Hydroxides as bases

Horhold et al. and Lenz et al. [94,95]. The polycondensation provides the cyano-PPVs as insoluble, intractable powders. Holmes et al. [96], and later on Rikken et al. [97], described a new family of soluble, well-characterized 2,5-dialkyl- and 2,5-dialkoxy-substituted poly(pflrfl-phenylene-cyanovinylene)s (74b) synthesized by Knoevenagel condensation-polymerization of the corresponding alkyl-or alkoxy-substituted aromatic monomers. Careful control of the reaction conditions (tetra-n-butyl ammonium hydroxide as base) is required to avoid Michael-type addition. 

The solution is prepared by dissolving 22.3 g (105 mmol) of potassium phosphate (Nakarai Chemicals, Japan) in water and adjusting the final volume to 35 mL. The original method5 used sodium hydroxide as base potassium phosphate is desirable for the extension of the present procedure to base-sensitive compounds. Under such conditions, the reaction with 9-(10-carbomethoxydecanyl)-9-BBN proceeds similarly without saponification of the ester group. 

In the early studies on luminol and related hydrazides the systems used were composed of either sodium or potassium hydroxide, as base, hydrogen peroxide as the oxidizing agent (more recently molecular oxygen, hypochlorite, iodide, and permanganate have also been used), and some type of initiator or activator. This initiator was frequently hypochlorite, persulfate, a transition metal... 

The Cannizzaro reaction under heterogeneous conditions (solid-liquid) using calcined barium hydroxide as base is greatly accelerated by low intensity ultrasound (cleaning... 

The Sonogashira reaction of 2-iodothiophene with 2-methyl-3-butyne-2-ol or trimethylsilylacetylene under phase transfer conditions using sodium hydroxide as base led to the formation of the expected products, which released their end group spontaneously under the applied conditions giving rise to the intermediate formation of 2-ethynylthiophene. This terminal acetylene, in turn, reacted with another molecule of aryl halide, yielding either non symmetrical or symmetrical diarylethynes. When 2-methyl-3-butyn-2-ol was used as acetylene equivalent68 it was possible to introduce a benzothiophene moiety in the second step, while the reaction of 2-iodothiophene and trimethylsilylacetylene led to the formation of l,2-bis(2 -thienyl)acetylene (6.47.),69... 

BOC-Amino acids. Chemists at Fluka- have prepared many of these useful derivatives of amino acids by reaction with this reagent in aqueous organic solvents with sodium hydroxide as base. In general yields arc 65 -95%. 

The alkylation of the 1,2,6-thiadiazine (76) has been studied in detail (82H(l7)40l) because of its importance as an isostere of 6-methyluracil. Dimethyl sulfate in the presence of sodium hydroxide as base gives the 2-monomethyl derivative exclusively. Other reagents such as diazomethane and iodomethane give the 2,6-dimethyl derivative as the major product although substantial amounts of O-methylation and C-methylation at C-4 also occur, indicating that in systems where there are several possible sites for alkylation, the results are very much dependent on the reaction conditions. 

In polyfluorobenzenes having other substituents in addition to fluorine, including per-fluoroalkyl or perfluoroaryl groups, the elimination of only one fluorine atom proceeds more readily, with the para position in pentafluorobenzene derivatives being replaced first. The reaction conditions used for monosubstitution of fluorine depend markedly on the substrate and on the nucleophilic agent chosen. In most cases the reaction can be carried out in ethylene glycol/pyridine using sodium hydroxide as base (Table 3). 

Multiple, but not complete, substitution of fluorine by sulfur nucleophiles proceeds under conditions rather similar to those for single elimination, i.e. generally in diethylene glycol/ pyridine mixture with sodium hydroxide as base, but with an increased molar ratio of the respective thiol, corresponding to the number of fluorines to be eliminated. On reaction in ethylene glycol/ pyridine, rather than in dimethylformamide or, particularly, in hexamethyl-phosphoric triamide, at least two fluorine atoms remain in the molecule, even under drastic... 

The successful extension of this asymmetric reaction to the use of allyl halides (instead of benzyl halides) was also reported by the Metzner group [208]. The desired vinyl oxiranes were formed in a one-pot reaction starting from an allyl halide and an aromatic aldehyde in the presence of a sulfide, e.g. 215, and sodium hydroxide as base. A 9 1 mixture of tert-butanol and water was used as solvent. 

Typically, reactions are carried out open to air, at room temperature (rt), using a mixture of tBuOH/water (9 1) or MeCN/water (9 1) as solvent and sodium or potassium hydroxide as base. The presence of water suppresses undesired side reactions (e.g., Cannizzaro reaction, Williamson alkylation, solvent reactivity) [37]. Benzyl bromides are most commonly reported as the halide component. 

The use of ammonium hydroxide as base furnishes 4-quinolinecarboxamides488, which when subjected to Hoffmann degradation conditions produce 4-aminoquinolines489. 4-Cyanoquinolines are produced when the corresponding acids are treated with 4-toluenesulfonamide and POCI3490. 

A new cyclization process was published in 2003 <2003PS1295>, where dithiols are substituted by dithioiminium salts, which can be created by reacting thioacteamide 5 with a,o -dihalides. In a second step, the dithioiminium salts 6 are treated with (different) a,tu-dihalides adding sodium hydroxide, as base, and tetrabutylammonium bromide, as phase-transfer catalyst (Scheme 2). Thus, two kinds of macrocycles are found in the final reaction mixture XS2 (1 1 ratio) 7 and (2X)S4 (2 2 ratio) 8. 

Theoretically, in a simple kinetic resolution the ee value should not exceed 32 % at this specific conversion. In addition to the rhodium complex, this reaction requires acetophenone as stoichiometric hydride acceptor, phenanthroline as coligand and potassium hydroxide as base. An ee value of 98 % at 60 % conversion (theoretical value 67 %)is achieved with [Rh2(OAc)4] without an added base after 3 days. Surprisingly, the enzyme tolerates potassium hydroxide in amounts up to 20 mol% at elevated temperatures however, the enantiomeric excesses are somewhat lower than those obtained in an ordinary kinetic resolution. Unselective, base- or metal-catalyzed acylation might be the reason for the somewhat lower ee value. 

Finally, Lieser and Thiel were able to achieve even higher average-degrees of substitution with yet another preparative innovation, the use of tetraalkylammonimn hydroxides as bases in xanthation. Thus, the product from phenyl /3-D-glucop3rranoside, carbon disulfide, and tetra-ethylammonium hydroxide corresponded in gross composition to a tri-0-(thiolthiocarbonyl) derivative and yielded, on fractionation, some fully-esterified compound. 

Alkylation of aldehydes and -keto esters, This reaction can be conducted by use of solid-liquid phase-transfer catalysis using powdered sodium hydroxide as base and benzene as the solvent. Under these conditions aldehydes with only one a -hydrogen, such as isobutyraldehyde, are alkylated in reasonable yield even by less reactive halides (equation I). 

Finally, the CH2 group between the carbonyl group and the benzene ring is acidic and can rite with hydroxide as base to form an enolate. Elimination gives a ketene that can be attacked hydroxide acting as a nucleophile to give the product. mechanism 3 enolate elimination to give a ketene... 

The critical features of the present methylation process are tb< use of only a slight excess of dimethyl sulfate over the theoretical amouri i necessary for methylation of two phenol groups, preferably about 15 ( 25% excess the use of powdered alkali metal carbonate as the base and the use of an organic solvent medium. In this manner, high yields G 3,4,5-trimethoxybenzaldehyde are obtained. This is to be compared wit prior art processes (e.g., J. Chem. Soc., London, 1930, p. 811) utilizin.. large excesses of dimethyl sulfate, alkali metal hydroxides as bases, and aqueous media, affording relatively poor yields of product. 

The Ramberg-Backlund reaction using hydroxide as base can also be performed under phase-transfer conditions, the rate of reaction varying markedly from one substrate to another (equations 2 and 3). One advantage of using these conditions is that ester groups are not hydrolyzed (equation 4 compare equation 46). 

The chemistry of sulfones is dominated by the reactions of sulfonyl carbanions. The sulfone group has a unique ability to facilitate deprotonation of attached alkyl, alkenyl and aryl groups and will permit multiple deprotonation to yield polyanions. These properties, combined with the relative intertness of the sulfone (S02) group to nucleophilic attack, have made the S02 group the first choice for stabilisation of carbanions and account for the extensive application of sulfones in synthesis. Sulfonyl carbanions can be generated and reacted under a wide variety of conditions extending from aqueous phase transfer reactions using sodium hydroxide as base to the use of alkyllithiums in polar aprotic solvents. The reactivity of sulfonyl carbanions depends on the nature of the metal counterion (Li+, Na+, K+ and Mg2+ are the most important ones) and the presence of additives, e.g. TMEDA, HMPA and Lewis acids. 

I roccdiircs for the conversion of isophoronc" (71 and 2,3-diphenylindenitn (HI into (he corresponding epoxides specify sodium hydroxide as base and methanol ur oihunol ns orgiinic sulvcnt. 

Permethylation of polysaccharides. Kuhn and Trischmann found that polysaccharides can be methylated very efficiently in DMSO with dimethyl sulfate and barium oxide and/or barium hydroxide. Srivastava et al. used the same method except for the substitution of sodium hydroxide as base. Sodium hydroxide pellets and dimethyl sulfate were added with stirring under nitrogen over 8 hrs. to a solution of undegraded stareh in dimethyl sulfoxide. After stirring for another 16 hrs. the mixture was heated to decompose the dimethyl sulfate, cooled, diluted, and neutralized, and the product was extracted with chloroform and precipitated from acetone with ether yield 91%, OCHa = 42.3%. Here the high solvent power of DMSO clearly contributes to the solvent effect. 

Preparation. The reagent is readily prepared by the condensation of benzil with dibenzyl ketone in the presence of a basic catalyst. Dilthey s original procedure, adopted by Organic Syntheses specifies ethanol as solvent and a solution of potassium hydroxide in ethanol as the base. This procedure suffers from the low boiling point of the alcohol and the limited solubility of both potassium hydroxide and the reaction product in ethanol. In an improved procedure - use of the better solvent triethylene glycol permits operation at a higher temperature, and use of the readily soluble benzyltrimethylammonium hydroxide as base eliminates the step of dissolving potassium hydroxide in ethanol, A mixture of 0.2 mole each of benzil and... 

A bicyclic aromatic ring system provides additional stabilization of the anionic a-adducts hence, nitronaphthalene derivatives show good reactivity in the VNS hydroxylation. 1-Nitronaphthalenes give 2- and 4-hydroxy derivatives in high yields. The orientation of the hydroxylation depends on the kind of base. For instance, treatment of 1-nitronaphthalene (15) with f-butyl hydroperoxide and potassium t-butoxide affords l-nitro-2-naphthol (16) whereas using sodium hydroxide as base gives 4-nitro-l-naphthol (14) (equation 34) . 

Dichlorocyclopropanes have been converted to l,l-bis(phenylsulfanyl)cyclopropanes in good yield under phase-transfer conditions using sodium hydroxide as base, benzene as organic solvent, and tetrabutylammonium bromide or benzyltriethylammonium chloride as catalyst. Typically, ler/-butyl 2,2-bis(phenylsulfanyl)cyclopropanecarboxylate (3) was obtained in 71 /o yield from tert-butyl 2,2-dichlorocyclopropanecarboxylate by this method. ... 

Methylation of aryl thiols. PTC methylation of l C-aryl thiols with methyl Iodide (2 ) Is very useful for microscale synthesis of C-labeled aryl methyl sulfides (2j ). The reaction, using tetrabutylammonlum hydrogensulfate as catalyst and sodium hydroxide as base In methylene chloride and water, proceeds at ambient temperature In 50-100Z yield. 

The selectivity (C-2 C-4 2,4-disubstitution) of Suzuki couplings of 2,4-dibromopyridine varies greatly with catalyst and conditions. The most selective C-2 mono-coupling is obtained using Pd(PPh3)4 with thallium hydroxide as base. (Caution Thallium hydroxide is very toxic.)... 

From the development of resonance lines in the different spectra, a qualitative reaction mechanism can be extracted for the oligomerization process. In this mechanism, formation of cyclic structures is a predominant phenomenon. In the presence of TMA cations, no linear trimeric silicate anions are found in the silicate solutions, as can be deduced from Figures Id through lh. The use of alkali metal hydroxides as bases shows, aside from the cyclic trimeric silicate anion, the linear structure the relative concentration of each depends on the alkalinity and the alkali metal used. The formation of cyclic trimeric silicate anions occurs before formation of the linear trimeric species (6). The formation of double-cyclic silicate anions can be observed in Figure le two cyclic trimeric silicate anions combine to form the prismatic hexameric silicate anion (Q36). This prismatic hexameric silicate anion forms, through addition of two monomers or one dimer, the well-known cubic octameric silicate anion. This cubic octameric silicate anion has been proposed to be predominantly... 

---