Organolithium compounds with ethers

Polar solvents such as ethers and amines react with organometallic initiators, as well as propagating polystyryl and polydienyl carbanions, to decrease the concentration of active centers [3, 44, 45]. The rate of reaction with ethers decreases in the order Li > Na > K. For example, dilute solutions of poly(styryl)lithium in THF at room temperature decompose at the rate of a few percent each minute. Alkyllithium initiators also react relatively rapidly with ethers the order of reactivity of organolithium compounds with ethers is tertiary RLi > secondary RLi > primary RLi... 

The presence of organolithium compounds in etheric solvents at temperatures above 0°C may lead to extensive decomposition of the solvent and solute a slow electron transfer side reaction of lithium naphthalene or sodium naphthalene with the THE solvent (equation 5) has been reported . The three isomeric forms of BuLi were shown to induce extensive decomposition of THE. The main path for this process is metallation at position 2 of THE, leading to ring opening and elimination of ethylene. An alternative path is proton abstraction at position 3, followed by ring opening. The presence of additives such as (—)-sparteine (24), DMPU (25), TMEDA and especially HMPA does not prevent decomposition but strongly affects the reaction path. ... 

If the alkenyllithium 43 is used as organolithium compound with 39, siloxyallyllithium reagents 44 are formed ". As example, the isomerization of the silyl(allyl)alkoxides 44 gives the corresponding lithio-(Z)-silyl enol ethers 45 which react with various electrophiles to give 46 (equation 17) . ... 

As described in Section II.A, the tandem sequence reaction of organolithium compounds with carbon monoxide followed by reaction with suitable electrophiles provides an useful tool for the preparation of diphenyldialkyl carbinols, and the reaction could be easily extended to produce substituted cyclic ethers in a one-pot synthesis. Thus, by carrying out the carbonylation of phenyllithium in the presence of conveniently substituted chloroalkyl bromides, Br(CH2)3+ Cl, at -78 °C, the oxo-lithiated intermediates 243 are obtained and cyclized to 244 by warming up the reaction mixture (Scheme 74)21. 

Many organolithium compounds may be prepared by the interaction of lithium with an alkyl chloride or bromide or with an aryl bromide in dry ethereal solution In a nitrogen atmosphere ... 

Organolithium reagents (Section 14 3) Lithi um metal reacts with organic halides to pro duce organolithium compounds The organic halide may be alkyl alkenyl or aryl Iodides react most and fluorides least readily bro mides are used most often Suitable solvents include hexane diethyl ether and tetrahy drofuran... 

The reaction of tnfluoromethyl-substituted A -acyl umnes toward nucleophiles in many aspects parallels that of the parent polyfluoro ketones Heteronucleophiles and carbon nucleophiles, such as enarmnes [37, 38], enol ethers [38, 39, 40], hydrogen cyanide [34], tnmethylsilylcarbomlnle [2,47], alkynes [42], electron-nch heterocycles [43], 1,3-dicarbonyl compounds [44], organolithium compounds [45, 46, 47, 48], and Gngnard compounds [49,50], readily undergo hydroxyalkylation with hexafluoroace-tone and amidoalkylation with acyl imines denved from hexafluoroacetone... 

Organolithium compounds are sometimes prepared in hydrocarbon solvents such as pentane and hexane, but nonnally diethyl ether is used. It is especially important that the solvent be anhydrous. Even trace amounts of water or alcohols react with lithium to form insoluble lithium hydroxide or lithium alkoxides that coat the surface of the metal and prevent it from reacting with the alkyl halide. Furthennore, organolithium reagents are strong bases and react rapidly with even weak proton sources to fonn hydrocarbons. We shall discuss this property of organolithium reagents in Section 14.5. 

Organolithium compounds can readily be prepared from metallic Li and this is one of the major uses of the metal. Because of the great reactivity both of the reactants and the products, air and moisture must be rigorously excluded by use of an inert atmosphere. Lithium can be reacted directly with alkyl halides in light petroleum, cyclohexane, benzene or ether, the chlorides generally being preferred ... 

J-Oxygen-functionalised sp3 organolithium compounds react with alkenyl-carbene complexes to generate the corresponding cyclic carbene complexes in a formal [3+3] process (see Sect. 2.8.1). In those cases where the organolithium derivative contains a double bond in an appropriate position, tricyclic ether derivatives are the only products isolated. These compounds derive from an intramolecular cyclopropanation of the corresponding cyclic carbene complex intermediate [89] (Scheme 83). 

The crystal structures of many organolithium compounds have been determined.44 Phenyllithium has been crystallized as an ether solvate. The structure is tetrameric with lithium and carbon atoms at alternating corners of a highly distorted cube. The lithium atoms form a tetrahedron and the carbons are associated with the faces of the tetrahedron. Each carbon is 2.33 A from the three neighboring lithium atoms and an ether molecule is coordinated to each lithium atom. Figures 7.2a and b show, respectively, the Li-C cluster and the complete array of atoms, except for hydrogen 45 Section 6.2 of Part A provides additional information on the structure of organolithium compounds. 

Elimination to yield alkenes can be induced thermally or by treatment with acids or bases (for one possible mechanism, see Figure 3.39) [138,206]. Less common thermal demetallations include the thermolysis of arylmethyloxy(phenyl)carbene complexes, which can lead to the formation of aryl-substituted acetophenones [276]. Further, (difluoroboroxy)carbene complexes of molybdenum, which can be prepared by treating molybdenum hexacarbonyl with an organolithium compound and then with boron trifluoride etherate at -60 °C, decompose at room temperature to yield acyl radicals [277]. 

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