Organolithium compounds electrophiles

Alkenyllithium compounds are intermediates in the Shapiro reaction, which is discussed in Section 5.7.2. The reaction can be run in such a way that the organolithium compound is generated in high yield and subsequently allowed to react with a variety of electrophiles.64 This method provides a route to vinyllithium compounds starting from a ketone. 

The relative rates for various organolithium compounds are para-tolyl > phenyl > ethyl > isopropyl. As for the ketone, the rate is enhanced by electron-withdrawing substituents which increase the coordinating power of the carbonyl carbon. It therefore appears that the crucial step is the electrophilic attack by the carbonyl on the group R of the organolithium compound. 

The intermediate organolithium compound 358 shown in equation 89 is sufficiently stable at low temperature to be determined by NMR spectroscopy. Its presence can also be deduced after quenching with an electrophile, separating and purifying the product 359 and characterizing its structure by physical methods, including IR, H and NMR spectroscopies and MS. ... 

If the alkenyllithium 43 is used as organolithium compound with 39, siloxyallyllithium reagents 44 are formed ". As example, the isomerization of the silyl(allyl)alkoxides 44 gives the corresponding lithio-(Z)-silyl enol ethers 45 which react with various electrophiles to give 46 (equation 17) . ... 

The intramolecular carbolithiation of 6-lithio-l-hexene (9) was studied after lithiation of 6-chloro-l-hexene (8) in the presence of a catalytic amount of DTBB (5%). At —78 °C the corresponding organolithium compound 9 is stable, giving the expected products 10 by reaction with different electrophiles. However, when the lithiation step was carried out at — 30 °C a cyclization reaction took place, so that a new organolithium intermediate 11 was formed, which reacted with the same electrophiles to give cyclic products 12 (Scheme 5). ... 

Another type of sp -hybridized S-oxido functionahzed organolithium compounds has been easily prepared from chloroacetic acid (149). After a double deprotonation with lithium diisopropylamide in THF at —78°C, a DTBB catalyzed (5%) hthiation in the presence of different carbonyl compounds as electrophiles at the same temperature followed by final hydrolysis afforded the expected S-hydroxy acids 151. The corresponding intermediate 150 was probably involved in the process (Scheme 54)" . 

Acyclic and cyclic sp -hybridized ketal-containing y-functionalized organolithium compounds can be generated using an arene-catalyzed Uthiation at low temperature. In the case of acyclic precursors 171 (R = H) it was necessary to lower the temperature to -90 °C in the Uthiation step under DTBB catalysis (4%) in order to avoid decomposition of intermediates 172. Final electrophilic substitution reaction of these intermediates with electrophiles occurred with retention of configuration at temperatures ranging between... 

Eunctionalized organolithium compounds, having a protected carboxylic acid functionality, can also be considered as masked lithium tris-homoenolates and were prepared by DTBB-catalyzed (5%) Uthiation of the corresponding )-chlorinated materials. Eor instance, compound 227 in THE at —78°C leads to the expected organoUthium intermediate 228, which reacts with a series of electrophiles present in the reaction medium... 

For aU the chiral intermediates above mentioned (253, 257 and 258) the reaction with prochiral electrophiles (aldehydes or differently substituted ketones) gave a c 1 1 mixture of diastereomers so, as occurred in other chiral functionalized organolithium compounds, the asymmetric induction is practically non-existent. 

Y = O) or —90°C (Y = NMe, S) gave the corresponding intermediates 427 resulting from a carbon-sulfur cleavage. Further reaction of these functionalized organolithium compounds with different electrophiles at the same temperature, followed by hydrolysis with water, yielded products 428 (Scheme 120) . 

The electrophile for the cyclization reaction of an a-amino-organolithium compound is not restricted to a terminal (or phenylthio-substituted) ahcene and examples have been reported using carboxylic amides, alkynes and allyhc ethers." " For example, Fautens and Kumanovic reported that treatment of the bicyclic stannane shown in Scheme 24... 

Recently, some examples of the dearomatizing cyclization of unstabilized a-amino-organolithium compounds have been reported. For example, Clayden and Kenworthy showed that cyclization onto an oxazoline-activated naphthalene ring gives a lithium azaenolate. Note the high diastereoselectivity of the subsequent electrophilic quench, which places the electrophile cis to the carbon-carbon bond formed in the cyclization step (Scheme 25). "... 

The organolithium compounds, formed by deprotonation of Af-benzylic-Af-Boc p-anisole carbamates, react with imines to yield tran5-4,5-disubstituted 1,3-imidazolin-2-ones in good yield and excellent stereoselectivity (Scheme 52). Benzaldehydes gave poor stereoselectivity, and the nse of imines as electrophiles is critical. The stereoselectivity can be explained by the transition states shown, in which the aryl and R substituents on the 4-membered ring are trans to one another. 

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