Dilithio compounds

If two equivalents of the reagents are used, disubstitution to ECeC-CH(E)R occurs in most cases, but interestingly the reaction of LiCeCCH(Li)R with an excess of COj gives mainly the allenic dicarboxylic acids. These are probably the result of a rapid isomerization of the primary dilithium salt of the acetylenic diacid during the work-up or during the reaction of the dilithio compound with COj ... 

The low yield of the diacid may be explained by incomplete carboxylation, due to the slight solubility of the dilithio compound. 

The dichloro derivative 4, together with the ten-membered ring compound 5, is formed from the dilithio compound 3 by successive treatment with sulfur and sulfur dichloride.413... 

A solution of the dilithio compound 3. prepared from 2.5-dichloro-3,4-diiodothiophene (4.85 g, 12 mmol) and 1.6 M BuLi in hexane (15mL. 24 mmol), in Et20 (100 mL) was stirred under N2 at — 95 C and sulfur (0.77 g. 2 equiv) was added. The mixture was allowed to warm to — 20 C and was slowly treated with SC12 (1,236 g, 12 mmol). After 15 min, H20 (50 mL) was added, the organic layer was separated, dried and evaporated and the residue was chromatographed (alumina) to give the product as pale-yellow needles mp 126 C. (The yield was not reported.)... 

However, the reaction of (lZ,3Z)-l,4-dilithio-l,3-butadiene (36) with phenylantimony dichloride (Scheme 5) affords 1-phenylstibole (37),14 which has been converted to l.l -distibaferrocene (9).15 Unfortunately, there is no totally satisfactory synthetic route to dilithio compound 36. Sn/Li exchange of (lZ,3Z)-l,4-bis(trimethylstannyl)-l,3-butadiene (38) with methyllithium gives a good yield of 36, but the preparation of 38 is... 

One of the most interesting reactions of this type involves the intramolecular addition of the organolithium derivative to the aryne (13) which is derived from the dilithio-compound (12) 28>. This leads to the remarkably stable organolithium compound (14) which reacts with water to form the expected heptafluorobiphenylene, and with bromine to form 1-bromoheptafluorobiphenylene. 

The reaction of benzyne with furan was the first example of a Diels-Alder reaction of benzyne to be studied b. No authenticated examples of arynes are known which fail to give cyclo-adducts with furan i38>. The tetrahalogenobenzynes all form the expected adducts 103, X = F 6), Cl 57>i39)j gr 59) or i 59)). d0 other highly fluorinated arynes i40,i4i>. The isomeric adducts (104) and (105) have been detected by 19F n.m.r. spectroscopy when the dilithio-compound (12) was allowed to decompose in the presence of furan 28 103). 

Attempts to isolate 1,3-dilithiated propargylic ethers with two equivalents of BuLi at temperatures above -20 give unsatisfactory results, because the dilithio compounds are unstable. In the case of HCsCCH2Or-Bu, HCsCCH(-f-Bu)OH is found after aqueous hydrolysis, possibly as a result of a Wittig-rearrangement [2]. At temperatures below -20 C the dilithiation is too sluggish to be of practical interest. With the super-basic reagent BuLi.t-BuOK in a THF-hexane mixture dipotassiation can be effected in a relatively short time at low temperatures. 

By comparison with the known values of optical rotation the configuration at C-3 of the predominant enantiomer of the 3-phenylalkanoic acid was R in most cases (CIP rules dependent). Therefore, a bicyclic structure of the dilithio compound, in analogy to that proposed for the deprotonated 3-phenyl-2-propenyl ether21, which is alkylated in a metalloinversive reaction mode seems to be reasonable. 

For formation of 1,2-dilithio compounds and 1.2-di-Grignard reagents, but not by this method, see van Eikkema Hommes Bickelhaupt Klumpp Reel. Trav, Chim. Pays-Bas 1988, 107. 393. Angew. Chem. Ini. Ed. Engl. 1988, 27. 1083 [Angew. Chem. 100, 1100],... 

Dimethoxyfuran can be mono- and di-lithiated and the intermediates undergo conventional reactions (78HCA430). Furan-2-carboxylic acid on treatment with LDA in THF at -78 °C for 0.5 h yields the dilithio compound (402), which is stable up to -10 °C above this temperature, proton abstraction from THF occurs. It reacts smoothly with both chlorotrimethylsilane and iodomethane at -78 °C (Scheme 115), but other alkylations... 

Dilithiation of dicyclopropylacetylene was best effected with 5-fold excess of f-BuLi-TMEDA complex. Quenching of the separable dilithio compound with electrophiles gave the corresponding disubstituted dicyclopropylacetylenes (equation 164)239. 

Metallation of 4,4 -, 5,5 -, 6,6 -, and 7,7 -dibenzo[6]thienyl with two molar equivalents of n-butyllithium affords the corresponding 2,2 -dilithio compounds, which give the corresponding 2,2 -dicarb-oxylic acids on carbonation.517... 

The cleavage of a Si—Si bond in silacyclic compounds by lithium metal is the most versatile method to prepare linear, a, -dilithiated oligosilanes. The first dilithio compound obtained by Gilman and coworkers in this way was Li(Ph2Si)4Li (equation 29)72. 

In sharp contrast to the aforementioned lithiated (amino)arylsilanes, 1,3-dilithio compounds 30, which were prepared from the corresponding chlorosilanes 29 by treatment with lithium naphthalenide (equation 42), decompose completely after 3 h at 0 °C91. 

Treatment of 3,4-diethynylsilole 29 with 2 equivalents of lithium diisopropylamide, followed by the reaction of the resulting dilithio compound with 1,2-dichlorotetramethyl-, 1,2-dichlorotetraethyl- or 1,2-dibutyl- 1,2-dichlorodimethyldisilane produces the cyclic silole derivatives 11843 (Scheme 29). 

As an alternative to condensation of dichlorosilanes by alkali metals, it is possible to synthesize poly silanes by the reaction of preformed dilithio compounds with dichlorosilanes. An early synthesis of a copolymer by this route is illustrated in equation (19).10 (see also Section 5.9.2). Finally, poly(phenylmethylsilylene) has been made by thermal decomposition of a silyl-mercury polymer36 (equation (20)). 

The chemistry of 1,8,10,9-triazaboradecalin, 7, has been explored in considerable detail. The 1,8-dilithio compound is readily accessible 22> and offers interesting preparative aspects. Originating from the dilithio compound, the novel heterocyclic systems 72 80> and 13 22> have been... 

Diketones react diastereoselectively with the dilithio compounds 475 obtained by the ortho and a-directed metallation of alkyl aryl thioethers and sulfones to give the fra r-thiochroman-3,4-diols and their 1,1-dioxides (Scheme 166) <1998S1098>. o-Bromophenyl sulfones 476 yield the 3,4-disubstituted thiochroman dioxide by a radical cyclization the trans isomer is the predominant or even exclusive product (Equation 160) <1995SL943>. 

Sequential iodine lithium exchange from the 1,5-diiodonaphthalene 63 generates either the monoiodo-monolithio species 64 or the dilithio species 65.70 Clean monolithiation is obtained by allowing the initially formed mixture of mono- and dilithiated products to equilibrate with unreacted starting material over a period of 6 h at 5 °C. No equilibration is necessary on the second lithiation, which is complete in 1 h at -78 °C. 1,8-Diiodonaphthalene 66 can similarly be converted to the dilithio compound 67.71... 

Aromatic dibromides (1,2-dibromobenzene, 1,4-dibromobenzene, 1,2-dibromo-6-methoxybenzene, 2,7-dibromo-3,6-dimethoxynaphthalene, 5,10-dibromoanthracene) can be converted to lithioaryl bromides and subsequently to lithium bromoarenetellur-olates (Table 1 p. 155). An example of such a reaction sequence is given for 1,4-dibromobenzene3-4. With four moles of tert.-butyl lithium per mole of dibromoarene, the dilithio compounds that were formed were converted to the ditellurolates4 (Table 1 p. 155). 

This volume, which complements the earlier one, contains 9 chapters written by experts from 7 countries. These include a chapter on the dynamic behavior of organolithium compounds, written by one of the pioneers in the field, and a specific chapter on the structure and dynamics of chiral lithium amides in particular. The use of such amides in asymmetric synthesis is covered in another chapter, and other synthetic aspects are covered in chapters on acyllithium derivatives, on the carbolithiation reaction and on organolithi-ums as synthetic intermediates for tandem reactions. Other topics include the chemistry of ketone dilithio compounds, the chemistry of lithium enolates and homoenolates, and polycyclic and fullerene lithium carbanions. 

Deactivation of the amide carbonyl by N-lithiation directs the second lithiation to the ortho position to the amide group. The dilithio compound is stabilized by intramolecular chelation. Larcheveque and coworkers used a chiral amide that was obtained from the reaction between an optically active epihydrin and an anhydride for the asymmetric synthesis of ketones or of substituted acids76 (equation 13). 

Connect a Teflon tube between the two stirring solutions and transfer the solution of the dilithio compound of 10a into the borate ester solution by means of an overpressure of argon at -78°C. 

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