Alkynes triethylsilane

The use of stronger acid conditions provides somewhat better synthetic yields of alkanes from alkynes. A useful method consists of treatment of the substrate with a combination of triethylsilane, aluminum chloride, and excess hydrogen chloride in dichloromethane.146 Thus, treatment of phenylacetylene with 5 equivalents of triethylsilane and 0.2 equivalents of aluminum chloride in this way at room temperature yields 50% of ethylbenzene after 1.5 hours. Diphenylacetylene gives a 50% yield of bibenzyl when treated with 97 equivalents of triethylsilane and 2.7 equivalents of aluminum chloride after 2.8 hours. Even 1-hexyne gives a mixture of 44% n -hexane and 7% methylpentane of undisclosed structure when treated with 10 equivalents of triethylsilane and 0.5 equivalent of aluminum chloride for 0.5 hour.146... 

Ruthenium complexes do not have an extensive history as alkyne hydrosilylation catalysts. Oro noted that a ruthenium(n) hydride (Scheme 11, A) will perform stepwise alkyne insertion, and that the resulting vinylruthenium will undergo transmetallation upon treatment with triethylsilane to regenerate the ruthenium(n) hydride and produce the (E)-f3-vinylsilane in a stoichiometric reaction. However, when the same complex is used to catalyze the hydrosilylation reaction, exclusive formation of the (Z)-/3-vinylsilane is observed.55 In the catalytic case, the active ruthenium species is likely not the hydride A but the Ru-Si species B. This leads to a monohydride silylmetallation mechanism (see Scheme 1). More recently, small changes in catalyst structure have been shown to provide remarkable changes in stereoselectivity (Scheme ll).56... 

Another reaction is reductive cyclization. 1,6-Diynes and 1.6-enynes undergo reductive cyclization using hydrosilanes as a hydrogen source in AcOH. The 1,6-diynes 91 and 95 are converted into the 1,2-dialkylidenecyclopentane derivatives (1,3-dienes) 94 and 96. Triethylsilane is used as a hydrogen donor for the reaction[48]. The reaction involves the formation of a vinylpalladium bond in 92 via the insertion of an alkyne into the Pd—H bond, followed by the alkyne insertion to give 93, which is hydrogenolyzed with Si—H to give the 1,3-dienes 94 and 96. 

Another reaction is reductive cyclization of 1,6-diynes and 1,6-enynes using hydrosilanes as a hydrogen source in AcOH. Triethylsilane is used as the hydrogen donor for this reaction [142], The reaction can be understood by the formation of vinylpalladium bond 350 via the insertion of alkyne 349 to the Pd—H bond in 328. Then intramolecular alkyne insertion gives vinylpalladium 351, which is hydro-genolysed with Si—H to give the 1,3-diene 352 by transmetallation and reductive... 

The cationic ruthenium complex [CpRu(MeCN)3]+(PF6) catalyses the hydro-silylation of alkyne with triethylsilane in good yield and with very limited formation of Unear 1,2-disubstituted products (Eq. 17, Table 4). 

Recent evidence for the formation of hemiketal intermediates iqmn acylation of alkynides has been obtained from glucopyranolactones. Treatment of tetrabenzyl (55) with the anion from l-benzyloxy-3-bu-tyne gave a quantitative yield of hemiketal (56) which showed IR absorptions for the OH and alkyne portions of the molecule (X = 3350 cm" and 2250 cnr, respectively). This compound was stereospecifi-cally reduced to the C-glycoside (57) with triethylsilane/BFs-etherate (overall yield 72% Scheme 18). None of the other stereoisomer or ring-opened product was obtained. ... 

Among the many available procedures for preparing alkenylsilanes are hydrosilylation of alkynes and partial reduction of alkynylsilanes. Hydrosilylation of 1-alkynes with triethylsilane in the presence of catalytic chloroplatinic acid results in regioselective... 

Reductive decomplexation/ Although the common practice for removal of the hexacarbonyldicobalt residue from alkyne complexes involves mild oxidants, it is also possible to convert the complexes to free (Z)-alkenes with BUjSnH. If triethylsilane is used the decomplexation is followed by in situ hydrosilylation. 

The intermediacy of the complex [Os(SiEt3)Cl(H2)(CO)(P Pr3)2] in the catalytic hydrosilylation of phenylacetylene was first observed by Oro and co-workers when the neutral hydride [OsHCl(CO)(P Pr3)2] was reacted with triethylsilane and the alkyne [81]. A theoretical study of silane addition across the C-C triple bond has also been reported [82] and the general scope of this reaction has been amply reviewed [17],... 

Triphenylsilyl ethers are typically prepared by the reaction of the alcohol with triphenylsilyl chloride (mp 92-94 °C) and imidazole in DMF at room temperature. The dehydrogenative silylation of alcohols can be accomplished with as little as 2 mol% of the commercial Lewis acid tris(pentaf1uorophenyl)borane and a silane such as triphenylsilane or triethylsilane [Scheme 4.98]. Primary, secondary, tertiary and phenolic hydroxyls participate whereas alkenes, alkynes, alkyl halides, nitro compounds, methyl and benzyl ethers, esters and lactones are inert under the conditions. The stability of ether functions depends on the substrate. Thus, tetrahydrofurans appear to be inert whereas epoxides undergo ring cleavage. 1,2- and 1,3-Diols can also be converted to their silylene counterparts as illustrated by the conversion 983 98.4. Hindered silanes such as tri-... 

Hydrosilylations. Addition of triethylsilane across multiple bonds occurs under the influence of a large number of metal catalysts. Terminal alkynes undergo hydrosilylations easily with triethylsilane in the presence of platinum, rhodium, ruthenium, osmium, or iridium catalysts. For example, phenylacety-lene can form three possible isomeric hydrosilylation products with triethylsilane the (Z)-/3-, the and the a-products... 

Additional Hydrosilylations. Hydrosilylations of terminal alkynes with triethylsilane (eq 1) have been improved in terms of their regio- and stereocontrol as well as in other aspects of their operation. Through the employment of Pt(DVDS), Pt-catalyzed hydrosilylations of 1-alkynes can now be performed at room temperature and in water with very high selectivity for the ( )-/3-vinylsilanes (eq 20). It has also been shown that Pt02 catalyzes the internal hydrosilylation of aryl alkynes under orthosubstituent regiocontrol (eq Strong preference for the... 

Lewis acids have also been demonstrated to catalyze terminal and internal alkyne hydrosilylation. Aluminum chloride and EtAlCl2 were found to be very active catalysts for the hydrosilylation with triethylsilane producing the corresponding (Z)-vinylsilane with high regio- and stereoselectivieties as a result of trans addition (4). 

To further substantiate the validity of this correlation, we decided to probe the influence of the cr-donating ability of the NHC on the regioselectivity. For this purpose, the hydrosilylation of phenylacetylene by triethylsilane imder the standard conditions was performed with three catalysts possessing the same limited steric hindrance but completely different electronic properties (Figure 5.18) [32]. As can be seen, identical selectivities were obtained, despite the fundamental differences between the catalysts, thereby reinforcing our proposal that the regioselectivity of the hydrosilylation of alkynes is controlled essentially by steric parameters. It is noteworthy that the major isomer obtained in this case is the a-adduct. This is not surprising since arylacetylenes are known to lead... 

SCHEME 5.63 Ni(COD)-IMes-catalyzed reductive coupling of alkynes, aldehydes, and triethylsilanes. 

The disc-shaped plastic micoreactors, termed microcapillary films (MCFs), contain 19 parallel microchannels, each with a mean internal diameter of 142 10 pm. The material was prepared using a melt extrusion process from an ethylene-vinyl alcohol copolymer (EVOH) [28]. Immobilization of palladium(0) on the wall surface inside the MCFs was performed by simple chemical deposition techniques (Scheme 7.3). The palladium-coated capillaries were used for transfer hydrt enation of ketones, imines, nitro compounds, alkenes, and alkynes with triethylsilane under flow conditions [29]. Microcapillaries whose inside surfaces were coated with copper or gold were also utilized for the continuous-flow reactions [30]. 

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