Alkyllithium species

The enantiomerically pure chloromethyl complexes (-)-(/ )-9 and ( + )-(S)-9 (shown below as 10) can be converted to iron-alkyl complexes by treatment with sodium borohydride, Grignard reagents, or alkyllithium species, with no loss of enantiomeric purity16,17 (see also Houben-Weyl, Vol. 13/9 a, p 193). 

Silene-transition metal complexes were proposed by Pannell121 for some iron and tungsten systems, and such species were observed spectroscopically by Wrighton.122,123 Thus intermediates such as 33 have been proposed in the preparation of carbosilane polymers from hydrosilanes,124 both as intermediates in the isotope scrambling observed to occur in similar ruthenium hydride systems125 126 and in the 5N2 addition of alkyllithium species to chlorovinylsilanes.47... 

Terminal propargylic mesylates are converted to alkylallenylzinc compounds by reaction with lithiotrialkylzincate reagents (Scheme 9.32) [117]. The latter are formed in situ from dialkylzinc and alkyllithium species. Deuterolysis of the allenylzinc intermediates gave rise to deuterated allenes (Eq. 9.138). 

Stereoselective addition to carbonyl groups is a powerful tool in organic synthesis and has received a great deal of attention. Addition to imines can be equally as powerful, but has received much less attention. Denmark and co-workers first introduced the use of bis(oxazoline) ligands in the addition reactions of imines.The most successful ligand has been the modified bu-box ligand 182. This ligand was used both stoichiometrically and catalytically in the reaction between various imines and several alkyllithium species. Selected examples are summarized in Table 9.32 (Fig. 9.54). 

Treatment of the potentially electrophilic Z-xfi-unsaturated iron-acyl complexes, such as 1, with alkyllithium species or lithium amides generates extended enolate species such as 2 products arising from 1,2- or 1,4-addition to the enone functionality are rarely observed. Subsequent reaction of 2 with electrophiles results in regiocontrolled stereoselective alkylation at the a-position to provide j8,y-unsaturated products 3. The origin of this selective y-deproto-nation is suggested to be precoordination of the base to the acyl carbonyl oxygen (see structures A), followed by proton abstraction while the enone moiety exists in the s-cis conformation23536. 

HAY et al (12, 13) showed that the addition of TMEDA to butyl-lithium (BuLi) produces a remarkable increase in reactivity toward the polymerization of butadiene. This higher reactivity is attributed to the absence of association of alkyllithium species and the presence according to the maximum rate of polymerifcftr-tion, of a separated ion pair during the polymerization. ERUSSALIMSKY et al(14) described the anionic polymerization of isoprene in the presence of TMEDA. They showed that the tertiary diamine causes a significant increase of the polymerization rate and of the content of 3,4-links in the polymers formed, a plateau being reached for r = TMEDA/living species =4. 

Stars of the type A2B2 were also prepared by the method developed by Quirk et al. In this case A was PS and B PI or PB [38,39]. Stars of the type A2(B-h-A)2, where A was PS and B PB were also synthesized by this method. The disadvantages of the method have already been mentioned. In order to overcome these problems the reaction of the living PS chains with the divinyl compound were monitored by SEC and UV spectroscopy, by observing the increase in absorbance of the diphenyl alkyllithium species at 438 nm. It is obvious that the method is very demanding experimentally and a lot of effort has to be exercised for the preparation of well defined products. 

The first total synthesis of the Stemona alkaloid (-)-tuberostemonine was accomplished by P. Wipf and co-workers. " The installation of the butyrolactone moiety commenced with the preparation of a Weinreb s amide from a methyl ester. The tricyclic methyl ester substrate was exposed to A/,0-dimethylhydroxylamine hydrochloride and Me2AICI and the tertiary amide was isolated in excellent yield. Next, the bromo ortho ester was treated with LDBB in THF to generate the corresponding primary alkyllithium species, which cleanly and efficiently added to the Weinreb s amide to afford the desired ketone. 

Moving away from alkyllithium species, Scheme 2.9.2 illustrates the use of lithium acetylide derivatives as useful nucleophiles for the formation of C-glycosides. As described by Lancelin, eta/.,133 lithium acetylides were added to... 

Alkyllithium species are good bases and a common use is the abstraction of a more-acidic proton. For example, addition of -butylhthium to a solution of diisopropylamine in THF gives hthium diisopropylamide (LDA), a common base. Abstraction of a more-acidic proton attached to a carbon atom can also be effected with n-butyllithium, or with stronger bases such as xec-butylUthium [EtCH(Me)Li], tert-butyllithium or the complex formed between -butyllithium and potassium tert-butoxide (t-BuOK). 

In addition to their basic properties, organolithium species can act as powerful nucleophiles in carbon-carbon bond-forming reactions. The synthetic utility of organolithium reagents can, however, be limited by the ease with which alkyllithium species act as a base. Despite this, alkyllithium species are well known to act as nucleophiles with a range of electrophiles, including aldehydes, ketones. 

Reductive Metalation. The powerful reductive nature of this reagent makes it an important tool for lithium-heteroatom exchange reactions. Thus, it was established early on that (phenylthio)alkanes can be converted into their requisite alkyl-lithium species. This has become the method of choice over generation by lithium metal alone. The resultant alkyllithium species can either be quenched with a proton source (eq 1), or intercepted with an electrophile. This has subsequently evolved into a powerful technique, since the reaction is general for all chalcogens (eq 2f and halides (eq 3). ... 

Scheme 10.51 Experimental evidence of trans selectivity in carbocyclization of the secondary alkyllithium species 154 [43].

The simplest view of the electronic structures of the tetrameric and hexameric alkyllithium species is one in which the bonding is considered in terms of localized multicenter bonding sites (13, 38). The structure of the tetramer will be discussed in detail, since the experimental data is most complete for this species. It is evident from inspection of Figs. 1, 2, and 3 that each lithium atom is associated with three alkyl carbon atoms. Assuming... 

Reaction scheme (it) is more likely than (i) on energy grounds. The dimer is probably an important species present in ether or triethylamine solutions of n-alkyllithium compounds, and might therefore reasonably be expected to function as a reactive intermediate in hydrocarbon solution. Rather complex kinetics should follow from scheme ( ), because various concurrent equilibria between alkyllithium species (e.g., between tetramer and hexamer, tetramer and tetramer, etc.) would be in effect. 

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