Silanes synthesis from

In addition to transition metals, recent work has demonstrated that strong Lewis acids will catalyze the addition of silanes to alkynes in both an intra- and an intermolecular fashion.14,14a-14c The formation of vinylsilanes from alkynes is possible by other means as well, such as the synthetically important and useful silylcupration15,15a of alkynes followed by cuprate protonation to afford vinylsilanes. These reactions provide products which can be complementary in nature to direct hydrometallation. Alternatively, modern metathesis catalysts have made possible direct vinylsilane synthesis from terminal olefins.16,16a... 

Reagents A Convenient Route to sec- and tert- 6-Alkylpurines. Tetrahedron Lett. 1996, 37, 1285-1288. (c) Dvorakova, H. Dvorak, D. Holy, A. Synthesis of Acyclic Nucleotide Analogues Derived from 6-(sec- or tert-Alkyl) purines via Coupling of 6-Chloropurine Derivatives with Organocuprates. Collect. Czech. Chem. Commun. 1998, 63, 2065-2074. (d) Hocek, M. Holy, A. Perfluoroalkylation of 6-Iodopurines by Trimethyl(perfluoro-alkyl)silanes. Synthesis of 6-(Perfluoroalkyl)purine Bases, Nucleosides and Acyclic Nucleotide Analogues. Collect. Czech. Chem. Commun. 1999, 64, 229-241. 

Kumada et al.359 prepared linear methylpolysilanes up to n = 12 by Wurtz synthesis from different chloromethyldisilanes and found by investigation of the physical constants that the melting points of the silanes up to n = 7 do not rise continuously but follow in a zigzag course since the polysilanes with an odd number of silicon atoms melt at a lower temperature, than those with an even number of silicon atoms, though this effect is less pronounced with higher n. 

Table 4.2-1. Average Composition of a Raw Silane Mixture from Industrial Direct Synthesis.

Relatively non-toxic tris(trimethylsilyl)silane performs the same function as Bu3SnH in standard radical-chain reactions, such as hydrocarbon synthesis from ethylene derivs. and iodides. E A mixture of cyclohexyl iodide, acrylonitrile, and 1.2 eqs. tris(trimethylsilyl)silane in toluene heated at 70-90° for 4-5 h in the presence of a little AIBN product. Y 90%. Regioselectivity may also be enhanced, and reaction times... 

A method for the preparation of halosilyl carbamates and isocyanate involves direct synthesis from amines via halosilyl carbamate intermediates [277]. A primary amine is converted to its carbamic acid salt, which is then treated with a silane containing > 2 halogen atoms bonded to Si. Gentle heating of the resulting halosilyl carbamate gives the isocyanate. In an alternative (exchange) procedure, the carbamic acid salt is treated with any halosilane to form a silyl carbamate, which is trans-silylated. 

Kondo et al. reported on the synthesis of acyl(methyldiphenyl)-silanes starting from dichlorobis(methyldiphenylsilyl)methane... 

Studies on the stereochemical outcome of the reaction of 2-alkenyl organometallic reagents with aldehydes have increased recently, largely because stereoselectively produced homoallylic alcohols are synthetically equivalent, by cleavage at the carbon-carbon double bond, to the type of aldol adduct stereoisomers required for macrolide antibiotic total synthesis. A new stereoselective synthesis of (Z)-2-alkenyltins (46a) or the corresponding silanes (46b) from allyl or vinyl 9-BBN derivatives has appeared (Scheme 20). The... 

Substituted allenes are obtained from the reaction of propargyl silanes (prepared from lithium alkynes and trimethylsilylmethyl chloride ) and electrophiles. An exocyclic allene is produced when this reaction involves ring closure, a method which has been applied in a biomimetic steroid synthesis (Scheme 16). ° If the corresponding trimethylsilylalkyne is used a D-homosteroid system is obtained. ... 

Scheme 7 Combinatorial approach for the synthesis and screening of CIL-modified silanes. Adapted from [102]...

Vinyl silanes continue to attract attention as intermediates for the stereoselective synthesis of olefins. Zweifel and Lewis now describe the stereoselective synthesis of both -and Z-(l-halogenoalk-l-enyl)silanes (15) from alk-l-ynyl-silanes, and show how they may then be processed to dialkyl-substituted vinyl-silanes, alkenyl halides, and trisubstituted olefins (Scheme 12). The E-l-halogenoalkenyltrimethylsilanes are readily prepared in high isomeric purity by treatment of the dialkylhydroalumination adduct (14) with N-chlorosuccinimide,... 

Non-metallic homogeneous catalyst systems were also reported for methanol synthesis. Recently, Ashley et al. [49] demonstrated the selective hydrogenation of COj to methanol using a FLP-based nomnetal mediated procedure at low pressures (1-2 atm). N-Heterocyclic carbine (NHC) was found to be an elFective organic catalyst for methanol synthesis from CO2 reduction with silane. Compared to transition metal catalyst, NHC is more efficient at ambient reaction conditions [50,51]. Table 5.1 lists catalytic activities of different heterogeneous catalysts employed for methanol synthesis from CO. It shows that maximum CO conversion of 25.9%, methanol selectivity of 99.5% and methanol yield of378 mg/g-cat h could be achieved. The space velocities were tried between 1800 and 18,000 h and the temperature from 170 to 270 C. 

Vinyl silane 174 (from L-arabinose) undergoes a series of stereoselective cyclization reactions, the outcomes of which are determined by the nature of the Lewis acid used (Scheme yj) The N-tosylimine adduct 175 has been converted to the protected lycoriddine derivative 176 Full details of Ogawa s synthesis of (+)-lycoricidine have appeared (Vol. 25, p.320). 

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