Alkyl lithium reagents

Alkyltrifluorosilanes and disubstituted difluorosilanes are themselves quite reactive with nucleophiles such as lithium amide bases [102, 103 104], alkyl-lithium reagents [1051, Gngnard reagents [105], or alkoxides [105] (equations 82 and 83)... 

Grignard and alkyl lithium reagents were found to add to the carbonyl group of a tricyclic vinylogous amide. However, the same compound underwent the usual vinylogous reduction with lithium aluminum hydride (712). Grignard additions to di- and trichloroenamines gave a-chloro- and dichloroketones (713). 

These alkene isomers are separately available (4) by treatment of threo-S-trimethylsilyloctan-4-ol, prepared by reduction of the corresponding ketone with DIBAL in pentane at —120°C, with base or acid. The preparation of 5-trimethylsilyloctan-4-one itself illustrates three general procedures the addition of alkyl lithium reagents to vinylsilanes to generate a-lithiosilanes, the preparation of complex /5-hydroxysilanes, as diastereoisomeric mixtures, and the oxidation of such compounds to /8-ketosilanes... 

Similarly, the reaction of the parent thiirane dioxide, the 2-chloro- and 2,3-cis-dimethylthiirane dioxides with either Grignard or alkyl lithium reagents, has been studied extensively. The fair-to-good yields of the sulfinates (62) obtained (48-82%), accompanied by ethylene (or the corresponding alkenes for substituted thiirane dioxide), have been interpreted in terms of initial nucleophilic attack of the base on the sulfur atom as depicted in equation 17116. 

Group members further devised two additional methods (methods C and D, Fig. 4.15) leading to monoalkylation products. In the first, an alkyl lithium reagent is added to the aldehyde 5 (0.1 M in Et20, —78 °C). Upon disappearance of starting... 

Preliminary investigations into the generality of this synthesis of lactate-derived ketones using other alkyl lithium reagents including butyllithium and phenyllithium have not been as successful. Product mixtures were typically contaminated with significant amounts of both the tertiary alcohol and the starting ester. 

The tetraimidosulfate anion [S(NtBu)4]2 is obtained, as the dilithium derivative 61, by the reaction of S(NtBu)3 with two equivalents of LiM I Bu.175 The nucleophilic addition of sterically undemanding alkyl-lithium reagents, e.g., MeLi, to S(N Bu)3 produces the dimeric complex [(thf)2Li2 (NtBu)3SMe 2] (62).174 A, A -chelated complexes of the [MeS(NlBu)3] anion are obtained by the nucleophilic addition of Me2Zn or Me3Al to S(NlBu)3.176... 

The polarimetric method, in combination with the results of chemical correlation, made it possible to determine the optical purity of a range of chiral sulftnates (105-107), thiosulfinates (35,105), and sulfinamides (83) with the sulfur atom as a sole center of chirality. These compounds were converted by means of Grignard or alkyl-lithium reagents into sulfoxides of known specific rotations. This approach to the determination of optical purity of chiral sulfinyl compounds has at least two limitations. The first is that it cannot be applied to sterically hindered compounds [e.g., t-butyl /-butanethio-sulfinate 72 does not react with Grignard reagents]. Second, this... 

For synthetic purposes the cyanate ion is a promising reagent leading to amines in water and to carbamates in dcohol (Hartsuiker et al., 1971). Alkyl-lithium reagents may also function in nucleophilic photosubstitutions with aromatic partners containing suitable leaving groups (Shapiro and Tomer, 1968). 

Reactions of Organophosphazenes with Alkyl Lithium Reagents. 73... 

Use of an electron rich alkyl lithium reagent eliminates these side reactions by counterbalancing the electron withdrawing effect of N3P3X5 unit. This has been demonstrated with LiC(OR)=CH2 (Eqs. 36, 37) [179]. 

As pointed out earlier (Sect. 7.1), alkyl lithium reagents induce metal-hydrogen exchange reactions. This possibility was investigated first by Paddock and coworkers [266,227]. They have found that the anion generated by the reaction of methylphosphazene with n-butyl lithium interacts with electrophiles such... 

Alkyl lithium reagents react with the hydridophosphazenes to generate phosphazeno anions [241]. These anions undergo facile reactions with non-metal halides or alkyl halides to produce phosphazenes with the phosphorus... 

The lithiated benzylic ether prepared from 79 is a carbon nucleophile. Under boron trifluoride catalysis10 it attacks diepoxide 6. In the process, the alkyl lithium reagent adds in a stepwise fashion to diepoxide 6, whereby the first addition is significantly more rapid than the second.7 One thus obtains only the monoadduct 24... 

N-methyl pyrrole 2.34, thiophene, and furan can be metallated at the C2 position with alkyl lithium reagents. This position is more activated to deprotonation than the C3 position because of the electron-withdrawing inductive effect of the heteroatom. The nucleophilic 2-lithio species can then be reacted with various electrophiles, as in the preparation of 2.37, 2.38,... 

Isothiazoles and nitrogen-blocked pyrazoles can be deprotonated at the C5 position with alkyl lithium reagents, and the resultant carbanions quenched with a wide range of electrophiles, as in the preparation of 4.33 and 4.34. 

Halides have been carbonylated via conversion to organolithium compounds. In the presence of chlorotrimethylsilane (TMSC1), alkyl lithium reagents give alkanoyl trimethyl-silanes (equation 165) which are useful synthetic sources of the alkanoyl synthon924. 

Oxathiolanes and 1,3-dioxolanes containing a 2-phenyl substituent react with alkyl-lithium reagents to produce aryl alkyl ketones and alkenes (65JOC226). The mechanism of this reaction is discussed in Section 4.30.2.2.7. 

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