Cesium carbonate, reaction with

In the series of the alkali metal carbonates and -hydroxides the cesimn compounds are the strongest bases [14]. For reasons of simpler handling the less hygroscopic carbonate is often preferred to the hydroxide. In dipolar aprotic solvents, carboxylic acids [15], phenols [16], thiols [17, 18] and sulfonamides [19] are easily deprotonated by cesium carbonate, whereas with carbamates such as e.g. benzyloxycarbonyl- ( Z -)protected amino acids no reaction occurs [20]. 

Amides and ureas The sulfonamides undergo functional group exchange on reaction with thiolacetic acid, hydroxamic acids, and R2NC(=S)SH, in the presence of cesium carbonate. Reaction of the sulfonamides with dithioacids affords thioamides. 

Similar olefination reactions were performed in weakly hydrated solid/liquid media (Mouloungui et ai, 1989). Depending on the nature of the solid inorganic base, the presence of small amounts of water was able to promote the olefination reaction. For example, potassium carbonate allows the reaction of furfural with ethyl (diethylphosphono)acetate in the presence of one or two equivalents of water, whereas no effect is observed for the cesium carbonate reaction. 

The most demanding test of cesium carbonate as base was with 2,3-dihydroxypyridine (3-hydroxypyridone). The cesium salt was found to be fairly unstable, apparently oxidizing quite rapidly. Model reactions suggested that alkylation would occur 1,3 (N, 0) to give the substituted pyridone. Nevertheless, on the basis of UV and H-nmr analysis, the product of reaction between 2,3-dihydroxypyridine and tetraethylene glycol dibromide was assigned as the pyridocrown (23% yield, mp 77—78.5°) as shown in Eq. (3.60). 

Carbon-nitrogen multiple bonds in fluorinated imines and nitriles react with halogen fluoride reagents Imines provide 7V-chloroamine.s on reaction with chlo rme fluoride [62, 121, 122, 123] (equations 23 and 24) or with cesium fluoride and chlorine [124] and A -bromoammes on reaction with cesium fluoride and bromine (equation 24)... 

This reaction is similar to 13-1 and, like that one, generally requires activated substrates. With unactivated substrates, side reactions predominate, though aryl methyl ethers have been prepared from unactivated chlorides by treatment with MeO in HMPA. This reaction gives better yields than 13-1 and is used more often. A good solvent is liquid ammonia. The compound NaOMe reacted with o- and p-fluoronitrobenzenes 10 times faster in NH3 at — 70°C than in MeOH. Phase-transfer catalysis has also been used. The reaction of 4-iodotoluene and 3,4-dimethylphenol, in the presence of a copper catalyst and cesium carbonate, gave the diaryl ether (Ar—O—Ar ). Alcohols were coupled with aryl halides in the presence of palladium catalysts to give the Ar—O—R ether. Nickel catalysts have also been used. ... 

Synthesis of 5,10,15,20-Tetrakis(4-(polyethyleneoxy)phenyl)) porphyrin. A slurry of polyethylene methylsulfonic ester (PEvoo-OMs) (20.0 g, 69% functionalized, Mn -780 Daltons) and anhydrous cesium carbonate (CS2CO3) (9.05 g, 27 mmol) in dry toluene (75 ttiL) was prepared and to this mixture a purple solution of 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphine (2.9 g, 4.27 mmol) in 75 mL A. A-DMF was added. The reaction mixture was warmed to 95°C with stirring for 18 hours, then the temperature increased to 130°C for a further 5 hours before coohng. The purple-brown solid was collected by filtration, washed thoroughly with methanol and dried under vacuum to yield 21.0 g of the crude ligand, h NMR (toluene-dg, 80°C) 5 8.96 (s), 8.10 (d), 7.22 (d), 4.05 (t), 1.88 (quia), 1.58 (quin.), 1.31 (br. s), 0.88 (t). 

For the installation of the pyrrolidinylethanol moiety 10 on the aryl group, we first tested Buchwald s Cu-catalyzed conditions with 10, aryl iodide 12, Cs2C03, Cul and 1,10-phenanthroline at 110°C in toluene to prepare the penultimate 49 [14a], The reaction was very slow, giving only 5-10% conversion even after 2 days. The reaction was faster at higher temperatures but two impurities 50 and 51 were observed (Scheme 5.14). To find the optimal conditions, xylene and diglyme were tested as solvents, lithium, potassium and cesium carbonates were screened as bases and 2,2 -bipyridy], TMEDA and l-(2-dimethylaminoethyl)-4-methylpiperazine were examined as ligands. The optimized protocol was identified as 10mol% of... 

With the nitro group successfully introduced, the aromatic fluoride substituent in 11 was ready to undergo the nucleophilic aromatic substitution with the hydrox-ypyridine 9. The reaction proceeded smoothly in DMF at 55 °C using an equimolar amount of cesium carbonate as the base and provided a 90% isolated yield of 23 after crystallization. With compound 23 in hand, only the reduction of the nitro... 

Another example where PEG played the role of polymeric support, solvent, and PTC was presented by the group of Lamaty [72]. In this study, a Schiff base-proteded glycine was reacted with various electrophiles (RX) under microwave irradiation. No additional solvent was necessary to perform these reactions and the best results were obtained using cesium carbonate as an inorganic base (Scheme 7.64). After alkylation, the corresponding aminoesters were released from the polymer support by transesterification employing methanol in the presence of triethylamine. 

Dithiocarbamates have been prepared by the reaction of carbon disulfide with primary or secondary amines. The addition of DMF, cesium carbonate and a sulfonamide to the crude dithiocarbamate, give di-, tri- and tetra-substituted thioureas in 65-76% yields (Scheme 41).121... 

General procedure - with telluronium salt method A mixture of trimethylsilylprop-2-enyl(di-isobutyl)telluronium bromide (0.33 g, 0.75 mmol), cesium carbonate (0.25 g, 0.75 mmol), chalcone (0.5 mmol), and DME (5 mL) and water (5 mm ) was heated at 70°C for specific periods of time. When the reaction was complete (monitored by TLC), the resulting mixture was eluted with ethyl acetate through a short column of silica gel. Removal of the solvent and flash chromatography on silica gel gave the desired pure product, of purity >98% (GC). 

THF solution containing aqueous cesium carbonate. The reaction of [2.2.1]oxabicycle 37b with phenylboronic acid 2m gave the ring-opened alcohol 38bm, with 95% enantiomeric excess. 

In terms of A -substitution, Hartwig reported improved conditions for the Pd(0) catalyzed N-arylation of indoles and pyrrole <99JOC5575>. It was found that when commercially available P(<-Bu)3 was employed as ligand and cesium carbonate as base, the reaction between indoles 95 and unhindered aryl bromides 96 or chlorides occurred under milder conditions than the Pd(OAc)2/DPPF system previously reported yielding the A/-arylated products 97. Alternatively, it has been found that pyrrole- and indole-2-carboxylic acid esters can be selectively 7V-arylated with phenylboronic acids in the presence of cupric acetate and either tiiethylamine or pyridine <99T12757>. 

A 2L round-bottomed flask with a magnetic stirrer bar and a 3-way tap with argon balloon was charged with 2,2, 6,6 -tetrahydroxybiphenyl (4.4 g, 20.2 mmol), cesium carbonate (15.2 g, 46.5 mmol) and A,M-dimethylformamide (780 mL). The mixture was heated to 80 °C. To the mixture was slowly added (S)-1,2-propanediol bismesylate (2.74 g, 14.5 mmol) in A,M-dimethylformamide (6mL) over 4h, and this was stirred for 1 h at the same temperature (TLC hexane/ethyl acetate =1/1, product Rf= 0.5). After cooling to 0 °C, the reaction mixture was quenched by 1 M aqueous hydrochloric acid (150 mL). 

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