Lewis lithium

Other Organolithium Compounds. Organoddithium compounds have utiHty in anionic polymerization of butadiene and styrene. The lithium chain ends can then be converted to useflil functional groups, eg, carboxyl, hydroxyl, etc (139). Lewis bases are requHed for solubdity in hydrocarbon solvents. 

Many organic syntheses requHe the use of stericaHy hindered and less nucleophilic bases than //-butyUithium. Lithium diisopropylamide (LDA) and lithium hexamethyldisilazide (LHS) are often used (140—142). Both compounds are soluble in a wide variety of aprotic solvents. Presence of a Lewis base, most commonly tetrahydrofuran, is requHed for LDA solubdity in hydrocarbons. A 30% solution of LHS can be prepared in hexane. Although these compounds may be prepared by reaction of the amine with //-butyUithium in the approprite medium just prior to use, they are also available commercially in hydrocarbon or mixed hydrocarbon—THF solvents as 1.0—2.0 M solutions. 

Another synthesis of the cortisol side chain from a C17-keto-steroid is shown in Figure 20. Treatment of a C3-protected steroid 3,3-ethanedyidimercapto-androst-4-ene-ll,17-dione [112743-82-5] (144) with a tnhaloacetate, 2inc, and a Lewis acid produces (145). Addition of a phenol and potassium carbonate to (145) in refluxing butanone yields the aryl vinyl ether (146). Concomitant reduction of the C20-ester and the Cll-ketone of (146) with lithium aluminum hydride forms (147). Deprotection of the C3-thioketal, followed by treatment of (148) with y /(7-chlotopetben2oic acid, produces epoxide (149). Hydrolysis of (149) under acidic conditions yields cortisol (29) (181). 

Beecham P-lactamase iiihibitoi BRL 42715 [102209-75-6] (89, R = Na), C IlgN O SNa (105). Lithium diphenylamide, a weaker base, was used to generate the anion of (88) which on sequential treatment with l-methyl-l,2,3-ttia2ole-4-carbaldehyde and acetic anhydride gives a mixture of diastereomers of the bromoacetate (90). Reductive elimination then provided the (Z)-penem (89, R = d5 Q [ OC15 -p) as major product which on Lewis acid mediated deprotection gave BRL 42715 (89, R = Na). 

Cationic polymerization with Lewis acids yields resinous homopolymers containing cycHc stmctures and reduced unsaturation (58—60). Polymerization with triethyl aluminum and titanium tetrachloride gave a product thought to have a cycHc ladder stmcture (61). Anionic polymeriza tion with lithium metal initiators gave a low yield of a mbbery product. The material had good freeze resistance compared with conventional polychloroprene (62). 

Most other studies have indicated considerably more complex behavior. The rate data for reaction of 3-methyl-l-phenylbutanone with 5-butyllithium or n-butyllithium in cyclohexane can be fit to a mechanism involving product formation both through a complex of the ketone with alkyllithium aggregate and by reaction with dissociated alkyllithium. Evidence for the initial formation of a complex can be observed in the form of a shift in the carbonyl absorption band in the IR spectrum. Complex formation presumably involves a Lewis acid-Lewis base interaction between the carbonyl oxygen and lithium ions in the alkyllithium cluster. 

Resoles are usually those phenolics made under alkaline conditions with an excess of aldehyde. The name denotes a phenol alcohol, which is the dominant species in most resoles. The most common catalyst is sodium hydroxide, though lithium, potassium, magnesium, calcium, strontium, and barium hydroxides or oxides are also frequently used. Amine catalysis is also common. Occasionally, a Lewis acid salt, such as zinc acetate or tin chloride will be used to achieve some special property. Due to inclusion of excess aldehyde, resoles are capable of curing without addition of methylene donors. Although cure accelerators are available, it is common to cure resoles by application of heat alone. 

Examine the eleetrostatic potential map of eaeh nueleophile (enamine, silyl enol ether, lithium enolate and enol) with emphasis on the face of the nucleophilic alkene carbon. Rank the nucleophiles from most electron rich to least electron rich. What factors are responsible for this order (Hint For each molecule, consider an alternative Lewis structure to that given above that places a negative charge on the nucleophilic carbon.)... 

Shibasald et al. reported that lithium-containing, multifunctional, heterobimetallic catalysts such as LaLi3tris((l )-6,6 -dibromobinaphthoxide) 35, with moderate Lewis acidity in non-polar solvents, promote the asymmetric Diels-Alder reaction to give cycloadducts in high optical purity (86% ee) [53] (Scheme 1.67). The lithium... 

Quite a number of asymmetric thiol conjugate addition reactions are known [84], but previous examples of enantioselective thiol conjugate additions were based on the activation of thiol nucleophiles by use of chiral base catalysts such as amino alcohols [85], the lithium thiolate complex of amino bisether [86], and a lanthanide tris(binaphthoxide) [87]. No examples have been reported for the enantioselective thiol conjugate additions through the activation of acceptors by the aid of chiral Lewis acid catalysts. We therefore focussed on the potential of J ,J -DBFOX/ Ph aqua complex catalysts as highly tolerant chiral Lewis acid catalyst in thiol conjugate addition reactions. 

The synthesis of the right-wing sector, compound 4, commences with the prochiral diol 26 (see Scheme 4). The latter substance is known and can be conveniently prepared in two steps from diethyl malonate via C-allylation, followed by reduction of the two ethoxy-carbonyl functions. Exposure of 26 to benzaldehyde and a catalytic amount of camphorsulfonic acid (CSA) under dehydrating conditions accomplishes the simultaneous protection of both hydroxyl groups in the form of a benzylidene acetal (see intermediate 32, Scheme 4). Interestingly, when benzylidene acetal 32 is treated with lithium aluminum hydride and aluminum trichloride (1 4) in ether at 25 °C, a Lewis acid induced reduction takes place to give... 

Lithium hexafluorophosphate is thermally unstable in the solid state [52], where it decomposes at about 30 °C [53], In solvents and solvates it is more stable. Decomposition begins in the range from 80 °C [53] to about 130 °C [13], yielding scarcely soluble LiF and the Lewis acid PF5 which in turn initiates polymerization of cyclic... 

Lithium tetrafluoroborate yields only poorly conducting solutions with all solvents. It is unstable [61] and also leads to polymerization with cyclic ethers initiated by the corresponding Lewis base BFj. 

As far as investigated77, most reactions of the allyllithium-sparteine complexes with electrophiles proceed antarafacially, either as SE2 or anti-SE2 reactions. As a working hypothesis it is assumed that the bulky ligand obliterates the Lewis acid properties of the lithium cation. 

Table 10 shows examples of. vvn-sclcctive enolate condensations with imines using different types of enolates. All enolates used in these experiments were prepared based on the corresponding lithium enolate by treatment with different Lewis acids, where the lithium enolates themselves were generated with lithium diisopropylamide (LDA) at — 78 °C. 

As an alternative to lithium enolates. silyl enolates or ketene acetals may be used in a complementary route to pentanedioates. The reaction requires Lewis acid catalysis, for example aluminum trifluoromethanesulfonate (modest diastereoselectivity with unsaturated esters)72 74 antimony(V) chloride/tin(II) trifluoromethanesulfonate (predominant formation of anti-adducts with the more reactive a,/5-unsaturated thioesters)75 montmorillonite clay (modest to good yields but poor diastereoselectivity with unsaturated esters)76 or high pressure77. 

In 1957, Bamford et reported that the addition of small amounts of lithium chloride brought about a significant (up to two-fold) enhancement in the rate of polymerization of AN in DMF and led to a higher molecular weight polymer. Subsequent studies have shown this to be a more general phenomenon for polymerizations involving, in particular, acrylic and vinyl heteroaromatic monomers in the presence of a variety of Lewis acids.71... 

Lewis acids, 15,72,106,108-11,112,116,128 Lithiation, 84 reductive, 68 o-Lithiation, 40 a-Lithiosilanes, 65, 68 o-Lithiosilyl enol ethers, 77 a-Lithiovinylsilanes, 69 Lithium bis(phenyldimethylsilyl)cuprate, 8,53... 

The zinc chloride is acting here as a Lewis acid. Similarly, thiirane dioxides react with metal halides such as lithium and magnesium chlorides, bromides and iodides in ether or THF to give the halo-metal sulfmates (130) in fair yields157. 

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