Silanes from halides

Catalytic reduction of RX.2 This silane can be used in catalytic amounts in the radical reduction of alkyl halides if NaBH4 is added to regenerate the silane from the [(CH3)3Si]3SiX formed on reduction of RX by 1. Yields in the catalytic hydrodehalo-genation process are only slightly lower than those obtained by use of an equimolar amount of the silane. 

Syntheses of unsymmetrical allyl silanes from Grignard reagents are subject to the usual regioselectivity problems. The mixture of halides 81 and 82 gives a mixture of Grignard reagents,... 

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,... 

Vinyl Acetate CH3COOCH=CH2 OH compds, HCN, Halides, Halogens, Mer-cap tans, Amine, Silanes Oxygen Vap in Air 2.6 to 13.4% > Ambient > Ambient Inhibitor—Methyl Ether of Hydroquinone or 3-5ppm Diphenylamine. Store in a dry, cool place shield from light impurities 20.9-21.5 402 427 Free-radical polymerization initiated by Benzoyl Peroxide... 

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

Interesting cyclic ionic species are obtained from the reactions of di(phosphazenyl)silanes with silicon halides at room temperature ... 

Efforts to tune the reactivity of rhodium catalysts by altering structure, solvent, and other factors have been pursued.49,493 50 Although there is (justifiably) much attention given to catalysts which provide /raor-addition processes, it is probably underappreciated that appropriate rhodium complexes, especially cationic phosphine complexes, can be very good and reliable catalysts for the formation of ( )-/3-silane products from a air-addition process. The possibilities and range of substrate tolerance are demonstrated by the two examples in Scheme 9. A very bulky tertiary propargylic alcohol as well as a simple linear alkyne provide excellent access to the CE)-/3-vinylsilane products.4 a 1 In order to achieve clean air-addition, cationic complexes have provided consistent results, since vinylmetal isomerization becomes less competitive for a cationic intermediate. Thus, halide-free systems with... 

Allenyllithium reagents are commonly prepared through lithiation of propargylic halides or by deprotonation of alkynes or certain allenes (Eq. 9.1). Lithiated allenes often serve as precursors to stable allenylmetal compounds such as stannanes or silanes. They can also be employed for the in situ synthesis of allenylzinc, -titanium and -boronate compounds, which can be further transformed to substitution products not accessible from their allenyllithio precursors. 

Fig, 9.34, Apparatus used for the preparation and sampling of Grignard reagents for NMR spectroscopy. The apparatus was evacuated through J2 and the Mg baked. Excess ether and alkyl halide were distilled onto the metal, and the apparatus was sealed off at S3. Upon warming to 0°C and shaking, a rapid reaction occurred. The apparatus was evacuated at Jj, the break-seal B was broken, and ether and excess alkyl halide were removed. Fresh dry ether and the letramethyl silane standard were distilled in, the apparatus was sealed off at S, and a small portion of the solution was filtered through the frit F into the NMR tube, which was sealed off at S2. (Adapted from D. F. Evans and J. P. Mahler, / Chem. Soc.t 1962, 5125.)... 

Several authors have demonstrated the feasibility of the alkylation of a MSMA substrate to obtain the homologous RSMA via reaction of the corresponding a-silylcarbanion with an alkyl halide. Treatment with LDA of (allyl)(pyrrazolylmethyl) silane gives a carbanion that on trapping with methyl iodide, leads to the unique formation of the corresponding RSMA derivative without traces of compounds that could have resulted from the allylic system. However, when. v-butyllithium is used instead of LDA, partial methylation of this system also occurs.66... 

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