F-butoxide, as base

N-Alkylation. Exclusive N-alkvIation of pyrrole, pyrazole, and related hetero-liyclcs is possible with potassium f-butoxide as base and 18-crown-6 as catalyst in Other or bcn/cne. 

In an unusual ketone homologation, attempted Wittig reaction of methyltriphenyl-phosphonium bromide with 2- (or 4-) methoxy-4 -nitrobenzophenone (134) using potassium f-butoxide as base unexpectedly yielded methyleneketones with the exclusion of triphenylphosphine. ... 

The use of potassium f-butoxide as the base directly produced a low yield of 1-azirine contaminated with propiophenone. However, Nair has reported that azirine (37) can be prepared from hydrazone (34) in 63% yield by using the dimethylsulfinyl carbanion as the base.18... 

Subsequent alkylation of 21a-c with iodomethane and potassium f-butoxide as a base in THF affords 22a-c as the potassium complexes in 81-95% yield. Use of rubidium f-butoxide24 under the same conditions gives the corresponding rubidium complexes. Alkylation of 21a with iodoethane gives 22d... 

When phenolic nucleophiles were used, either potassium hydroxide or potassium f-butoxide was generally chosen as the base. When aliphatic hydroxyls constituted the nucleophiles, a stronger base was required and sodium hydride was generally chosen. 

This procedure has been patterned after the method by which the carbethoxy group is introduced into a few alicyclic ketones 6 and several cyclic ketones. Cyclohexanone has been reported to yield 50% of 2-carbethoxycyclohexanone when treated with sodium hydride and diethyl carbonate using ether as the solvent.7 The preparation of 2-carbethoxycycloheptanone using potassium f-butoxide and diethyl carbonate in benzene has been reported in 40% yield.8 Jacob and Dev report an 80% yield of the latter compound using sodium hydride as the base.9... 

Significantly, (a) a-sulfonyl carbanions of thiirane dioxides, generated from the latter in the presence of strong bases such as potassium f-butoxide and alkoxide ions , do epimerize to relieve steric repulsion between substituents as in 42 above and (b) the a-hydrogen in aryl-substituted three-membered sulfoxides (e.g. 46c) are sufficiently acidic to... 

Cyclic ketene acetals, which have utility as co-polymers with functional groups capable of cross-linking, etc., have been prepared by the elimination of HX from 2-halomethyl-l,3-dioxolanes. Milder conditions are used under phase-transfer conditions, compared with traditional procedures, which require a strong base and high temperatures. Solid liquid elimination reactions frequently use potassium f-butoxide [27], but acceptable yields have been achieved with potassium hydroxide and without loss of any chiral centres. The added dimension of sonication reduces reaction times and improves the yields [28, 29]. Microwave irradiation has also been used in the synthesis of methyleneacetals and dithioacetals [30] and yields are superior to those obtained with sonofication. 

Stevani and coworkers prepared and characterized a peracid intermediate, 4-chloro-pheny 1-0,0-hydrogen monoperoxalate (57) and found that no chemiluminescence was observed in the presence of activators (i.e. rubrene, perylene and DPA) and the absence of a base. Based on this result, the authors excluded 57 and similar peracid derivatives as HEI in the peroxyoxalate system. Moreover, 57 only emits light in the presence of an activator and a base with pK > 6, suggesting that a slow chemical transformation must still occur prior to the chemiexcitation step. Kinetic experiments with 57, using mainly imidazole, but also in the presence of other bases such as potassium 4-chlorophenolate, f-butoxide and l,8-bis(dimethylamino)naphthalene , showed that imidazole can act competitively as base and nucleophilic catalyst (Scheme 41). At low imidazole concentrations, base catalysis is the main pathway (steps 1 and 2) however, increasing the base concentration causes nucleophilic attack of imidazole catalyzed by imidazole to become the main pathway (steps la and 2a). Contrary to the proposal of Hohman and coworkers , the... 

When the reaction is run with potassium f-butoxide in THF at — 5°C, one obtains (after hydrolysis) the normal Knoevenagel product 45, except that the isocyano group has been hydrated (6-65).592 With the same base but with 1,2-dimethoxyethane (DME) as solvent the product is the nitrile 46.593 When the ketone is treated with 44 and thallium(I) ethoxide in a 4 1 mixture of absolute ethanol and DME at room temperature, the product is a 4-ethoxy-2-oxazoline 47.S94 Since 46 can be hydrolyzedS95 to a carboxylic acid592 and 47 to an a-hydroxy aldehyde,594 this versatile reaction provides a means for achieving the conversion of RCOR to RCHR COOH, RCHR CN, or RCR (OH)CHO. The conversions to RCHR COOH and to RCHR CN596 have also been carried out with certain aldehydes (R = H). 

The Oppenauer oxidation. When a ketone in the presence of base is used as the oxidizing agent (it is reduced to a secondary alcohol), the reaction is known as the Oppenauer oxidation,95 This is the reverse of the Meerwein-Pondorf-Verley reaction (6-25), and the mechanism is also the reverse. The ketones most commonly used are acetone, butanone, and cyclohexanone. The most common base is aluminum f-butoxide. The chief advantage of the method is its high selectivity. Although the method is most often used for the preparation of ketones, it has also been used for aldehydes. 

Furthermore, potassium hydroxide, which is virtually insoluble in DMF, acts as a far superior base than does sodium methoxide, being almost as effective as potassium f-butoxide. Hence, it has been suggested11,12 that the effective base is a complex derived from DMF and Schiff s base with potassium hydroxide, which then is soluble. 

A significant drawback of the standard conditions for palladium-catalyzed animation of aryl halides is the use of strong base. This procedure precludes the use of substrates with aromatic nitro groups, many substrates with enolizable hydrogens, substrates with esters other than /-butylesters, and substrates with base-sensitive stereochemistry, such as some protected amino acids. Thus, conditions that employ milder bases are required. A solution that involves reaction temperatures as low as those for reactions employing sodium f-butoxide has not been developed. However, carbonate and phosphate bases can be used with certain catalysts at reaction temperatures comparable to those of reactions involving the first- and second-generation catalysts. 

We have already mentioned the bulky f-butoxide—ideal for promoting E2 as it s both bulky and a strong base (p aH - 18). Here it is at work converting a dibromide to a diene with two successive E2 eliminations. Since dibromides can be made from alkenes (you will see how in the next chapter), this is a useful two-step conversion of an alkene to a diene, synthesis of a diene by a double E2 elimination... 

The rr-systems of the A2- and A3-piperideines are not reactive toward nucleophilic reagents. The A3-piperideine contains an isolated double bond whereas the A2-piperideine contains the electron-rich enamine functional group. However, treatment of either piperideine (10) or (11) with strong base (potassium f-butoxide) apparently does generate a small equilibrium concentration of the anion (217), as is evidenced by the equilibration of the A3-piperideine (10) to the more stable A2-isomer (11) (78T3027). The A2-piperideine is favored to such an extent that this reaction can be used preparatively (80JOC1336). 

Wittig-Homer reaction.2 The reagent reacts with a wide range of aldehydes, aliphatic, aromatic, and a,P-unsaturated, in the presence of a base to form (E)-a-methyl-a,p-unsaturated esters stereoselectively. The reaction can be carried out either with potassium f-butoxide in DMF or with K2C03 in C6H6/H20 and Aliquat 336 as phase-transfer agent. 

Z)-OL, -Unsaturated esters,l Wittig-Homer reactions generally show a preference for formation of (E)-alkenes. Thus (E)-a,p-unsaturated esters are obtained preferentially on reaction of aldehydes with trimethyl phosphonoacetate under usual conditions (potassium f-butoxide). Use of a highly dissociated base can favor (Z)-selectivity. The most effective base for this purpose is potassium hexamethyldisilazide, KN[Si(CH3)3]2, in combination with 18-crown-6, although even potassium carbonate with the crown ether is fairly effective. The (Z)-selectivity can be further enhanced by use of 1 as the phos-phonoester. Under these conditions, (Z)-unsaturated esters can be prepared from aliphatic and aromatic aldehydes with Z/E ratios as high as 50 1. The method is also useful for transformation of unsaturated aldehydes to (E,Z)-dienoates and (E,E,Z)-trienoates. 

Dehydrohalogenatioiu Alkyl halides can be converted into alkenes by solid potassium 1-butoxide and a catalytic amount of 18-crown-6. Petroleum ether with a suitable boiling point range is used as solvent. No reaction is observed in the absence of a crown ether other bases (KOH, K2CO3) are ineffective. The method is particularly useful for dehydrohalogenation of primary alkyl halides, which are converted into ethers by potassium f-butoxide under usual conditions. ... 

Preliminary experiments with a velated A/B component established that the coupling reaction could not be acc omplished directly with base or with a mild coordinating metal ion such as Zn(II or Ni(Il). However, the coupling was achieved by conversion of the ion of 2 into 3 t y the (DBU>2-adduct of Pd(OAc)2 followed by treatment of 4 with equimolar amo mts of DBU and excess 3. Palladium(II) was removed from the resulting 5 (40 )t= yield) by KCN. Potassium f-butoxide in the presence of Zn(Il) then cyclized th e free seco-ligand to the Zn complex 6. Acid treatment removed Zn(fl) and also t he r-butylcarbonyl group to afford 7. 

Hydroxylation of 1,3-diearbonyl compounds. Hydroxylation of 1 and 2 with oxygen in the presence of either NaH or potassium f-butoxide and triethyl phosphite in DMF affords the corresponding alcohols 3 and 4 in 50-70% yields. In the case of 1, an isomeric product (5) is obtained in 14% yield. When NaH is employed as base, a trace of H2O is required to initiate the reaction. 

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