Butyllithium as a base

The TOSMIC anaiog -(tosyl)benzyl isocyanide readily reacts with simple acceptors (ethyl acrylate, acrylonitrile, etc.) to give 4-substituted 2-arylpyrroles. Extension to 2,3-diaryl derivatives by use of styryl acceptors required the use of n-butyllithium as a base. <95SC795>... 

Generation of cyclic organothio(sulfonyl)carbenes which undergo addition to nucleophilic al-kenes to give spiro-products 2, require the use of butyllithium as a base. ... 

Alkylation Reactions. Alkylation of chloromethyl /i-tolyl sulfone with alkyl halides can be effected either by using a pbase-transfer catalyst or butyllithium as a base (eqs 4 and 5). /t-Tolylsulfonylcbloromethylmagnesium, prepared by the reaction with ethylmagnesium bromide, is stable and undergoes normal Grignard reactions, e.g., carbonylation and carbonyl addition reactions. ... 

When butyllithium is used as a base it abstracts a proton in this case a proton attached to nitrogen The source of lithium diethylamide must be diethylamine... 

Because carbonyl compounds are only weakly acidic, a strong base is needed for enolate ion formation. If an alkoxide such as sodium ethoxide is used as base, deprotonation takes place only to the extent of about 0. l% because acetone is a weaker acid than ethanol (pKa - 16). If, however, a more powerful base such as sodium hydride (NaH) or lithium diisopropylamide ILiNO -CjHy ] is used, a carbonyl compound can be completely converted into its enolate ion. Lithium diisopropylamide (LDA), which is easily prepared by reaction of the strong base butyllithium with diisopropylamine, is widely used in the laboratory as a base for preparing enolate ions from carbonyl compounds. 

Reaction of a-sulphinyl carboxylic esters 421 with carbonyl compounds has usually been performed using a Grignard reagent as a base. No condensation products are obtained using t-butyllithium or sodium hydride367,496,497 (equation 251). The condensation products formed are convenient starting materials for the synthesis of a, p-unsaturated esters and /1-ketones497. 

Polystyrene-bound benzaldehydes can be smoothly olefinated with benzyl- or cin-namylphosphonium salts in DMF or THF using sodium methoxide as a base (Entry 1, Table 5.5 [64-67]). Alkylphosphonium salts, however, only react with resin-bound aldehydes upon deprotonation with stronger bases, such as butyllithium [30,68-70]. The more acidic acceptor-substituted phosphonium salts, on the other hand, even react with resin-bound aldehydes and ketones upon treatment with tertiary amines, DBU, sodium ethoxide, or lithium hydroxide [71-75], but stronger bases are also used occasionally [76]. 

Similarly, iV-silylmethylbenzotriazole derivatives have been prepared, using in this case n-butyllithium as the base and various electrophiles including cyclohexenone. Even alkylation of RSMA-type benzotriazole derivatives can be performed, leading to a new class of SMA (R2SMA).157... 

Diaza[12]coronand-4 (21) was condensed with diethylene glycol bismesylate 22 in the presence of butyllithium. Precipitation, occuring during the reaction course, afforded the proton cryptate 24 H+ c= [1.1.1] in 40% yield. It should be noted that [1.1.1] was obtained only in 10% yield via the high-dilution method 23). Lithium promoted cyclization was excluded (as an alternative mechanism) by an additional experiment in which KH served as a base instead of BuLi. Identical yield was achieved, indicating that intramolecular hydrogen bonding was responsible of the cyclization. 

Lithium diisopropylamide (LDA) is easily prepared by reaction between butyllithium (BuLi) and diisopropylamine and is widely used as a base fo preparing enolate ions from carbonyl compounds. LDA has nearly ideal] properties ... 

Charge stabilisation of the anion, which is formed after deprotonation, is still important, but to a lesser extent than when the acid/base reaction is reversible. If butyllithium is used as a base, then very unreactive hydrogens may be removed, which result in unstabilised anions. However, the conjugate acid is butane, which is a very, very weak acid also, as it is a gas, it leaves the reaction vessel. Thus, if butyllithium is used, the deprotonation becomes effectively irreversible. 

Propargylic alcohols. Butyllithium serves as a base and a nucleophile in the three-component reaction, also involving a terminal acetylene and an 7Y,A(-disubsti-tuted amide. 

Butyllithium reacts with cyclohexanone as a nucleophile rather than as a base. ... 

In Chapter 23, we introduced the idea that the last-formed anion in any dianion or trianion is the most reactive. Methyl acetoacetate is usually alkylated on the central carbon atom because that is the site of the most stable enolate. But methyl acetoacetate dianion—formed by removing a second proton from the usual enolate with a very strong base (usually butyl-lithium)—reacts first on the less stable anion the terminal methyl group. Protonation of the more stable enolate then leads to the product. Butyllithium can be used as a base because the anionic enolate intermediate is not electrophilic. 

The S n2 reaction product, p-aminoesters 372, produced from the reaction of allyl bromide 371 and arylamine by treatment with triethylamine, could be converted into substituted p-lactams in the presence of base. Conventional bases such as ethylmagnesium bromide, -butyllithium, potassium tert-butoxide, lithium hydroxide and potassium hydroxide used in such cyclizations failed to give p-lactam 373. However, Sn[N(TMS)2]2 as a base in the cyclization of p-aminoesters could successfully cyclize 372 to give p-lactam 373 (Scheme 4.120). Under optimized cyclization conditions, it was found that 1.5 equiv. of Sn[N(TMS)2]2 in toluene under reflux for 6 h achieved the best yield (up to 83%.)... 

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