Triethylsilane, as reducing agent

Improved selectivities to the alcohol have been found with bis(trifluoroacetylacetonato)cobalt(II) as catalyst [240] and triethylsilane as reducing agent [241]. This method is also suitable for the synthesis of triethylsilyl peroxides from olefins [242]. 

Mukaiyama and Kobayashi et al had reported the first use of In(III) salts in the reduction of 0-trimethylsilyl monothioacetals to the corresponding sulfides using triethylsilane as reducing agent. Such a reaction was found to be best catalyzed by the InCl3-TMSCl ion pair, with TiCU, BF3 Et20, and SnCU having no activity... 

Other reduction methods are also used. Diethyldifluorosilane was reduced to diethylsilane [133] (98 %) with metallic sodium and hydrogen (in an octane solution, pressure 150 atm. at 290 °C, 2.5 h). Chloroorganosilanes can be reduced with sodium hydride in an HMPT solution. Even at 23 C, the yield is good [134] triethylsilane, 100% diethylsilane, 70%, butylsilane, 82%. Calcium hydride in the presence of AICI3 [135] alkylaluminium hydride [136] and the system Mg/trimethylamine/hydrochloric acid [137] (Eq. 3.40) are equally effective as reducing agents. 

The reduction is general for a variety of substituted benzophenones Such substituents as CH3 OH, OCH3, F, Br. N(CH3)2, NO2. COOH, COOCH3, NHCOC Hreaction conditions and do not alter the course of the reduction Diarylmethanols are reduced to diarylmethanes under the same conditions and probably are the intermediates in the reduction of ketones [26] Triethylsilane also can be used as a reducing agent in trifluoroacetic acid medium [27J This reagent is used for the reduction of benzoic acid and some other carboxylic acids under mild condiUons (equation 14) Some acids (phthalic, sue cinic, and 4-nitrobenzoic) are not reduced under these conditions [27]... 

Reductive Amidation of Aldehydes. The reductive amidation of aldehydes using an organosilane as the reducing agent has been realized. Benzaldehyde reacts over a 74-hour period with triethylsilane and acetonitrile in 75% aqueous sulfuric acid at room temperature to produce an 80% isolated yield of N-benzylacetamide (Eq. 169).313 Octanal fails to react under the same conditions.313 Reductive amidation of aldehydes also occurs with the reagent combination Et3SiH/TFA/primary amide (Eq. 170).326... 

The use of trimethylsilyl-based electrophilic catalysts with organosilicon hydrides also promotes the conversion of aldehydes into ethers and avoids the need to employ the potentially hazardous trityl perchlorate salt.314,334,338 One reagent pair that is particularly effective in the reductive conversion of aldehydes into symmetrical ethers is a catalytic amount of trimethylsilyl triflate combined with either trimethylsilane, triethylsilane, PMHS,334 or 1,1,3,3-tetramethyldisiloxane (TMDO, 64) as the reducing agent (Eq. 179).314 Either... 

Reduction of the ketone carbonyl of cis-1, 2,3,4,4a,9b-hexahydro-8-hydroxydi-benzofuran-3-one with trifluoroacetic acid and triethylsilane at 0° produces a mixture of the a- and /3-isomers of the C3 alcohol with an u / ratio of 1 4 (Eq. 211).394 This result can be compared with the isomer ratio of 100 1 that results when sodium borohydride is used as the reducing agent.394 The same cis pair of alcohol isomers is formed in 77% combined yield, but in a reversed ratio of a /3 = 4 1, when the less saturated tetrahydrodibenzofuran analog is used as the substrate (Eq. 212).394... 

A related (tandem) SNlreduction will be introduced in Figure 17.72. There a benzyl(tri-ethylsilyl) ether undergoes reduction by triethylsilane as a reducing agent and trifluoroacetic acid as a Bronsted acid. 

An acid promoted hydrolysis is usually slower than a similar base promoted hydrolysis. In some cases, as with a z-butyl ester, however, acid catalyzed hydrolyses are preferred. With the Z-butyl ester, sometimes a reducing agent such as formic acid or triethylsilane is added to scavenge the carbocation. 

Stereoselective reduction of bicyclic ketals. A new route to 6- and 8-membercd cyclic ethers involves stereoselective reduction of the bicyclic ketals such as 2. Depending on the reducing agent, the bicyclic ketal 2 can be reduced to either the cis- or trans-cyclic ether 3. Thus reduction of 2 and 4 with triethylsilane and TiCl4 at -78° yields the ci.s-disubstituted cyclic ethers 3 and 5 with high stereoselectivity. Reduction of 2 and 4... 

As with the similarly polarized boron and aluminium hydrides, hydrido-silanes can transfer formal hydride ions to electropositive carbon centres. Unlike the first two reducing agents, hydridosilanes require additional activation of the carbon centre by Lewis or protic acids before such hydride transfer can take place. This overall process is known as ionic hydrogenation (4). The reagent system of triethylsilane and boron trifluoride etherate has provided an extremely selective method for the reductive deoxygenation of lactols (5), derived in turn from DIBAL reduction (6) of the corresponding y- or 6-lactones ... 

Introduction. Triethylsilane serves as an exemplar for organosilicon hydride behavior as a mild reducing agent. It is frequently chosen as a synthetic reagent because of its availability, convenient physical properties, and economy relative to other organosilicon hydrides which might otherwise be suitable for effecting specific chemical transformations. 

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