigation of the reactivity of the 10 % Pd/C catalyst, we found that le reacts with itself forming dimeric compounds (Scheme 32). This problem was solved by slow addition of the silane to a mixture of the alcohol and catalyst in the second alcoholysis step. We proposed that the silyl ether is activated by the catalyst and intramolecular dimerization occurs on the surface of the catalyst (Figure 8). This reaction is faster than the usual intermolecular reaction of the incoming alcohol with the silane, resulting in the dimeric products. 

Oxidative addition of the silane to the metal is fast and reversible 30 therefore unless the pentacoordinated silane drastically slows down the oxidative addition process, pentacoordination will not alter the rate of the reaction at this stage of the cycle. The increased reactivity of le may be explained by the attack of the alcohol on the pentacoordinated silane that would form after oxidative addition (Figure 9A). The rate of the alcohol addition is increased by the higher reactivity of the pentacoordinated silicon center. This may explain the slower reactivity for those alkoxysilanes that cannot form this intramolecular coordination complex due to the absence of a nearby Lewis basic atom. We had observed during the comparison of aliphatic alcohol to benzyl alcohol that the nucleophilicity of the alcohols has an effect on the rate of the reaction. This is evidence that the alcohol and the silane are involved in the rate-determining step with 10 % Pd/C catalytic system. 

We proposed a mechanistic outline (Figure 10) and carried out several reactions in order to get an insight into the mechanism. We have demonstrated that the silane and alcohol are involved in the rate-determining step for the 10 % Pd/C catalytic system. It was documented with Brookhart s iron catalyst that the rate determining step for that system was the dissociation of molecular hydrogen from the metal assisted by the silane.15 If the rate determining step is the same for our manganese catalyst as Brookhart s catalyst, then the concentration and lifetime of... 

The accelerated rate for alcoholysis with le, which was observed for the 10 % Pd/C catalytic system, was also seen with the Mn(CO)sBr catalyst. Reactions of le with primary, secondary or tertiary alcohols resulted in moderate yields of the corresponding silyl ketals after 2 h (Table 8 and 9). When mono-alkoxy silane from 3-hydroxy butyrate (lg) was treated with homoallyl alcohol in the presence of Mn(CO)sBr as the catalyst under the standard conditions, 76 % of the silyl ketal was obtained. These silyl ethers possess neighboring carbonyl groups that can participate in the reaction by forming a more reactive pentacoordinated silicon center upon addition of the silane to the metal center.. 

Dehydrodimerization. On excitation with a mercury vapor lamp, mercury is converted to an excited state, Hg, which can convert a C—H bond into a carbon radical and a hydrogen atom. This process can result in dehydrodimerization, which has been known for some time, but which has not been synthetically useful because of low yields when carried out in solution. Brown and Crabtree1 have shown that this reaction can be synthetically useful when carried out in the vapor phase, in which the reaction is much faster than in a liquid phase, and in which very high selectivities are attainable. Secondary C—H bonds are cleaved more readily than primary ones, and tertiary C—H bonds are cleaved the most readily. Isobutane is dimerized exclusively to 2,2,3,3-tetramethylbutane. This dehydrodimerization is also applicable to alcohols, ethers, and silanes. Cross-dehydrodimerization is also possible, and is a useful synthetic reaction. 

The Lewis acid BF3) opens the epoxide to give the tertiary cation, which cyclizes on to the ally silane to give a 3-silyl cation that loses the Me3Si group in the usual way. It is clear from the product what the stereochemistry of this intermediate must be and it looks as though cyclization gives the more stable di-equatorial product (margin). Probably the cation folds up in this conformation. The alcohol controls the new centre and is then removed by oxidation to a ketone. 

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