Intermediates organolithium reactions

Finally, Azzena reported on the reductive functionalization of hexahydio-oxazolo[3,4- ] pyridine 193 its reaction with potassium or lithium and naphthalene followed by trapping of the intermediate organolithium derivative allowed for the isolation of piperidine 194 with useful levels of selectivities (Scheme 55) <2002J(P1)360>. 

An extension of the Barbier reaction to carboxylates salts [90] affords a simple access to furanyl ketones [91]. By sonication of a mixture of a lithium carboxylate, an alkyl chloride and lithium in THE at room temperature, the intermediate organolithium reagent forms rapidly, then generates the 2-furanyl lithium which adds to the carboxylate group in high yields. The method constitutes an example of a reaction cascade , in which several intermediates are generated sequentially (Scheme 3.13). 

N-Allyl tertiary amides 72 can be lithiated with r-BuLi and, like the secondary amides 54 and 57 they react y to nitrogen to give cis acylenamine products 74, with the intermediate organolithium adopting a structure approximating to 72.152 The stereochemistry of the reactions of lithiated allyl amides and carbamates in the presence of (-)-sparteine53 is discussed further in chapter 6. 

The lithiation and silylation of the amide 71 is enantioselective for a very different reason. When the intermediate organolithium is made from the racemic stannane 72, it still gives the product 74 in good enantioselectivity provided the electrophile reacts in the presence of (-)-sparteine.72 The reaction must therefore be an enantioselective substitution. Furthermore, reaction of the deuterated analogue 75 gives a result which is not consistent with asymmetric deprotonation yield, deuterium incorporation and product ee are all high. 

The 2-ethylanilide 76 may be laterally lithiated with s-BuLi and quenched with Me3SiCl to give the silane 78. The product is formed in 82% ee if the racemic intermediate organolithium 77 is first treated with (-)-sparteine at -25 °C and then Me3SiCl at -78 °C the reaction is an asymmetric substitution, with (-)-sparteine governing the enantioselectivity of the electrophilic quench step. But how does it do this ... 

The ester was cleaved by reduction with DIBAL (Ml AlH) and an achiral version of the normal protecting group put in place. It would obviously be silly to create unnecessary diastereo meric mixtures in these reactions. Then the tin could be exchanged first with lithium and then with an elec-tuophile, even an alkyl halide, with retention of configuration and without loss of enantiomeric purity. The intermediate organolithium compound must have had a stable configuration. 

Note that in several examples in Table 6.2 the initial adduct is used for subsequent reactions in situ. Peterson olefination [62] and related reactions (General Ref. [E], p. 27) have been performed via organolithium more than via organomagnesium intermediates, but reactions involving... 

Looking for a suitable preparation of dihydrobenzofuran derivatives by carbolithiation reactions, we have recently described how allyl 2-bromophenyl ethers 358 with a substituent at the a-position afford, after treatment with r-BuLi, addition of TMEDA and further quenching with electrophiles, functionalized fraws-2,3-dihydrobenzofuran derivatives 359 in a totally diastereoselective manner (Scheme 94)155. The key for the success of this reaction is the fact that intermediate organolithium 360 is not prone to undergo the 1,3-elimination process, probably due to the steric effect of the R substituent. The high diastereoselectivity of the ring closure could be explained by a transition state that accommodates the R group in a pseudoequatorial position. Moreover, simple allyl... 

Currently, the best route to phenyllithium-tricarbonylchromium is one in which the reaction between benzene-tricarbonylchromium and BuLi is conducted in 1 1 ethyl ether-tetrahydrofuran as the solvent system at —40°C for one hour. Under these conditions, carbonation gives benzoic acid-tricarbonylchromium in 61% yield, and the intermediate organolithium reagent has been used to form other functionally substituted derivatives of benzene-tricarbonylchromium in good yield (41, 42). 

In contrast, when this reaction was performed as a one-step process, on deuterolysis, products were obtained which suggested that an intermediate organolithium compound had been formed ... 

This reaction could be performed in wet technical grade solvent at room temperature although more of the halide then had to be used, presumably due to hydrolysis of intermediate organolithium compounds. 

Organozmc reagents are not nearly as reactive toward aldehydes and ketones as Grig nard reagents and organolithium compounds but are intermediates m certain reactions of alkyl halides... 

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... 

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