Organolithiums electrophiles

The mechanism of organolithium addition to naphthyl oxazolines is believed to occur via initial complexation of the alkyllithium reagent to the oxazoline nitrogen atom and the methyl ether to form chelated intermediate 17. Addition of the alkyl group to the arena 7t-system affords azaenolate 18, which undergoes reaction with an electrophile on the opposite face of the alkyl group to provide the observed product 4. The chelating methyl... 

Recently, nitration of organolithiums and Gngnards v/iih has been developed for the preparation of certain kmds of nitro compounds fEqs. 2.14 and 2.15. The success of this process depends on the reaction conthdons (low remperanirei and the stnicnire of substrates. For example, 3-nitrothiophene can be obtained in 70% overall yield from 3-bromothiophene this is far superior to the older method. 3-Nitroveratrole cannot be prepared usefully by classical electrophilic nitradonof veratrole, but it can now be prepared by direct orr/io-lithiadon followed The mechanism is believed to proceed by dirutrogen rathcal, followed by the rathcal s combinadon. 

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. 

Organolithium reagent 35 was added to aldehyde 31 (Scheme 7.6) to obtain alcohol 36 as an inconsequential 1 1 mixture of diastereomers. The benzylic alcohol was removed using a Barton two-step radical deoxygenation protocol, followed by electrophilic aromatic bromination to provide the desired coupling partner 37. 

Organolithium derivatives are strongly nucleophilic reagents, and their use in synthesis would be greatly increased if they could easily be converted to electrophilic reagents. Reversed reactivity of lithium derivatives would be... 

Lithiation of to form 184 was reported by the Harmata group to be the first example of a sulfoximine-stabilized vinyl carbanion. The resulting organolithium species 184 reacted with various electrophiles to supply structurally diverse benzothiazines <88TL5229>. However, the diastereoselectivity of the reactions with aldehydes was low (Scheme 48). 

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. 

In addition to the reactions discussed above, a,//-unsaturated oxazolines can also act as chiral electrophiles to undergo conjugated addition of organolithium reagent to give optically active / ,/ -disubstituted carboxylic acids.52 The vinyl oxazolines 48 are prepared using the two methods outlined in Scheme 2-27. 

Scheme 2.38 Functionalized allenes formed by 1,4-addition of organolithium reagents to enynes and electrophilic trapping with aldehydes (111, 112) ketones (113,114), ethylene oxide (115) and carbon dioxide (116).

Allenes are deprotonated by organolithium bases to yield allenyllithium intermediates. Subsequent treatment of these intermediates with various reactive carbon electrophiles can follow several pathways. An early study showed that terminal allenes bearing a free CH2 substituent afford mainly the direct SE2 substitution product A upon treatment first with BuLi and then with various unbranched alkyl iodides (Table 9.1) [5], A negligible amount of the SE2 propargylic product C was formed under these conditions Small amounts of regioisomeric allene alkylation products B were presumed to arise from 1,3-dilithioallenes. 

Some carbyne complexes, in particular cationic ones with good Ji-accepting ligands, can react with nucleophiles to give carbene complexes [187,521]. Several reductions of carbyne complexes to carbene complexes by treatment with metal hydrides have been reported. Similarly, organolithium or other carbanionic reagents can react with electrophilic carbyne complexes to yield carbene complexes. Illustrative examples of both reactions are sketched in Figure 3.23. 

In this chapter, we will emphasize these recent developments, especially those that allow the preparation of organocopper species not accessible through the standard procedures involving organolithiums as precursors and their use in reactions with organic electrophiles. 

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