Silyllithium preparation

Hydrido(trialkylsilyl)silyllithiums, preparation, 3, 424 Hydroacylations, olefins, 10, 142 Hydroalkoxylations and etherification, 10, 672 in etherification, 10, 683 Hydroaluminations for C-E bond formation characteristics, 10, 857 chemoselectivity, 10, 859 mechanism, 10, 858 overview, 10, 839-870 stereoselectivity, 10, 861 total synthesis applications, 10, 865 characteristics, 3, 275 process and examples, 9, 268 via Ti(IV) complexes, 4, 658 Hydroaminations actinide-catalyzed, 4, 237 in aminations... 

Kawakami et al. have prepared optically active bifunctional l,3-dimethyl-l,3-diphenyldisiloxanes.158,159 Strohmann et al. have prepared enantiomerically enriched Si-centered silyllithium compounds, which react stereo-specifically with triorganochlorosilanes.160-162 In solution, slow racemization of the silyllithium compounds takes place, which, however, can be circumvented by transmetallation with MgBr2. Oestreich et al. prepared new Si-centered cyclic silanes adopting the strategies developed by Corriu and Sommer.163 Bienz et al. have developed enantioselective routes for the preparation of C-centered chiral allenylsilanes.156,164-166... 

More recently, Kira et al. have published a new route to the preparation of hydrido(trialkylsilyl)silyllithiums, such as (/-BuMe2Si)2SiHLi 160,298 which show promise as versatile starting materials in organometallic synthesis. 

Amino-substituted silyllithium compounds have been prepared by Tamao and coworkers from the corresponding chlorosilanes by treatment with either a dispersion of lithium metal... 

V,/V-Dialkyl-RSMAs have been prepared by addition of silyllithium reagents to iminium salts formed in situ by reacting aldehydes with silylamines in the presence of lithium perchlorate. Although excellent yields have been obtained, except when starting from enolizable aldehydes, the use of the dangerous reagent lithium perchlorate makes this procedure less attractive.197... 

Preparation of the branched silane began with the reaction of tris(trimethylsilyl)silane with CHC13 (CC14) and MeLi to afford the peralkylated methyl[tris(trimethylsilyl)]-silane. Subsequent treatment with A1C13 and ClSiMe3 gave the trichlorosilane, which was then reacted with tris(trimethylsilyl)silyllithium yielding the final silane dendrimer. 

Following this scheme, Me3GeLi was prepared from Me3GeCl and lithium in HMPA/ Et20 (equation 18)32 and then used in the preparation of germasilanes, which are useful in the synthesis of stable silyllithiums (equation 19)32. 

There is also a series of anions of the type ERj. The best studied are the silyl anionsespecially the silyllithiums. For example, Si(SiMe3)3 is a versatile reagent for the synthesis of a great variety of polysilyl derivatives. It can be prepared by the reaction of Si(SiMe3)4 and methyllithium97 according to... 

Silyllithium compounds may also be prepared by the transmetalation reaction between silylmercury and Li. The requisite silylmercury may be prepared from the corresponding chlorosilane or hydrosilane. The latter can be applied to the synthesis of polysilanyllithium. Equation (17) is an example. ... 

Diethylamino-substituted silyllithium is prepared successfully and used for the preparation of silicon-functional compounds (equation 18). ... 

Silyllithiums are the most popular and most extensively investigated species among the silyl anions, and can be prepared by the following methods ... 

Reactions of silylcuprates provide additional examples of a silyl anion based mechanism (Scheme 3). The reagent (19), prepared from silyllithium and copper(I) cyanide, reacts with a C=C bond to give, after aqueous work-up, c/j-hydrosilylated products (20). Conjugate addition of (21) to a,P-unsaturated... 

The reaction of the enantiomerically enriched silyllithium compound 4 [prepared from disilane (/J)-12] with cyclopropylmethyl chloride occurs with retention of the configuration [(/ )-14], while, for cyclopropylmethyl bromide and iodide, mainly Inversion of the configuration [(S)-14] was observed. The products of the radical reaction (15) indicate a racemization at the silicon center. 

Solutions of the silyllithiums PhjSiLi, MePh2SiLi and Mc2PhSiLi suitable for kinetic studies may be prepared under vacuum . 

Preparation and Structure of Tris(tetrahydrofuran)tris(trimethylsilyl)silyllithium... 

Since the preparation of anionic species or organosilicon compounds is largely restricted by its reaction conditions, the synthetic utility of silyl anions for the synthesis of organosilicon compounds is limited. However silyllithiums possessing one or more phenyl groups on a silicon atom are readily prepared by the reductive metallation of the corresponding halosilanes with lithium. Allylsilanes are synthesized by the reaction of allyl acetates with the cuprate prepared from such a reagent (eq (47)) [43]. 

Halogen-free solutions may be obtained by cleavage of a disilane with elemental lithium or methyllithium, or by reaction of disilylmercury compounds with lithium. Other methods of preparation have been reviewed1, and this same source discusses the Grignard-like reactions of silyllithium and other silylmetal reagents. 

Elimination of silanes from a-silyl alcohols. By this oxidation acylsilanes can be prepared in two steps from esters and amides reaction with silyllithiums and PCC oxidation. Secondary silyl alcohols are oxidized to aldehydes. 

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