Organolithium preparation

The second asymmetric intramolecular anionic cyclization was performed with a chiral a-amino organolithium, prepared by the Beak methodology [133]. Thus, the stannane 94... 

Table 6. Organolithiums Prepared from Organic Halides with Li Aromatic Radical Anions in THF...

Table 1 contains examples of organolithiums prepared by reaction (a). The preparation of CHjLi by this reaction proceeds too slowly to be usefuL. In addition to... 

Table 1. Organolithiums Prepared from Organomercurials with Li Metal ...

Examples of organolithiums prepared by reaction of Li metal with an acidic hydrocarbon are presented in Table 1, along with those that form high yields of reduced dimeric substrate as byproducts. This procedure forms low yields of (CgH5)3CLi, and (CgH5)2CH2 fails to react with Li in DME. For practical purposes, therefore, the reaction should be attempted only with a hydrocarbon that has a pK < 30. 

The organolithiums prepared by the cleavage of phenyl sulfides are contaminated with LiSCgHj, which may affect their reactivity. In synthetic reactions, however, the byproduct QHjSH, which has a pK, of 6.5, is removed. 

CH3)2N]3P0. M.p. 4°C, b.p. 232"C, dielectric constant 30 at 25 C. Can be prepared from dimethylamine and phosphorus oxychloride. Used as an aprotic solvent, similar to liquid ammonia in solvent power but easier to handle. Solvent for organolithium compounds, Grignard reagents and the metals lithium, sodium and potassium (the latter metals give blue solutions). 

It is sometimes necessary e.g., in reactions involving organolithium compounds or in certain Grignard preparations) to carry out a reaction... 

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 ... 

Another example illustrating the greater reactivity of organolithium compounds is the preparation of the otherwise difficultly accessible esters of 2-pyridyl-acetlc acid by the following series of reactions from a-picoline ... 

Many organic halides do not react satisfactorily with lithium to form RLi ecMnpounds or with metallic magnesium to form Grignard reagents. The desired organolithium compound can often be prepared by a halogen-metal interconversion reaction ... 

As pointed out in Note 1 a nitrogen atmosphere is preferred for the preparation of organolithium compounds. In the present example exclusion of oxygen is attained fairly satisfactorily by keeping the solution at the reflux point throughout an atmosphere of ether vapour is thus maintained. 

Several groups have developed procedures for Pd-mediated coupling based on this general chemistry. The variety of such procedures and the range of compounds for which they are applicable suggest that Pd-calalysed coupling is currently the most versatile method for introduction of 2-substituents which cannot be prepared directly from organolithium intermediates. 

Carbocyclic substitution can also be achieved by first introdueing a reactive organomelallic substituent. Preparation of organolithium reagents can be done by one of the conventional melhods. especially halogen-metal exchange or directed lithiation. Table 14.2 gives examples. 

If the organolithium derivative of 2.4-dimethylthiazole or 2-methyl-4-phenylthiazole (prepared at -78°C) is allowed to warm to room temperature, the 2-lithium compound reacts with the nonmetallated thiazole (Scheme 5) (225). 

Before we describe the applications of organometallic reagents to organic synthesis let us examine their preparation Organolithium compounds and other Group I organometal he compounds are prepared by the reaction of an alkyl halide with the appropriate metal... 

Grignard reagents (Section 14 4) Grignard reagents are prepared in a manner similar to that used for organolithium compounds Di ethyl ether and tetrahydrofuran are appro priate solvents... 

RM can be a traditional Grignard reagent or an organolithium, 2inc, aluminum, or mercury compound. The Grignard route is employed commercially for production of tertiary phosphines, even though these reactions are subject to side reactions. Yields are often low, eg, 40—50% for (C4H )2P prepared via a Grignard reaction (18). A phosphoms—carbon bond can form from the metathetical reaction of a phosphoms haUde and a pseudohaUde salt. 

R Tl compounds, eg, methyl [3003-15-4], ethyl [687-82-1], isobutyl [3016-08-8], and phenyl [3003-04-1] thaHium(III), are usuaHy prepared by the reaction between a dialkyl or diarylthaHium haHde and an organolithium reagent in ether (16) ... 

Organolithium and organosodium reagents can also be used to prepare tetraorganotins ... 

This complex should be used when the organolithium is in solution in a hydrocarbon solvent. For organolithium reagents prepared in ether (see Note 4), the same complex may be used or, more conveniently, copper iodide (Cull can be used. The Cul purchased from Prolabo or Merck 4 Company, Inc. may be used directly. Other commercial sources of Cul (Fluka, Aldrich Chemical Company, Inc., Alfa Products, Morton/Thiokol, Inc.) furnish a salt which affords better results when purified. 1 mol of Cul is stirred for 12 hr with 500 ml of anhydrous tetrahydrofuran, then filtered on a sintered glass funnel ( 3), washed twice with 50 ml of anhydrous tetrahydrofuran, once with 50 ml of anhydrous ether and finally dried under reduced pressure (0.1 imO for 4 hr. 

OrganometalUc reagents, prepared from fluorohalocarbons, including Grig-nard reagents [52] or organolithium reagents prepared by transmetaUation [50], are silylated with readily a variable alkylchlorosilanes (equations 70 and 71). 

Heptafluoro-2-naphthyllithiuni prepared by metalation reaction can thermally decompose to a hexafluoro-l,2-naphlhalyne by elimination of lithium fluoride [36, 37] In this organolithium compound, fluorine elimination can occur from either position 1 or 3, however, no evidence for fluorine elimination from position 3 IS observed... 

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