Lithium, bis

The reaction of the bis(trimethylsilyl)methylene-bridged bis(difluoro disilazane) (Me3Si)2C[SiF2(NHSiMe/-Bu2)]2 369 with 2 equiv. of methyllithium has produced the bis(trimethylsilyl)methylene-bridged bis(lithium difluoro... 

Bis(butyl tellurium)methyl sulphide, prepared from bis(bromomethyl)sulphide and n-BuTeLi by treatment with 2 equiv of n-BuLi, gives rise to the corresponding bis(lithium methylsulphide), which can be isolated under vacuum as a colourless powder and stored at -20°C for 6 months. It decomposes under argon at 60°C and ignites explosively upon contact with traces of air. 

The chiral base 360 turns out not to be the best choice for enantioselective lithiation of the sulphur analogue 437 (Scheme 177) the bis-lithium amide 438 in the presence of LiCl at — 100°C gives better yields and enantioselectivity The base 438 often turns out to be a good choice as an alternative to 360 for reactions that fail to give good enantioselectivity. ... 

An interesting result, contributed by Gibson (nee Thomas) and coworkers, should be added " The tricarbonylchromium complexes 258 are readily deprotonated by the chiral bis(lithium amide) 234 and alkylated to provide highly enantioenriched alkylation products 260 (equation 62). The decisive intermediate 259 presumably is formed by abstraction of the pro-S proton and is attacked from above. Related work has been published by Ewin and Simpkins . 

Chiral bis-lithium amide bases have been used for enantiotopic deprotonation of the sulfonium salt of 1,4-oxathiane 86. The anion undergoes an enantioselective thia-Sommelet rearrangement to afford the 3-substituted-1,4-oxathiane 87. Only bis-lithium amide bases were effective, giving products with high diastereoselectivity and with low to moderate enantioselectivity (Equation 13) <2003TL8203>. 

A similar sequence was reported where the asymmetry was introduced by the reaction of weio-3-substituted glutanc anhydrides and (S)-methylbenzylamines to give diastereomeric hemiamides that could be separated by recrystallization The asymmetnc desymmetrization of certain 4-aryl substituted glutanmides has also been accomplished with high levels of selectivity (up to 97% ee) by enolization with a chiral bis-lithium amide base. The selectivity of the reaction was shown to be the result of asymmetric enolization, followed by a kinetic resolution." ... 

Bis(trimethylsilyl)methylene-bridged bis(lithium difluoro silylamide), preparation, 3, 112 1-15 Bis(trimethylstannyl)calcium, preparation, 3, 859 Bis(triorganosilyl) diazene, preparation, 3, 445 Bis(triorganosilyl)silyl dianions, reactions, 3, 422... 

Bis-[lithium teUuro]-2,5-dimethylthiophene1 Under an inert atmosphere, 1 equivalent of 3,4-dibromo-... 

Alexakis and coworkers have developed several homochiral bis-lithium amides such as 13 and 101 (Scheme 70)19,m. Interestingly, efficient recycling of the chiral lithium... 

The synthesis of cyclic tetraselenadiynes could be achieved by a stepwise approach. Key steps were the reaction of the lithium salt of trimethylsilylacetylene 168 with a,ra-diselenocyanatoalkanes 169. By treating the bis-lithium salt of the resulting a,u -diselenaalkadiynes 170 again with 169, the cyclic tetraselenadiynes 172 resulted with methylene chains between the Se-C=C-Se units (Scheme 19) <2002JOC4290>. 

Bis-lithium species (45) reacts with hexafluorobenzene at adjacent carbons to form phenanthrene ring (46) in good yield (Scheme 2.7) [15]. 

Two complexes containing a dilithiated stilbene fragment have been prepared and isolated from the reactions of 1,2-diphenylethane with N-chelated butyl-lithium reagents. " The molecular and crystal structures of these compounds, stilbene bis(lithium tetramethylethylenediamine) (Figure 4a) and stilbene bis(lithium pentamethyldiethylenetriamine) (Figure 4b), have been determined by X-ray diffraction techniques. Each structure contains two amine-solvated Li atoms located above and below the olefinic bond of a stilbene molecule. The stilbene molecule is planar in both structures, and is in a trans configuration about the C(7)—C(7 ) bond, which is ca. 0.01 nm longer than that in trans-stilbene. " The optical and "C n.m.r. spectra of THF solutions of the related dilithium and disodium salts of tetraphenylethylene dianion, as well as the spectra of their mixtures, have been examined. " The data can be rationalized in terms of the... 

Figure 4 The molecular structures of (a) stilbene bis(lithium tetramethylethylenediamine) and (b) stiUiene bis(lithium pentamethyldiethylenetriamine)...

Bis(lithium di-wo-propylsilylindolide) reacts with two equivalents of difluorodimethylsilane with formation of a 16-membered macrocycle 12 (Scheme 8). 

C30H6sMOjOg, Hexakis(2,2-dimethylpropoxy)dimolybdenum, 43B, 1377 C3oH7oCl2Lii,Oi 2R 2 f Bis[ lithium pentaisopropoxo-oxorhenate(VI) lithium chloride tetrahydrofuran], 46B, 1143 C30H72Cl2PeNi2O1n, Hexakis(diethylurea)irondl) perchlorate, 46B, 1158... 

IMth diols, such as diisopropyl tartrate, BINOL, PhCH(OH)CH20H, and pinacol, the reaction of aUylSiCH can be controlled to generate the corresponding tetracoordinate Si species by replacement of two chlorides (eq 1). With less bulky diols, such as diisopropyl tartrate, the reaction can be extended to produce pentacoordinate Si(V) species (eq 1) allylSiF3 reacts in a similar way. Bis-lithium catecholate affords the pentacoordinate species.Vicinal amino alcohols and diamines, namely pseudoephedrine and fran5-l,2-diaminocyclohexane, generate tetracoordinated species (eq 2). 

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