Lithium 2- ethoxide, anionic

Parts A and B of the procedure correspond to preparation of lithium tetramethylpiperidide, and its use in the in situ preparation and addition of dibromomethyllithium to the ester 1 producing tetrahedral intermediate 2. In Part C a mixture of lithium hexamethyldisilazide and lithium ethoxide is prepared for addition in Part D to the solution of 2. The silazide base serves to deprotonate the mono and dibromo ketones that are formed on initial warming of the reaction to -20°C, thus protecting them as the enolate anions 4 and 3. Addition of the sec-butyllithium in Part... 

The X-ray structure of 23, shown in Figure 9, confirms that the hydrogen-bonding pattern and the internal geometry of the anion is similar to that reported for lithium phenylnitronate by Boche and coworkras . The lithium phenylnitronate, prepared from phenylnitromethane and lithium ethoxide in ethanol, exhibits the presence of hydrogen bonds with ethanol incorporated into the crystal. In turn, this agrees with the conclusions derived for nitronates Ifom acidity measuranents on nitro compounds in protic solvents (Figure 10). 

The reactivity of 2-alkyloxazoles in base-catalyzed additions and condensations is due to the intermediacy of delocalized anions analogous to (142). 2-Methyl-4,5-diphenyloxazole forms the adduct (278) by the action of benzophenone in liquid ammonia containing lithium amide (equation 89), and 2-methylbenzoxazole condenses with diethyl oxalate in the presence of potassium ethoxide to yield the keto ester (279). Anions with more extended conjugation are involved in the condensation of 2-(propen-l-yl)benzoxazole with diethyl oxalate (equation 90) and in the formation of the stilbene derivative (280) from 5-phenyl-2-p-tolyloxazole and benzylideneaniline (78AHC(23)l7l). 

Additions of the Michael type of nucleophiles to the carbon-carbon double bond of thiete 1,1-dioxides to give 3-substituted thietane 1,1-dioxides occur readily. The addition of hydrogen has been discussed in Section A. Nucleophiles include cyanide, the anion of nitroethane, the lithium salt of r-butyl o-tolyl sulfone, dimethylamine, cyclohexylamine, ethoxide, and hydrogen sulfide. The reaction is exemplified by the synthesis of 278. Additions to 3-chloro-2H-thiete 1,1-dioxide most likely proceed by an addition-elimination mechanism an example is shown for the addition of the anion of dimethylmalonate to give 279. The replacement of a 3-morpholinyl group by a 3-A methyl-A-phenylamino group in thiete 1,1-dioxide is another example of addition-elimination. An addition of ethoxide with elimination of p-nitrophenyl anion may occur with 268 (Ar = / -N02C6H4). " Addition of bromine via N-bromo-succinimide to the double bond of 4-phenyl-2H-thiete 1,1-dioxide occurs only in 1.5% yield. ... 

Procedures which utilize selenides are similar, but a-lithio selenides are not generally preparable via simple deprotonation chemistry, due to facile selenium-lithium exchange. - Selenium-stabilized anions are available, however, by transmetalladon reactions of selenium acetals and add readily to carbonyl compounds. The use of branched selenium-stabilized anions has been shown to result exclusively in 1,2-addidon to unhindered cyclohexenones, in contrast to the analogous sulfur ylides. The resulting 3-hydroxy selenides undergo elimination by treatment with base after activation by alkylation or oxidation (Scheme 10). An alternative method of activating either p-hydroxy selenides or sulfides toward elimination involves treatment of a chloroform solution of the adduct with thallium ethoxide (Scheme 11). A mechanism involving the intermediacy of a selenium ylide is proposed. 

Attempts were made to prepare a terminal 5,6-epiminofuranose derivative by treatment of 6-benzamido-6-deoxy-l,2-(9-isopropylidene-5-(9-methanesulfonyl-ot-D-glucofuranose with lithium aluminum hydride or sodium ethoxide. In both cases, only 6-benzamido-6-deoxy-l,2-(9-isopropylidene-ot-D-glucofuranose was obtained, indicating hydrolysis of the methanesulfonate. b. A-Aryl(alkyl)sulfonylamines.—In comparison with the preceeding method, eyelization of vicinal sulfonamido-sulfonates has two advantages formation of oxazolines is excluded, and the reaction proceeds more readily because of enhanced acidity of the N-H group and facile formation of the N anion, which is considered the reactive species. Lower temperatures and weaker bases are therefore sufficient to induce eyelization. 

S93> The lithium anion adds to N-tosylimines to generate 3-(benzotriazolylmethyl)propargylsulfonamides. In hot ethanolic sodium ethoxide these undergo cyclocondensation to the 2-arylpyrroles. The cyclization evidently occurs via allenic isomers formed under the basic conditions. The synthesis can also be adapted to... 

Diphenylmethylcarbanions. The carbanions based on diphenyl-methane (pZ a = 32) (see Table 1) are useful initiators for vinyl and heterocyclic monomers, especially alkyl methacrylates at low temperatures (46). 1,1-Diphenylalkyllithiums can also efficiently initiate the polymerization of styrene and diene monomers that form less stable carbanions. Diphenylmethyl-lithium can be prepared by the metalation reaction of diphenylmethane with butyllithium or by the addition of butyffithium to 1,1-diphenylethylene, as shown in equation 17. This reaction can also be utihzed to prepare ftinctionalized initiators by reacting butyffithium with a substituted 1,1-diphenylethylene derivative. Addition of lithium salts such as hthium chloride, lithium f-butoxide, or lithium 2-(2-methoxyethoxy)ethoxide with 1,1-diphenylmethylcarbanions and other organolithium initiators has been shown to narrow the molecular weight distribution and to improve the stabffity of active centers for anionic polymerization of both alkyl methacrylates and t-butyl acrylate (47,48). 

A dramatic development in the anionic polymerization of acrylate and methacrylate monomers was the discovery that by addition of lithium chloride it was possible to effect the controlled polymerization of f-butyl acrylate (86). Thus, using oligomeric (o -methylstyryl)lithium as initiator in THF at —78°C, the molecular weight distribution (M /Mn) of the polymer was 3.61 in the absence of lithium chloride but 1.2 in the presence of lithium chloride ([LiCl]/[RLi] = 5). In the presence of 10 equiv of LiCl, f-butyl acrylate was polymerized with 100% conversion and 95% initiator efficiency to provide a polymer with a quite narrow molecular weight distribution (My,/Mn = 1.05). More controlled anionic polymerizations of alkyl methacrylates are also obtained in the presence of lithium chloride. Other additives, which promote controlled pol5unerization of acylates and methacrylates, include lithium f-butoxide, lithium (2-methoxy)ethoxide, and crown ethers (47,48). The addition of lithium chloride also promotes the controlled anionic polymerization of 2-vinylpyridine. 

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