Alkoxides as bases

Conversion of PGA2 to the highly sensitive PGC2 was accomplished by deconjugation of the enone system by formation of the y-extended enolate using rm-alkoxide as base and a-protonation by pH 4 buffer. 

The carbanionic species thus formed is protonated to give the final product 3. The use of an alkoxide as base leads to formation of a carboxylic ester as rearrangement product use of a hydroxide will lead to formation of a carboxylic acid salt ... 

The classical Michael reaction is carried out in a protic organic solvent—e.g. an alcohol—by use of an alkoxide as base—e.g. potassium r-butoxide or sodium ethoxide. 

Nielsen and Bedford synthesized gem-dinitroalkanes (147) from the Michael addition of organolithium reagents to a-nitroalkenes (146) followed by quenching of the resulting nitronate anion with tetranitromethane. The same reaction using alkoxides as bases provides P-alkoxy-gem-dinitroalkanes (148). ... 

Alkylation of enolate is an important synthetic method.27 The alkylation of relatively acidic compounds such as /i-dikctoncs, /i-ketoesters, and esters of malonic acid can be carried out in alcohols as solvents using metal alkoxides as bases. The presence of two electron-withdrawing substituents facilitates formation of the enolate resulting from removal of a proton from the carbon situated between them. Alkylation then occurs by an Sn2 process. Some examples of alkylation reactions involving relatively acidic carbon acids are shown in Scheme 1.5. These reactions are all mechanistically similar in that a... 

Darzens reaction. Under the usual condiiions (sodium alkoxides as base and the corresponding alcohol as solvent), the condensation of aliphatic aldehydes with a-halo... 

Acylation at a methyl group in an unsymmetrical ketone, e.g. 15 usually occurs regioselectively even with traditional methods (ester as acylating agent, corresponding alkoxide as base). We shall return to this subject in chapter 10 with other specific enol equivalents, but you can see already that virtually any 1,3-diketone can be made by one of these methods. 

Potassium Alkoxides. The most widely used potassium bases are potassium tert-hu. oAde [865-47-4] (KTB) and potassium / i -amylate [41233-93-6] (KTA). These strong alkoxide bases offer such advantages as base strength (pX = 18), solubiUty (Table 5), regio/stereoselectivity because of bulky alkyl groups, and stabiUty because of the lack of a-protons. On storage, KTB and KTA have long shelf Hves under inert atmosphere (see... 

Alkoxides, RO, have dual reactivity, and can act as bases or nucleophiles. 

The most common conditions employed in the Madelung process are sodium/potassium alkoxide or sodium amide at elevated temperature (200-400 C). The Madelung reaction could be effected at lower temperature when -BuLi or LDA are employed as bases/ The useful scope of the synthesis is, therefore, limited to molecules which can survive strongly basic conditions. The process has been successfully applied to indoles bearing alkyl substituents. ... 

The Friedlander reaction originally was performed in ethanolic alkoxide. Amine bases, such as piperidine, have been used. Anion exchange resins have also been used. ... 

The a -halosulfone, required for the Ramberg-Backlund reaction, can for example be prepared from a sulfide by reaction with thionyl chloride (or with N-chlorosuccinimide) to give an a-chlorosulfide, followed by oxidation to the sulfone—e.g. using m-chloroperbenzoic acid. As base for the Ramberg-Backlund reaction have been used alkoxides—e.g. potassium t-butoxide in an etheral solvent, as well as aqueous alkali hydroxide. In the latter case the use of a phase-transfer catalyst may be of advantage. ... 

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. 

A previous method [1] of preparing 3,3-dimethylbutyne by dehydrochlorination of the title compound in a sodium hydroxide melt is difficult to control and hazardous on the large scale. Use of potassium ferf-butoxide as base in DMSO is a high-yielding, safe and convenient alternative method of preparation of the alkyne [2], See Dimethyl sulfoxide Metal alkoxides See other HALOALKANES... 

Many acylation reactions of esters using sodium hydride as base appear auto-catalytic, with considerable potential for runaway, since the active base in solution is an alkoxide and the alcohol is a product of reaction [4], A safe form of sodium hydride (as a solid solution in a halide) for large-scale industrial use has been claimed [3],... 

Sodium and potassium alkoxides are often used as bases in organic synthesis. 

OH ratio on the rate of crystallization and crystallite size investigated Prehydrolysis method. Synthesis using binary mixtures of tetrabutylphosphonium hydroxide and tetraethylphosphonium hydroxide instead of TPAOH as base and template TEOS and TBOT are sources of Si and Ti, respectively. Molar gel composition, SiO2 xTiO2 0.4 ( TEPOH + (1 — jd)TBPOH) 30H2O (x = 0-0.02) temperature = 443 K and synthesis time = 4 days Influence of nature of silicon and titanium alkoxides on the incorporation of Ti Wetness impregnation method... 

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