Primary alkyllithium compounds

Addition of a primary alkyl group to enolizable ketones can be performed using magne-sium-ate complexes . The additional presence of 2,2 -bipyridyl (1 equiv.) in the reaction mixture improves the yields. The ate complexes are prepared in situ from the corresponding Grignard reagents and alkyllithium compounds (equations 140 and 141). 

In 1950, Letsinger reported that carbonation of 2-lithiooctane, 15, prepared by exchange of (—)-2-iodooctane with s-butyllithium in petroleum ether at —70 °C, gave (—)-2-methyl-heptanoic acid21. However, after first warming the 2-lithiooctane solution to 0°C over 20 minutes the resulting carboxylic acid was racemic. This was the first observation that a secondary alkyllithium compound inverts much more slowly than does a primary RLi compound. 

It has been shown that metallation of diisopropyl phosphates derived from primary aliphatic alcohols, except methanol, takes place at the alkyl as well as the isopropyl group in a ratio which is strongly influenced by steric effects. It was proposed that short-lived alkyllithium compounds were configurationally stable up to — 50°C and rearrange, with retention of configuration, into the corresponding a-hydroxyphosphonates (phosphate-phosphonate rearrangement) (Scheme 21). ... 

Aryl—alkyl coupling. The reaction of aryl bromides with alkyllithium compounds in ether results mainly in halogen—metal exchange. However, when THF is used as solvent aryl bromides react with primary alkyUithiums (1 hr., 25°) to give the cross-coupled products in 50-70% yields ... 

Addition of primary aUcylmagnesium halides and alkyllithium compounds to nitroarenes leading to o -adducts is an irreversible process, and because of that, the Sj,jAr of halogens with these nucleophiles does not proceed. The o -adducts of these nucleophiles can be subsequently oxidized with a variety of oxidants [23]. The most convenient and efficient oxidant of these a"-adducts is a solution of KMnO in liquid ammonia added after formation of the adducts [24]. The reaction is a valuable method of nucleophilic alkylation of nitroarenes (Scheme 11.12). 

Iron-acyl enolates, such as 2, prepared by x-deprotonation of the corresponding acyl complexes with lithium amides or alkyllithiums, are nearly always generated as fs-enolates which suffer stereoselective alkylation while existing as the crmt-conformer which places the carbon monoxide oxygen anti to the enolate oxygen (see Section 1.1.1.3.4.1.). These enolates react readily with strong electrophiles, such as primary iodoalkanes, primary alkyl sulfonates, 3-bromopropenes, (bromomethyl)benzenes and 3-bromopropynes, a-halo ethers and a-halo carbonyl compounds (Houben-Weyl, Volume 13/9 a, p 413) (see Table 6 for examples). 

Among unsolvated organolithium compounds only the alkyllithiums are soluble in noncoordinating solvents such as alkanes and arenes. Their states of aggregation depend on the structure close to lithium. Thus primary, tertiary and secondary alkyllithiums, all unsolvated, assemble into respectively hexamers, tetramers and equilibrium mixtures of hexamers and tetramers. Most organolithium compounds dissolve in and coordinate with donor compounds such as ethers and tertiary amines. The actual structures depend critically on the nature of the donor. Thus, diethyl ether solvates tend to be mainly cubic tetramers (with some dimers) while THF favors mixtures of monomers and dimers. Tertiary vicinal diamines such as TMEDA and 1,2-di-Af-piperidinoethane, DPE, favor bidentated coordinated dimers. Finally, in the presence of triamines such as pentamethyl-triethylenediamine PMDTA and l,4,7-trimethyl-l,4,7-triazacyclononane TMTAN, many organolithium compounds form tridentately complexed monomers. 

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... 

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