Aryllithium preparation

Table 4. Aryllithiums Prepared from Aryl Halides with Li Metal...

The sesquiterpenoid hydrocarbons (5)-a-curcumene (59) and (5)-xanthorrhizol (60) were prepared by asymmetric conjugate addition of the appropriate aryllithium reagent to unsaturated oxazoline 56 to afford alcohols 57 (66% yield, 96% ee) and 58 (57% yield, 96% ee) upon hydrolysis and reduction. The chiral alcohols were subsequently converted to the desired natural products. ... 

It should also be noted that the 5-exo-trig cyclization of achiral olefinic organolithiums has been found to proceed enantioselectively when conducted in the presence of a chiral ligand that serves to render the lithium atom stereogenic. Thus, for example, R) 1 -allyl-3-methylindolinc has been prepared in 86 % ee by cyclization of an achiral aryllithium in the presence of an equivalent of (-)-sparteine.15... 

Organometallic compounds can be hydrolyzed by acid treatment. For active metals such as Mg, Li, and so on, water is sufficiently acidic. The most important example of this reaction is hydrolysis of Grignard reagents, but M may be many other metals or metalloids. Examples are SiRs, HgR, Na, and B(OH)2- Since aryl Grignard and aryllithium compounds are fairly easy to prepare, they are often used to prepare salts of weak acids, for example,... 

Unsymmetrical coupling of vinylic, alkynyl, and arylmercury compounds was achieved in moderate-to-good yields by treatment with alkyl and vinylic dialkylcopper reagents (e.g., PhCH=CHHgCl -t- Mc2CuLi PhCH=CHMe). Unsymmetrical biaryls were prepared by treating a cyanocuprate ArCu(CN)Li (prepared from ArLi and CuCN) with an aryllithium Ar Li. ... 

A variation of an approach developed by Meyers was used to prepare nifedipine-type 1,4-dihydropyridines 35 from pyridine 34 using an oxazoline-directed aryllithium 1,4-addition reaction <96H(43)2425>. 

Arylcopper intermediates can be generated from organolithium compounds, as in the preparation of cuprates.95 These compounds react with a second aryl halide to provide unsymmetrical biaryls in a reaction that is essentially a variant of the cuprate alkylation process discussed on p. 680. An alternative procedure involves generation of a mixed diarylcyanocuprate by sequential addition of two different aryllithium reagents to CuCN, which then undergo decomposition to biaryls on exposure to oxygen.96 The second addition must be carried out at very low temperature to prevent equilibration with the symmetrical diarylcyanocuprates. 

The most straightforward synthesis of compounds (L)AuAr uses the metathesis of (L)AuX precursors with aryllithium reagents, as, for example, executed for the preparation of (Ph3P)AuPh. The crystal structure of this benchmark complex has been determined. The linear coordination geometry is as expected. No aurophilic contacts are discernible in the crystal packing. Short Au- -Au contacts are observed, however, in the dinuclear compound (dppm)(AuPh)2 with an intramolecular intermetallic distance of 3.154(1) A. This complex shows a UV-VIS absorption at 290-300 nm and is luminescent in fluid solution at room temperature.1... 

An aryllithium reagent, prepared from 1-bromo-2,6-diethylbenzene and butyllithium, reacts with SnCl2 in THF at 0°C to produce hexakis(2,6-diethylphenyl)tristannacyclopro-pane, 47, in 50-55% yield883. If the reaction above is performed at 0°C in Et20, the 1-butyl-2,2,3,3,4,5,5,6,6-nonakis(2,6-diethylphenyl)hexastannabicyclo[2,2,0]hexane, 48, can be isolated in 1.5% yield. This compound turns out to be the first example of a polycyclic polystannane88b. 

The reagent is prepared by reaction of (Cp2ZrCl)20 with A1(CH3)3 (75% yield).1 Benzyne zirconocene complexes.1 This reagent reacts with an aryllithium at - 50° to form an intermediate a that loses methane at 25° to give a zirconocene... 

Eight Al(Por)R complexes (For = OEP,TPP R = Me, "Bu, CeHs, C6F4H) were prepared from the reaction of Al(Por)Cl with an alkyl or aryllithium reagent. Mass spectra of the compounds showed low intensities for the molecular ion peaks, consistent with facile cleavage of the Al—C bond. The chloride complexes Al(Por)Cl show normal porphyrin UV-visible spectra, whereas the organometallic complexes Al(Por)R show a split Soret band typical of hyperporphyrin spectra. 

In contrast, tellurium insertion in alkyl- or aryllithium compounds followed by alkylation is a useful method for the synthesis of unsymmetrical tellurides. (For a tabulation of unsymmetrical tellurides prepared by alkylation of organyl tellurolates, see ref. 8.)... 

The preparation of aryllithium reagents can also be performed by using t-butyllithium in a halogen-metal exchange, and aqueous potassium ferricyanide as an oxidant. 

Other compounds of the type Ln(CsH5) 2R are known where R is an alkyl or aryl group. These include —C=C 120), —, and —CH3 121). They are prepared from (C5H5)2LnCl and alkyl- or aryllithium. These complexes also are reported to show a decrease in at liquid nitrogen temperatures. 

Various commercially available compounds containing C—Li bonds are listed in Table 1. The alkyllithium and aryllithium species listed there are usually very reactive. These compounds serve to prepare in situ other intermediate reagents. These proceedings may afford various advantages in organic synthesis, such as better control of the reaction path, increased stereochemical selectivity and the possibility of working at higher temperatures. 

TABLE 6. Aryllithiums Li—R carrying amino and alkoxy substituents prepared in diethyl ether by metal insertion into the corresponding bromoarene... 

The preparation of functionalized aryllithium compounds bearing an oxygen- or sulfur-containing functionality in a benzylic position is also possible by arene-catalyzed lithiation. When chlorinated materials 239 were deprotonated (for Y = OH, SH) with n-butyllithium in THF at —78 °C and then lithiated using DTBB as the catalyst at the same temperature. 

The functionalized arylzinc reagents are best prepared either starting from an aryllithium obtained by halogen-lithium exchange followed by a low-temperature (-80°C) transmetalation with ZnBrj or by performing an iodine-magnesium exchange reaction. The latter reaction tolerates temperatures up to -30°C and is more convenient for industrial applications. ... 

Bidentate ferrocene ligands containing a chiral oxazoline substituent possess both planar chiral and center chiral elements and have attracted much interest as asymmetric catalysts.However, until recently, preparation of such compounds had been limited to resolution. In 1995, four groups simultaneously communicated their results on the asymmetric synthesis of these structures using an oxazoline-directed diastereoselective lithiation (Scheme 8.141). " When a chiral oxazolinylferrocene 439 was metalated with butyllithium and the resulting aryllithium species trapped with an electrophile, diastereomer 442 was favored over 443. The structure of the major diastereomer 442 was confirmed, either by conversion to a compound of known stereochemistry or by X-ray crystallography of the product itself or of the corresponding palladium complex. ... 

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