Bases Butyllithium-Sodium /-butoxide

While norbornene, norbornadiene, 2-triallkylsilylnorbornadiene, and 1,3,5-cycloheptatriene are selectively deprotonated by the LIC-NAOR mixture (butyllithium/sodium /f 7-butoxide), other less acidic substrates such as bicyclo[2.2.2]oct-2-ene, camphene, 3,3-dimethyl-l-butene, and tro/o-dicyclopentadiene require the use of stronger bases constituted by mixtures of pentylsodium/disodium pinacolate (NAC-NAOR) or pentylsodium/ potassium ftrt-butoxide (NAC-KOR). 

Isomerization of cis adducts of sulfenes with eneamines to trans adducts has been accomplished by treatment with n-butyllithium sodium methoxide or ethoxide, potassium t-butoxide, and triethylamine. " 7>-fl s-2,4-diphenyl-thietane 1,1-dioxide is converted to the cis isomer by treatment with sodium methoxide and equilibration of 2-methyl-4-phenylthietane 1,1-dioxide with bases gives mixtures containing 68-72% of the cis isomer. The results may be interpreted on the basis of a puckered ring and a preference for substituents to adopt a pseudoequatorial conformation. 

A study investigated the use of various bases, such as potassium hydroxide, potassium tert-butoxide, sodium methoxide, methyllithium, rrrf-butyllithium, sec-butyllithium, phenyllithium, lithium diisopropylamide, and lithium hcxamethyldisila/anidc over a temperature range of — 78 to 80°C in the dehydrofluorination of 2-(fluoromethoxy)-l,l,l,3,3,3-hexafluoropropane to give 2-(fluoromethoxy)pentafluoropropene.28... 

Shibasaki made several improvements in the asymmetric Michael addition reaction using the previously developed BINOL-based (R)-ALB, (R)-6, and (R)-LPB, (R)-7 [1]. The former is prepared from (R)-BINOL, diisobutylaluminum hydride, and butyllithium, while the latter is from (R)-BINOL, La(Oz -Pr)3, and potassium f-butoxide. Only 0.1 mol % of (R)-6 and 0.09 mol % of potassium f-butoxide were needed to catalyze the addition of dimethyl malonate to 2-cy-clohexenone on a kilogram scale in >99% ee, when 4-A molecular sieves were added [15,16]. (R)-6 in the presence of sodium f-butoxide catalyzes the asymmetric 1,4-addition of the Horner-Wadsworth-Emmons reagent [17]. (R)-7 catalyzes the addition of nitromethane to chalcone [18]. Feringa prepared another aluminum complex from BINOL and lithium aluminum hydride and used this in the addition of nitroacetate to methyl vinyl ketone [19]. Later, Shibasaki developed a linked lanthanum reagent (R,R)-8 for the same asymmetric addition, in which two BINOLs were connected at the 3-positions with a 2-oxapropylene... 

In the case of HWE reactions of phosphonate esters containing a charge-stabilizing electron-withdrawing group, for example, as in trimethyl phosphono-acetate, the carbanion is often generated by reaction with potassium fcrf-butoxide, sodium hydride, n-butyllithium or similar base. Direct reaction with an aldehyde or ketone then gives the ( )-a,P-unsaturated ester as the major product (see Protocol 6). The nature of the phosphonate (see Section 3), and the substitution of the aldehyde or ketone, can influence the stereochemical outcome of these reactions as can, to a lesser extent, the reaction temperature and solvent.16... 

Wrrno reaction, bases n-Butyllithium (see Potassium t-butoxide). Lithium ethoxide. Potassium t-butoxide. Sodium bistrimethylsilylamide. Sodium ethoxide (see Potassium t-butoxide). Sodium bydride-Dimethyl sulfoxide [see DMSO-derived reagent (a)]. Sodium methoxide. 

The base-induced monodehydrochlorination reaction was originally introduced as the second step of a convenient two-step synthesis of methylenecyclopropanes from alkenes. The first step involves carbene-type cyclopropanation of the alkene with a 1,1-dichloroalkane and either butyllithium or sodium bishexamethyldisilazanide as the base. The dehydrochlorination is then carried out by reacting the intermediate 1-alkyl-1-chlorocyclopropane with potassium tert-butoxide in dimethyl sulfoxide. For ordinary unhindered chlorocyclopropanes this procedure gives from about 60% to nearly quantitative yields of products (Table 1). The ready availability of the starting materials and reagents makes the base-induced dehydrochlorination a most useful 1,2-elimination reaction for preparation of methylenecyclopropanes. The procedure is illustrated by the synthesis of l,l-dimethyl-2-methylenecyclopropane (3) from 2-methylpropene ( ) ... 

Treatment of the phosphine resin 33 with alkyl bromides, e.g. 34, gave the corresponding phosphonium bromide 35 in excellent yields. The formation of the phosphorane was described as a cmdal step, for which the transport of the base to the phosphonium site within the polymer was essential. Various bases, such as sodium hydride, potassium tert-butoxide in THF, and n-butyllithium in dioxane, have been employed. Good results for the formation of the ylide were obtained with a mixture of sodium methoxide, methanol, and THF, and more recently with sodium bis(trimethyl)silylamide in THF [34, 35]. After the addition of aldehyde 36... 

Poly(e-mercapto acids). In a series of papers, Overberger and Weise (17, 20, 21) reported the polymerization of e-thiocaprolactone (XXIV) and of some substituted analogs (see Table VI). XXIV could be polymerized in bulk or tetrahydrofuran solution, using bases such as butyllithium, potassium ferf-butoxide, or sodium as initiators. A1C13 as initiator gave a crosslinked product. Linear poly(e-thiocaprolactone) is crystalline and soluble in chlorinated hydrocarbons. 

Mol (9.6 or 11.3 g) of powdered sodium or potassium f-butoxide and 50 ml of hexane or pentane are placed into the flask. The mixture is cooled to — 70 °C and a solution of 0.10 mol of butyllithium in 70 ml of hexane is added over a few seconds with efficient stirring. The suspension is then cooled to —40 °C and 0.10 mol of TMEDA is added in one portion. In the case of sodium terf-butoxide a homogeneous solution is formed, the addition of TMEDA to the BuLi-potassium teH-butoxide mixture results in a fine suspension. The mixtures are kept below — 30 °C since at 0 °C or higher the TMEDA is attacked by the base. 

Alkylation and acylation of dithiane oxides are highly stereoselective processes. In such transformations, it is noticed that the anti substrate leads to the syn acyldithiane oxide (Scheme 4.55), with the choice of base being pivotal in the process. The use of butyllithium for acylation and sodium t-butoxide/butyllithium mixtures for alkylation with aldehydes tends to give the cleanest and most efficient reactions. Of late, simple 2-substituted dithiane oxides have been prepared with very high enantioselectivity, and such compounds have become the preferred starting materials for the various systems under scrutiny. 

Some bases that are typically used to form the phosphonate ester carbanion include sodium hydride, potassium fert-butoxide, and butyllithium. The following reaction sequence is an... 

It is important to consider interactions between NHCs and alkali metals since, in many cases, NHCs are generated by deprotonation of a precursor molecule using an alkali salt of a strong base, such as potassium teri-butoxide, sodium hydride, potassium hydride, or u-butyllithium [19,20]. The influence of alkali metals in solution on stable diaminocarbenes has been investigated by C NMR and it has been postulated that metal ions in solution may act as catalysts for the dimerization of these NHCs [21]. Crystallographically characterized group 1 centers with coordinated neutral NHC ligands, however, are few and far between. 

The first example of a catalytic asymmetric Michael addition of a Horner-Wadsworth-Emmons reagent to enones was developed by the Shibasaki group using (J )-ALB ent-18 as the catalyst (Scheme 19.28). When sodium tert-butoxide was used as a base instead of butyllithium, the competitive 1,2-addition could be suppressed and the yield of 1,4-addition product increased. 

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