Carbonylative Et3SiH

Treatment of a pentacyclic la, I I -(2-oxethano) thioketal steroid with excess Et3SiH/TFA causes reduction of the carbon-carbon double bonds as well as the 17-carbonyl group to give a single reaction product (Eq. 213).368 Other work utilizes trifluoroacetic acid, triethylsilane, and anisole in the presence of a catalytic amount of boron trifluoride etherate to reduce the acetyl carbonyl of a 3-acetyl-2-azetidinone derivative with a dr of 8 1 (Eq. 214).395... 

The isomerization of a-alkylidene cyclic carbonyl compounds to a,/3-unsaturated cyclic carbonyl compounds was achieved by using catalytic amounts of RhCl(PPh3)3 and Et3SiH (Scheme 48).87... 

A single example of the reductive cyclization of allenic carbonyl compounds is reported, which employs a rhodium-based catalyst in conjunction with Et3SiH as terminal reductant.113 This protocol promotes hydrosilylation-cyclization to form both five- and six-membered rings with exceptional levels of yy -diastereocontrol. As revealed... 

In the first rhodium-catalyzed carbonylative silylcarbocyclization (CO-SiCaC), which was reported in 1992 [12, 13], silylcyclopentenone 9 was isolated as a minor product in the silylformylation of 1-hexyne 8 (Scheme 7.4). Under optimized conditions using Et3SiH and ( BuNC)4RhCo(CO)4 as the catalyst at 60°C, 9 is formed in 54% yield [13]. A possible mechanism proposed for this intermolecular CO-SiCaC is shown in Scheme 7.4 [13]. In this mechanism, the formation of 9 is proposed to proceed via in-... 

It was also possible to prepare a variety of deoxy analogs of 10 and 12 by reduction of the lactone carbonyl with DIBAH, and further reduction of the corresponding lactols with Et3SiH and BF3 OEt2 (Figure 9.7). The resultant deoxoartemisinin analogs 14, substituted at 3 and 9, have been reported.26... 

Sterically hindered alkenes can be hydrogenated at —50°C using triflic acid and a hydride donor.483 In addition to Et3SiH, transition-metal carbonyl hydrides such as HM(CO)3Cp (M = W, Mo, Os) and HMn(CO)5 (M = Mn, Re) are suitable hydride donors. Alkenes that form tertiary carbocation on protonation are hydrogenated in high yields (90-100%), whereas yields for styrenes are lower (50-60%). Alkynes are converted to the corresponding saturated hydrocarbon by using HW(CO)3Cp in combination with triflic acid.484... 

The ke[ values of photoinduced electron transfer reactions from [Ru(bpy)3]2 + to various nitrobenzene derivatives in the presence of 2.0 mol dm-3 HC104 are listed in Table 1, where the substituent effect is rather small irrespective of electron-withdrawing or donating substituents. A similar insensitivity to the substituent effect is also observed in the acid-catalyzed photoinduced electron transfer from [Ru(bpy)3]2+ to acetophenone derivatives [46,47]. The stronger the electron acceptor ability is, the weaker is the protonation ability, and vice versa. Thus, the reactivity of substrates in the acid-catalyzed electron transfer may be determined by two reverse effects, i.e., the proton and electron acceptor abilities, and they are largely canceled out. Such an insensitive substituent effect shows a sharp contrast with the substituent effect on the acid-catalyzed hydride transfer reactions from Et3SiH to carbonyl compounds, in which the reactivity of substrates is determined mainly by the protonation ability rather than the electron acceptor ability. 

Duckett and Perutz have shown the stoichiometric reaction of the CpRh(C2H4)(SiR3)H (R = Et, i-Pr) complexes (Scheme 33)201. These complexes have been found to act as precursors to the catalytically active species for the hydrosilylation of ethene with Et3SiH but are not within the catalytic cycle. The mechanism proposed in Scheme 34 for the hydrosilylation of ethene was found to be equivalent to the Seitz-Wrighton hydrosilylation mechanism catalyzed by cobalt carbonyls complexes202. 

The Cio lactone carbonyl oxygen was removed by diisobutylaluminium hydride (DIBAL) reduction, followed directly by a second reduction (BF3-OEt2/Et3SiH) to convert ring C into a pyran ring (Scheme 5). <2002JME4321>. 

In 1993, Murai s group examined the effectiveness of the iron-triad carbonyl complexes Fe(CO)5, Fe2(CO)9 and Fe3(CO)12 as catalysts for the reaction of styrene with triethylsilane [47]. Whereas Fe(CO)5 showed no catalytic activity, Fe2(CO)9 and Fe3(CO)12 formed selectively P-silylstyrene 57a and ethylbenzene 58. Interestingly, Fe3(CO)12 is the catalyst that exhibited the highest selectivity. This trinuclear iron carbonyl catalyst was also successfully applied in the reaction of different para-substituted styrenes with Et3SiH giving only the (E)-P-triethylstyrenes in 66-70% yield (Scheme 4.23). 

Facile reduction of C02 was found by rhodium compounds. Svoboda and Mctflcjs studied the reaction of chlorotris(triphenylphosphine)rhodium and CO2 in the presence of the organosilicon hydrides Et3SiH or HSi(OEt)3 (287,288). They observed the formation of the rhodium-carbonyl complex RhCI(CO) (PPh ), althougli attempts at isolating the analogous RuCl(CO)(PPh,>2 were... 

Alkylsilanes have been shown to be versatile deprotection reagents for the benzyloxycarbonyl group. This is achieved by treatment with Et3SiH/PdCl2,f or by reaction with tert-butyldimethylsilane/Pd(OAc)2 which allows the corresponding tert-butyldimethylsiloxy-carbonyl-protected amino acids to be isolated.t l... 

An ESR study of the photolysis of a Re2(C0),o-Et3SiH system has been described and the rate constcuit for abstraction of H from EtjSiH by Re(CO)s measured. Photosubstitution of a carbonyl group in Re2(C0),o with P(OPh)3 gives four well-characterised products. The observed pattern of disubstituted cmd triply... 

Ether synthesis. Carbonyl compounds undergo reductive etherihcation with ROH in a reaction with Et3SiH, which is catalyzed by FeCl3. 

The hydrosilylation of carbonyl confounds with Et3SiH (eq 4) has also been the subject of additional research. Owing to these efforts, carbonyls can now be directly converted to their tri-ethylsilyl (TES) ethers with copper catalysts in the company of a bidentate phosphine or Al-heterocycUc carbene ligand. Tri-ethylsilyl ethers can also be made from carbonyl compounds and EtsSiH in the presence of rhenium(V) oxo-complexes. ... 

When reacting alkenes with triethylsilane it is necessary to keep in mind that the PdCl2/Et3SiH combination also promotes the double bond isomerization of monosubstituted aliphatic olefins and a-alkylidene cyclic carbonyl compounds are isomerized to a,/3-unsaturated cyclic carbonyls with tris(triphenylphosphine) rhodium chloride. ... 

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