Potassium carbonate as base

Many reactions have been shown to benefit from irradiation with ultrasound (ref. 19). We therefore decided to investigate the effect of ultrasound, different catalysts and the presence of solids on Ullmann diaryl ether synthesis. Indeed, sonication of mixtures of a phenol and a bromoaromatic compound, in the absence of solvent and presence of copper (I) iodide as catalyst and potassium carbonate as base, produces good yields of diaryl ethers at relatively low temperatures (Fig. 10) (ref 20). 

A new comparison of the copper and nickel catalysts (Fig. 12) on the arylation of alcohols, using potassium carbonate as base, shows once again the superiority of the nickel catalyst (70 % against 40 % for the copper catalyst). 

Selective retro-aldol has also been reported by using aqueous HC1 in THF.243 Recently, catalytic aldol reactions in aqueous media have generated great interest due to the atom-economy related to the reaction. Reaction of 2-alkyl-1,3-diketones with the aqueous formaldehyde using aqueous 6-10 M potassium carbonate as base afforded aldol reaction products, which are cleaved by the base to give vinyl ketones (Eq. 8.96).244... 

The approach also allows the synthesis of furans by employing ethoxymethylene malonate, followed by an eliminative decarboxylation. This method was used by Balme for a formal synthesis of the antitumor lignan burseran (6/1-294), starting from 6/1-290,6/1-291 and 6/1-292 via the furan 6/1-293 (Scheme 6/1.78) [139], Furans as 6/1-298 can also be obtained by Pd-catalyzed reaction of 2-propynyl-l,3-dicarbonyls 6/1-295 with aryl halides 6/1-296 in DMF, using potassium carbonate as base, as shown by Arcadi, Cacchi and coworkers (Scheme 6/1.79) [140]. 

The same reactions, carried out with potassium carbonate as base in place of a secondary amine, yield exocyclic dienes in good yield, although double-bond isomerization sometimes occurs (equation 38).93 Inclusion of tetra-zi-butylammonium chloride in the reaction mixture stops the double-bond isomerization. Thus, the reaction in equation (38) with the chloride yields only the bis(exomethylene) product in 45% yield in a slow reaction. Some N- and O-heterocyclic products, also, have been prepared by the intramolecular vinyl substitution reaction.94 A 16-membered ring lactone was made by the ring closure of a vinylic iodide group with a vinyl ketone group. The yield, based upon the reactant, was 55% but a stoichiometric amount of bis(acetonitrile)palladium dichloride was employed. The catalyst was prereduced with formic acid so that the reaction proceeded at 25 C (equation 39).95... 

Starting material 8 is treated with the propargylic bromide 9 in the presence of potassium carbonate as base in a nucleophilic substitution, producing compound 10... 

It has been shown that combination of bromoallylation reaction and Heck cyclization is a useful methodology for the preparation of a variety of fused bicyclic (3-lactams of nonconventional structure [95], Starting from acetates 164 and using palladium acetate as the palladium source, DMF as solvent, potassium carbonate as base, and triphenylphosphine, the reaction occurred. The reaction conditions were further optimized and typical results for the preparation of bicyclic (3-lactams 165-168 are summarized in Schemes 57. 

Treatment of the sodium salt of 2-cyanocyclododecanone (VII/109) with a>-haloisocyanates yields the 14-membered imide VII/U2. Two cyclization products of VII/112 were obtained in the presence of potassium carbonate as base. In the C-alkylated bicycle, VII/113, the central bridge bond is solvolyzed to form the 16-membered amide VII/114. The O-alkylated bicycle, VII/US, which is the minor product, was not investigated further. When 2-chloroethyl isocyanate was used as reagent, the analogue of VII/115 was formed directly. Because of its multistepcharacter the reaction resembles MIMIRC (Scheme VII/9) [59] [60]. 

Furans as 6/1-298 can also be obtained by Pd-catalyzed reaction of 2-propynyl-l,3-dicarbonyls 6/1-295 with aryl halides 6/1-296 in DMF, using potassium carbonate as base, as shown by Arcadi, Cacchi and coworkers (Scheme 6/1.79) [140]. 

Dilution reactions in concentrated solution [88] A method applied successfully by Schneider [88] in the synthesis of tosylaza macrocycles consists in the reaction of tosylamides with bromides in DMF using potassium carbonate as base. Here K2CO3 compared with CS2CO3 has the advantage of lower solubility (ca. 10 M). Thus more concentrated solutions of the reactants can be added to a suspension of the base in DMF. The low solubility of K2CO3 causes only a small amount of the reactive tosylamide anion to be present at all times, securing the dilution effect. 

This reaction can be conducted under solid-hquid phase transfer catalytic (PTC) conditions using sohd potassium carbonate as base and a liquid lipophihc quaternary ammonium salt as catalyst. Numerous carbodiimides with a side chain bearing a tertiary amino group, such as-(CH2) NMe2, are obtained in this manner. Sheehan and cowoikers used a modification of this procedure to synthesize several water soluble carbodiimides. ... 

A typical preparation of the polycarbonates is shown for polymer III in Scheme I. 1,4-Benzenedimethanol is activated by reaction with two equivalents of p-nitrophenyl chloroformate in pyridine and the resulting symmetrical dicarbonate is then used in a polycondensation with an equimolar amount of 2-cyclohexen-l,4-diol in a solid-liquid phase-transfer catalyzed reaction with 18-crown-6 as catalyst and solid anhydrous potassium carbonate as base. Alternately, the same polymer can be prepared by condensation of bis(4-nitrophenyl)-2-cyclohexen-1,4-ylene dicarbonate [12] with 1,4-benzenedimethanol or through a variety of similar polycondensations using diol biscar bonylimidazolides [13,14]. 

Michael addition to a, -unsaturated aldehydes The Michael addition of malonic ester and acetoacetic ester to a,0-unsaturated aldehydes can be carried out in moderate yields under phase-transfer conditions with sodium or potassium carbonate as base and benzyltriethylammonium chloride as catalyst (equation I). 

The stretched porphycenes have shown some promise as ligands for the com-plexation of transition metal cations. For instance, when [22]tetradehydroporphyrin-(2.2.2.2) 4.115 is treated with di-p-chlorobis[dicarbonylrhodium(I)] in dichloro-methane using potassium carbonate as base, a bis[Rh(CO)2] complex is formed. ... 

The phenolic hydroxy group is first protected using benzyl chloride and potassium carbonate as base to avoid an oxidation of p-dihydro-phenols to the corresponding p-benzoquinones. 

Activation with sulfonic acid chlorides is more general, rendering amides with the possible participation of symmetric anhydrides after disproportionation. This method has also found use in the synthesis of modem 3-lactam antibiotics. However, in peptide chemistry this activation method leads to unwanted side reactions, like formation of nitriles in the cases of glutamine and asparagine, and racemization. In a convenient one-pot procedure, the carboxylic acids are activated by sulfonyl chlorides under solid-liquid phase transfer conditions using solid potassium carbonate as base and a lipophilic ammonium salt as catalyst. ... 

The additive natures of electronic and steric factors are obvious in the methylation, ethylation, and benzylation of 4-nitroimidazole (see Table 8). It seems that the dominant electronic effects of substituents are inductive since mesomeric effects affect electron density both a and y to the substituent. Inductive effects will mainly be felt on the nitrogen adjacent to the substituent (R ). Hammett correlations are also much better with CTm or u, than Cp constants <94H(37)735>. When alkylations were carried out in DMF with potassium carbonate as base, again electron-attracting... 

Sinou and co-workers [73] studied the influence of different surfactants on the palladium-catalyzed asymmetric alkylation of l,3-diphenyl-2-propenyl acetate with dimethyl malonate in presence of potassium carbonate as base and non-water-soluble chiral ligands. Best results in activity and enatioselectivity (> 90% ee) were observed with 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP) as ligand and cetyltrimethylammonium hydrogen sulfate as surfactant in aqueous medium. Water-stable Lewis acids as catalysts for aldol reactions were developed by Kobayashi and co-workers [74]. An acceleration of the reaction was indicated in presence of SDS as anionic surfactants. An additional promotion could be observed by combination of Lewis acid and surfactant (LASCs = Lewis acid-surfactant-combined catalysts) as shown in Eq. (3). Surfactant the anion of dodecanesulfonic acid. 

Furthermore, Bumagin and Beletskaya reported the first coupling in neat water in the presence of a small amount tributylamine (10 mol%) and potassium carbonate as base [23], Surprisingly, the catalyst system consists of water-insoluble tri-phenylphosphine with PdCl2 and Cul at room temperature, resulting in high yields with aryl iodides and phenylacetylene. The role of cuprous iodide was noted to be important to facilitate the reaction, which may be rationalized by two connected catalytic cycles (Scheme 2). 

Dihydro-1,4-diazepines are strongly basic (pA a ca. 13-14) and readily react with adds to form diazepinium salts, the chemistry of which has been studied extensively <93AHC(56)i>. N-Unsubstituted 2,3-dihydro-1,4-diazepinium salts are alkylated on both N atoms upon treatment with alkyl halides in DMF using potassium carbonate as base <86LA1387>. For steric reasons the presence of large substituents in the 5- and 7-positions can limit this reaction to alkyl halides with small alkyl groups. 

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