Bases Potassium r-butoxide

Formation of the excited amide anion of coelenteramide as the light emitter in the luminescence reaction of coelenterazine was experimentally supported by the experiment of Hori et al. (1973a), in which 2-methyl analogue of coelenterazine was used as the model compound. The summary of their work is as follows In the presence of oxygen, la and lb in DMF emitted bright blue luminescence (Amax 480 and 470 nm, respectively), and produced the reaction products Ha and lib, respectively. The fluorescence emission of lib (Amax 470 nm) and that of the spent chemiluminescence reaction of lb, both in DMF plus a base (potassium r-butoxide), were identical to the chemiluminescence emission of lb in DMF. The fluorescence emission of Ha... 

Luche to improve the yield. When the intermediate epoxy hydrazone is isolable, addition of a strong base, potassium r-butoxide or potassium diisopropylamide (KDA), improves the yield. Triethylamine is the base of choice in the case of an unstable epoxy hydrazone (equation I). 

With the poor base potassium benzoate only 7.2% Hofmann product (22) could be obtained with the strong base potassium r-butoxide the yield is raised to 20%. ... 

Wadsworth—Homer—Emmons olefination of aldehyde 464 with glycine phosphonate 571 affords dehydroamino acid 572. The stereochemical outcome of the reaction hinges on the base used for deprotonation. A lithium base such as LDA gives a 1.5 1 mixture of (Z)-572 and the corresponding E isomer (88% yield), whereas a potassium base (potassium r -butoxide) produces only the Z-isomer, in 77% yield [180]. 

The ratio of products 15 and 16 is dependent on the structures, base, and the solvent. The kinetics of the reaction is likewise dependant on the structures and conditions of the reaction. Thus addition or cyclization can be the rate-determining step. In a particularly noteworthy study by Zimmerman and Ahramjian, it was reported that when both diastereomers of 20 were treated individually with potassium r-butoxide only as-epoxy propionate 21 was isolated. It is postulated that the cyclization is the rate-limiting step. Thus, for these substrates, the retro-aldolization/aldolization step reversible. ... 

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. 

The first investigations in the 1960s [11,12] established the base-induced isomerization of alkyne precursors as the most practical and general route for the synthesis of alkoxy-and aryloxyallenes. In the meantime, a number of monosubstituted allenes 8 bearing an achiral or a chiral group R is smoothly accessible by this efficient procedure (Scheme 8.5) [1, 2,13-19]. Beside the most commonly used base potassium tert-butoxide, other bases, e.g. n-butyllithium, are also applicable for this isomerization. Recently, the yields of alkyne-allene isomerizations could be significantly increased, in particular with aryloxy-substituted allenes, by using microwave irradiation (Eq. 8.1) [20]. 

That the base strength is decisive has also been shown by Becker.8 The replacement of potassium r-butoxide in the reaction of phenyl />-tolyl sulfone with benzalaniline by sodium methoxide resulted in the isolation of the addition product 7. This reaction is possible because the... 

In the case of methyl-substituted 2-phenylbenzo[b]furans, the methyl groups show differing reactivity depending on the site to which they are attached. Thus, reaction of 2-(/ -tolyl)-5-methylbenzo[b]furan (34) with Schiff s base from benzaldehyde and p-chloroaniline in the presence of potassium hydroxide yields 2-(stilben-4-yl)-5-methylbenzo[bjfuran (35), whereas with potassium r-butoxide the 5-methyl group of the benzofuran ring also reacts, yielding the 5-styryl derivative 36.26,27... 

Alkylation of phenyl sulfones.1 A convergent synthesis in which two synthons become attached through a double bond depends on the a-alkylation of the anion of a phenyl sulfone followed by a / -elimination. The synthesis of retinoic acid (4) is typical of the process. Potassium r-butoxide is used as base the recommended solvent is THF/NMP = 50 10. 

Wittig reactions. Dehmlow and Barahona-Naranjo2 have examined use of phase-transfer catalysts in addition to a base in Wittig reactions and conclude that best results are obtained with solid potassium r-butoxide in benzene without an extra catalyst. Solid NaOH is superior to aqueous NaOH. KF and K2C03 are not generally useful. 

Crounse and Desai29 showed further that 2-(/>-tolyl)benzo[6]furan with Schiff s base derived from terephthalaldehydic acid and aniline gives, on treatment with excess potassium r-butoxide, the corresponding stilbene carboxylic acid. Schiff s base derived from phthalaldehydic acid and aniline exists30 as the 3-anilinophthalide (40). Nevertheless, this also reacts similarly with, for example, the naphthofuran (39) to form 2-(2 -carboxystilben-4-yl)naphtho [ 1,2-6]furan (41).29 Analogous car-... 

Careful treatment of 1,3-disubstituted imidazolium salts (e.g., 350) with sodium hydride (in some cases addition of a small amount of potassium /< r/-butoxide is also recommended) in tetrahydrofuran gives stable carbenes of type 351 (see also Section 2.4.4.2.3). They behave as rather strong bases (p , 24 in DMSO) and nucleophiles. Thus, carbene 351 and salt 350 form a crystalline bis(carbene)proton complex 352 which is a rare example of an asymmetrical hydrogen bridge between two carbon centers. By the action of BF3, B2H6 or AlH3NMe3 stable mesoionic adducts of type 353 are obtained. 

Cross-conjugated dienamines may also be obtained by base-catalysed isomerization of propargylic amines with potassium r-butoxide in dimethyl sulphoxide547. 

The primary product is the a-hydroperoxy ketone. The corresponding alcohol is obtained after reductive work-up. Initially this was achieved using zinc dust in acetic acid, e.g. (22) to (23). Potassium r-butoxide was used to generate the enolate in this case and indeed is frequently the preferred base (vide infra). Subsequently it was found that the presence of triethyl phosphite in the reaction mixture pro-... 

Cleavage af nucleosides. Purine and pyrimidine bases can be cleaved from derivatives of adenosine, cytidine, and uridine by potassium r-butoxide in dioxane. 

Condensation of an a, -unsaturated ketone with benzylamine gives the corresponding Schiff base. Treatment with a base such as potassium r-butoxide affects rearrangement to a benzaldehyde derivative, as shown in Scheme 82. Hydrolysis of the latter with dilute acetic acid furnishes the corresponding saturated ketone with concomitant formation of benzaldehyde. 

The formation of methylenecyclopropene was surmised from experiments where 1,2-dihalo-1-methylcyclopropanes are treated with base . Thus the reaction of 99 with potassium r-butoxide yielded r-butoxymethylenecyclopropane 100. When meth-anethiol is added to the reaction mixture, 101 is isolated (equation 80). These results can be rationalized in terms of methylenecyclopropene as a reactive intermediate. 

Bromination of an olefin and double dehydrobromination of the resulting 1,2-dibromide is a classical method for the generation of 1,3-dienes (Table 1). Bromination of a double bond can be done with molecular bromine or, more conveniently, with pyridinium bromide perbromide . A variety of bases has been employed for dehydrobromination. While potassium hydroxide and sodium methoxide have been used for a long time, lithium carbonate-lithium chloride in DMF or hexamethylphosphoric triamide (HMPA) works well in many cases . Double dehydrobromination with hindered bases such as potassium r-butoxide or diazabicyclononene (DBN) and diazabicycloundecene (DBU) give good results. 

Sternbach and coworkers pointed out that the reactions of the 6-chloro-2-chloromethyl-l,2-dihydro-4-phenylquinazoline 3-oxides 11 with a base gives either the 1,3-dihydro-2//-azirino[ 1,2-fl]quinazoline 4-oxides 13 or the 3H-1,4-benzodiazepine 4-oxide 15. In the first step of the reaction the anion 12 is formed by abstraction of a proton from the 1-nitrogen. The intermediate anion 12 can rearrange to the ring-chain tautomer 14. The relative stabilities of the two anions 12 and 14 are assumed to determine whether product 13 or 15 is formed. Thus when R is hydrogen or chloromethyl, the anion 12 is relatively sufficiently stable to allow the formation of the azirino-quinazoline 13. If, however, R is the electron-releasing methyl group, the anion 12 is destabilized and is converted to anion 14, which leads to benzodiazepine 15. The solvent polarity also influences the stability of the anions 12 and 14. In a nonpolar solvent (ether), the 5//-benzodiazepine 16 (R = Me) was obtained, which can be derived from anion 12 (R = Me) via the azirinoquinazoline 13 (R = Me). In a polar solvent (aqueous ethanol), however, the 3H-benzodiazepine 15 derived from anion 14 (R = Me) was the major product. As bases, potassium /er/-butoxide and sodium hydride were used. ... 

If the anions of these acids are good leaving groups, elimination from their enol esters can be effected by the bases used for elimination of hydrogen halides. Enol triflates, on treatment with pyridine (Scheme 46), 2,6-di-r-butyl phenoxide (Scheme 47) or potassium r-butoxide (Scheme 48) yield the corresponding alkynes. 

N-Alkylation. Exclusive N-alkylation of pyrrole, pyrazole, and related hetero-cyclcs is possible with potassium r-butoxide as base and 18-crown-6 as catalyst in ether or benzene. 

Studies by Feuer of the nitration of cyclic ketones with amyl nitrate have shown potassium r-butoxide to be the best base and tetrahydrofurane the best solvent. Under these conditions dipotassium 2,5-dinitrocyclopentanone is obtained in good... 

Bases, strong Choline. Claisen s alkali. Lithium (potassium, sodium) amide (ethoxide, hydroxide, methoxide). Lithium nitride. Phenyllithium (potassium, sodium). Potassium r-butoxide. Potassium (sodium) 2-methyl-2-butoxide. Resins Amberlite IRA-dOO. Dowex... 

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