Potassium-catalyzed reactions

The reactions of oxiranes with thiocyanate ion or with thiourea are usually done in homogeneous solution in water, alcohols or alcohol-acetic acid. The use of silica gel as a support for potassium thiocyanate in toluene solvent is advantageous for the simple work-up (filtration and evaporation of solvent) (80JOC4254). A crown ether has been used to catalyze reactions of potassium thiocyanate. 

Most commercial liquid ammonia contains up to several ppm of colloidal iron compounds, possibly the iron oxide catalyst commonly used in manufacturing ammonia. Reduction converts these compounds to colloidal iron which strongly catalyzes the reaction between alcohols and sodium and potassium. The reaction of lithium with alcohols is also catalyzed by iron but to a markedly lesser degree. The data in Table 1-4 illustrate the magnitude of these catalytic effects. The data of Table 1-5 emphasize how less than 1 ppm... 

The mercaptals obtained by the acid catalyzed reaction of J3-ketoesters, e.g., ethyl acetoacetate, with methyl thioglycolate (73) undergo the Dieckmann cyclization with alcoholic potassium hydroxide at lower temperatures to give ethyl 3-hydroxy-5-methyl-2-thiophenecarboxylate (74) in 75% yield. ° Besides ethyl acetoacetate, ethyl a-ethylacetoacetate, ethyl benzoyl acetate, and ethyl cyclopentanonecarboxylate were also used in this reaction/ It is claimed that /8-diketones, hydroxy- or alkoxy-methyleneketones, or /8-ketoaldehyde acetals also can be used in this reaction. From acetylacetone and thioglycolic acid, 3,5-dimethyl-2-thiophenecarboxyl-ic acid is obtained. ... 

Sodium or potassium phenoxide can be carboxylated regioselectively in the para position in high yield by treatment with sodium or potassium carbonate and carbon monoxide. Carbon-14 labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product. The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compoimds as catalysts. In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH —> ArCOF. ... 

Bromobenzyl groups were introduced into PPO by radical bromination of the methyl groups. The PPO bromobenzyl groups and PECH chloromethyl groups were then esterified under phase-transfer-catalyzed reaction conditions with the potassium carboxylates just described. This procedure has been described previously (29). The sodium salt of 4-methoxy-4 -hydroxybiphenyl was also reacted with PECH (no spacer). 

Jenner investigated the kinetic pressure effect on some specific Michael and Henry reactions and found that the observed activation volumes of the Michael reaction between nitromethane and methyl vinyl ketone are largely dependent on the magnitude of the electrostriction effect, which is highest in the lanthanide-catalyzed reaction and lowest in the base-catalyzed version. In the latter case, the reverse reaction is insensitive to pressure.52 Recently, Kobayashi and co-workers reported a highly efficient Lewis-acid-catalyzed asymmetric Michael addition in water.53 A variety of unsaturated carbonyl derivatives gave selective Michael additions with a-nitrocycloalkanones in water, at room temperature without any added catalyst or in a very dilute aqueous solution of potassium carbonate (Eq. 10.24).54... 

Another domino Heck/Diels-Alder process described by the same group [64] implies the Pd°-catalyzed reaction of 6/1-118 in the presence of acrylate or methyl vinyl ketone to give the corresponding bicyclic compounds 6/1-120 and 6/1-121 via the transient 6/1-119 (Scheme 6/1.32). Good yields were obtained only if potassium carbonate is used as base. 

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]. 

Kuroda and Suzuki used reaction of 267a with 2-bromoaniline leading to anilide 312 as the first step of their sequence in the preparation of 1H-imidazo[4,5-c]quinolin-4(5//)-ones (Scheme 77) (91TL6915). Reaction of 267a with amines usually does not require any catalyst and/or base, but in this case use of sodium hydride was reported. The anilide 312 was sequentially alkylated, first with methyl iodide in ethanol with potassium hydroxide at room temperature and then with different alkyl iodides in acetone at reflux to provide intermediate 313. This compound was then cyclized via palladium catalyzed reaction leading to product 314. This reaction provides a new entry to l//-imidazo[4,5-c]quinolin-4(5//)-ones that are of current interest as antiasthmatic agents. 

In 1991, Mandai et al. reported that the palladium-catalyzed reaction of propargyl carbonates with olefins proceeded smoothly in DMF at 70 °C in the presence of triethylamine and potassium bromide to give vinylallenes in good yields [54], The active palladium catalyst was generated in situ from Pd(OAc)2 and PPh3. A typical example is shown in Scheme 3.19. 

Only Cram (36) has published a rationale for the very high (99%) enantiomeric excess achieved in the reaction of methyl vinyl ketone and the hydrindanone in the presence of the chiral crown ether. This mechanism envisions a bimolecular complex comprising the potassium cation and chiral host as one entity and the enolate anion of the hydrindanone as the counterion. Methyl vinyl ketone lies outside this complex. The quinine-catalyzed reaction appears to have a termo-lecular character, since the hydroxyl of the alkaloid probably hydrogen bonds with the methyl vinyl ketone—enhancing its acceptor properties—while the quin-uclidine nitrogen functions as the base forming the hydrindanone—alkaloid ion pair. 

Table I. Effect of Cation on PVP Catalyzed Reaction of Sodium or Potassium Cresoxide with 4-Chloronitrobenzene ...

The observed catalytic effect of the crown ether appears to be dependent on the nucleophile employed in both polymerization and corresponding model reactions. Not surprisingly, it appears that the stronger the nucleophile employed, the smaller the catalytic influence of the crown ether. For example, with potassium thiophen-oxide yields of polymer or model products were almost quantitative with or without catalyst. By contrast, the reaction of PFB with potassium phthalimide, a considerably weaker nucleophile, affords 6 in 50% with catalyst and in 2-3% without catalyst under identical conditions. However, it may be that this qualitative difference in rates is, in fact, an artifact of different solubilities of the crown complexed nucleophiles in the organic liquid phase. A careful kinetic study of nucleophilicity in catalyzed versus non-catalyzed reactions study is presently underway. 

Seignette salt See potassium sodium tartrate. sen yet, s6lt selective inhibition See selective poisoning. sl lek tlv. In a bish-an selective poisoning chem Retardation of the rate of one catalyzed reaction more than that of another by the use of a catalyst poison. Also known as selective inhibition. si lek-tiv poiz-an-it) ... 

Acid-catalyzed reactions of aromatics with monoolefins result in nuclear alkylation. But the base-catalyzed reactions of aromatics with olefins do not result in nuclear alkylation as long as benzylic hydrogens are available. This is true even with aromatics, such as cumene, which have deactivated benzylic hydrogens resulting in facile metalation of the ring. Apparently phenyl carbanions do not readily add to olefins. Pines and Mark (20) found that in the presence of sodium and promoters only small yields of alkylate were produced at 300° in reactions of benzene with ethylene and isobutylene and of t-butylbenzene with ethylene. With potassium, larger yields may be obtained at 190° (24)-... 

A common and effective direct approach to unsubstituted or multiply substituted oxazolines is the Lewis acid catalyzed reaction of nitriles with amino alcohols in an alcoholic or aromatic solvent (chlorobenzene) at reflux. The most common Lewis acids employed include ZnCl2, ZnBr2, NiBr2, CuCl2, and kaolinitic clay. Microwave irradiation has also been reported to facilitate the transformation. Alternatively, the condensation can be carried out in the presence of catalytic amounts of potassium carbonate. The method works well for both aliphatic and aromatic nitriles, with retention of stereochemistry. Some representative examples from the recent literature are listed in Table 8.16 (Scheme 3 40),2 35.2oi-2i3... 

The oxidations involving lithium ferf-butoxide reach completion (3 minutes for fluorenol, 12 minutes for xanthenol) much sooner than the corresponding reactions utilizing potassium terf-butoxide as base (35 minutes for fluorenol, 27 minutes for xanthenol). This behavior obviously involves Reaction 20 since the initial rates of oxidation were all approximately the same for the lithium- and potassium ferf-butoxide-catalyzed reactions. 

Acid- or base-catalyzed retro-aldolization of protected 7-hydroxybicyclo[5.2.0]nonane-l-carb-oxylates afforded bridged cyclononanone derivatives.14 Methyl esters were found in the /j-toluenesulfonic acid catalyzed reaction in refluxing methanol to give la and 2, whilst the free acid lb was formed with potassium hydroxide.14... 

The addition of chlorine monofluoridc across the C = 0 bonds in difluorophosgene, per-fluoroacyl fluorides, and perfluoroketones with the formation of hypochlorites occurs only in the presence of the catalysts potassium fluoride, rubidium fluoride, cesium fluoride80,81 or the strong Lewis acids hydrogen fluoride, boron trifluoride, or arsenic(V) fluoride.82 The cesium fluoride catalyzed reactions are carried out in an autoclave for 2-3 hours at — 20"C or left overnight.80... 

Peracetic acid decomposition kinetics in the presence of cobalt or copper acetates were studied in the same apparatus used for the manganese-catalyzed reaction. However, in these studies it was used as a batch reaction system. The reactor was charged with peracetic acid (ca. 0.5M in acetic acid) and allowed to reach the desired temperature. At this time the catalyst (in acetic acid) was added. Samples were withdrawn and quenched with potassium iodide at measured time intervals. 

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