Lithium Lewis acid

The Lewis-acid lithium strives to bind the Lewis-base fluorine. 

Noyori et al. proposed that the reaction would be initiated by complexation of the Lewis acidic lithium cation to the ketone oxygen atom then hydride transfer occurs from aluminum to the carbonyl carbon by way of a six-membered chairlike transition state3 (Scheme 4.3c). Between the two competing six-membered chairlike transition states A and B, transition state B is disfavored, due to the substantial n/it-type electronic repulsion between the axially oriented binaph-thoxyl oxygen and the unsaturated phenyl or alkenyl moiety. Although there is a 1,3-diaxial steric interaction between the Al-0 and C-R bonds in transition state... 

An additional procedure leading from a titanate (1) (X = Y = i-PrO) to the corresponding dichloride (X = Y = Cl) is to treat the former with Tetrachlorosilane and pump off (i-PrO)2SiCl2. A method in which the Ti-TADDOLate is present together with another Lewis acid Lithium Chloride) is to treat a TADDOL (2) with 2 equiv n-Butyllithium, followed by TiCU. ... 

When the content of CajfPO ) in the NCPE is increased to 20% the ionic conductivity of the NCPE decreases. This decrease in the ionic conductivity can also be attributed to the change in the crystallinity of PEO in the nanocomposite polymer electrolytes (Capuglia et al., 1999). According to Scrosati and co-workers (Scrosati et al., 2001), the Lewis acid groups of the added inert filler may compete with the Lewis acid lithium cations for the formation of complexes with the PEO chains as well as the anions of the added lithium salt. In the present study, the filler nano CajfPO lj, which has a basic center can react with the Lewis acid centers of the polymer chain and these interactions lead to the reduction in the crystallinity of the polymer host. Nevertheless, the result provides LL conducting pathways at the filler surface and enhances ioiuc transport. 

Ring-opening Reactions. In combination with a Lewis acid, lithium TIPS-acetylide reacts effectively with epoxides to form the desired adducts (eq 34). ... 

Another advance in this field is the catalytic enantioselective a-fiuorination of acid chlorides (eq 28). Here, NFSi is an effective electrophilic fiuorination reagent in the presence of a trifunctional catalytic system. This is a practical method that produces a-fluorocarboxylic acid derivatives. A third catalyst, a Lewis acidic lithium salt, could be introduced to amplify yields of aliphatic products, primarily through activation of the NFSi. 

One can anticipate that the Lewis acid groups on the surface of the ceramics (e.g. the -OH groups on the Si02 surface) may compete with the Lewis-acid lithium cations for the attentions of the PEO chains, as well as with the anions of the LiX salt (see Figure 1.8). 

Weak Lewis Acid. Lithium chloride is a weak Lewis acid that forms mixed aggregates with lithium dialkylamides, enolates, alkoxides, peptides, and related hard Lewis bases. Thus LiCl often has a dramatic effect on reactions involving these species. In the deprotonation of 3-pentanone by Lithium 2,2,6,6-... 

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. 

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... 

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