Potassium cyanide/18-crown-6 complex

Chromium trioxide, 21 Clemmensen reaction, 111 18-Crown-6-potassium cyanide complex, 129... 

Chromium trioxide, 60, 21 Clemmensen reaction, 60, 111 Copper chloride (CuCl) [7758-89-6], 61, 122 Crotonic acid, ethyl ester, ( )-, 61, 85 18-Crown-6-potassium cyanide complex, 60,129 Crum Brown-Walker reaction, 60, 4 Cuprous chloride, 60, 42, 121 61, 122 CYANIC ACID, PHENYL ESTER [1122-85-6], 61, 35... 

The potassium cyanide complex of 18-crown-6 in benzene or acetonitrile undergoes Michael addition to unsaturated carbonyl compounds (Liotta et al., 1977). In the presence of acetone cyanohydrin, the catalytic (i.e. catalytic in potassium cyanide and crown ether) cycle for hydrocyanation shown in (21)... 

Hydroxy linkers bearing an electron-withdrawing group such as an a-carbonyl (oxyacyl resins, phenacyl type-linkers or glycolic acid derivatives) are also suitable for the nucleophilic release of ester bound compounds. The glycolamidic ester linker 10 has been successfully used to synthesize peptides by the Fmoc/tBu strategy. It is compatible with the repetitive piperidine treatment but peptides can be cleaved with dilute NaOH solutions, ammonia or alkoxides [9], Esters bound to oxyacyl resins 8 have been reported to be cleavable by thiolysis, saponification, ammonia, hydrazine and potassium cyanide (complexed with dicyclohexyl-18-crown-6) [10, 11],... 

Photochemical cyanation of aromatic hydrocarbons in acetonitrile solution is a higher yield process when the potassium cyanide complex of 18-crown-6 is the cyanide ion source [31] compared to similar reactions in mixed organic aqueous solvent systems [32] (see Eq. 7.16). A ten-fold excess of 18-crown-6/KCN over the aromatic hydrocarbon (present in 10 " M) was used. The yield improvements were attributed to increased activity of cyanide due to diminished hydration of the ion. Biphenyl, naphthalene, phenanthrene, and anthracene were photocyanated in 50%, 15%, 25% and 20% yields respectively the latter being an equimolar mixture of mono and dicyanation products [31]. 

A typical phase transfer catalytic reaction of the liquid/liquid type is the cyanation of an alkyl halide in an organic phase using sodium or potassium cyanide in an aqueous phase. When these phases are stirred and heated together very little reaction occurs. However, addition of a small amount of crown ether (or cryptand) results in the reaction occurring to yield the required nitrile. The crown serves to transport the cyanide ion, as its ion pair with the complexed potassium cation, into the organic phase allowing the reaction to proceed. 

There have been reports of syntheses of cyano complexes in fused potassium cyanide, though the characterization of the products has not always been satisfactory.1 The dry reaction between potassium cyanide and potassium hexaiodoplatinate(IV), however, certainly gives the impure hexacyano-platinate(IV) and substitution of cycloocta-1,5-diene bonded to platinum(II) may be achieved by the use of solid potassium cyanide in the presence of a crown ether catalyst.16... 

The 1 1 complex is conveniently prepared by dissolving 0.652 g (10 mmol) of pulverized potassium cyanide and 2.640 g (10 mmol) of commercial 18-crown-6 (Aldrich Chemical Company, Inc.) in 45 mL of anhydrous methanol by swirling and warming. The methanol is then evaporated at a rotary evaporator and the white complex dried in vacuo over night. 

In a limited number of cases, arylsilanes react with aldehydes as if they were aryl Grignard or aryllithium reagents. Both trimethyl(perchlorophenyl)silane and trimethyl(perfluoro-phenyl)silane react with benzaldehyde to give the corresponding 7.-(pcrhalophenyl)bcnzyl tri-methylsilyl ethers.163 Benzaldehyde reacts completely with trimethyl(perfluorophenyl)silane in diethyl ether in the presence of either a catalytic amount of the potassium cyanide/18-crown-6 complex in less than 5 hours at room temperature or potassium fluoride in dimethylform-umide.164 In the case of aryltrimcthylsilanes containing electron-withdrawing substituents in the ortho position, the reaction is observed only under the conditions of nucleophilic catalysis by potassium fluoride or cesium fluoride. 

A crown ether can facilitate substitution between an unactivated aryl chloride and potassium methoxide. Thus, heating a solution of the dicyclohexyl-18-crown-6 complex of potassium methoxide in o-dichlorobenzene at 90° gives rise to 40—50% of o-chloroanisole, Eq. (3). No reaction is observed in the absence of the ether.25 This approach is not always successful, however. The same ether failed to induce a reaction between potassium cyanide and o-dichlorobenzene in acetonitrile.24 ... 

In the presence of a catalytic amount of potassium cyanide-18-crown-6 complex, treatment of C6F5-SiMe3 with enolizable ketones, gives the corresponding trimethylsilyl enol ethers (ref. 30). 

The use of ethyl cyanoformate as cyanide source for the addition to aldehydes has also been realized under the catalysis of [(salen)Ti( x-0)]2 (5 mol%), leading to the corresponding cyanohydrin carbonate with improved enantiomeric excesses (76-99% ee) [219]. In the presence of the potassium cyanide or the potassium cyanide/18-crown-6 complex as a cocatalyst, the catalyst can be further decreased to 1-2 mol% in the reaction system with comparable enantioselect vities [220] (Scheme 14.90). 

Reactions with Oxiranes, Oxetanes, and Aziridines. Lewis acids, lanthanide salts, and titanium tetraisopropoxide or aluminum isopropoxide catalyze the reactions of cyanotri-methylsilane with oxiranes, oxetanes, and aziridines, yielding ring-opened products. The nature of the products and the regio-selectivity of the reaction are primarily dependent on the nature of the Lewis acid, the substitution pattern in the substrate, and the reaction conditions. Monosubstituted oxiranes undergo regiospe-cific cleavage to form 3-(trimethylsiloxy)nitriles when refluxed with a slight excess of cyanotrimethylsilane in the presence of a catalytic amount of potassium cyanide-18-crown-6 complex (eqs 8-10). The addition of cyanide occurs exclusively at the least-substituted carbon. 

The mono-cyanosilylation of quinones is recorded in Table 7.7. The aldol condensatior of ethyl a-trimethylsilyldiazoacetate with aldehydes (Eq. 7.15) was found to be catalyzed by the 18-crown-6 complex of potassium cyanide [30]. A mechanism involving the diazoester enolate anion has been proposed. Several examples of this condensation have been recorded in Table 7.8. 

Many organic reactions which involve ionic species involve the cations associated with the reactive anions, even though most of the attention is focused on the latter. Some reactions, like the displacement of bromide by cyanide in the synthesis of a cyano-alkane [5] (see Eq. 7.2), appear to involve the cation in only the most peripheral way. In the above example, replacing sodium cyanide by tetrabutylammonium cyanide [6,7] or the 18-crown-6 complex of potassium cyanide does not alter the course of the reaction [8, 9], only its rate. There are, however, quite a few examples now available of alterations in the course of the reaction in the presence of crown ether, cryptate, or ammonium salts. 

The substitution reaction of cyanide with benzyl bromide (Table 1) was evaluated with and without silacrown promoted catalysis and compared with 18-crown-6 and decamethylcyclopentasiloxane (Dj). Reaction conditions and times were not optimized. The catalytic activity of the sila-17-crown-6 appeared to be equivalent to 18-crown-6. Dodecamethylcyclopentasiloxane did not demonstrate catalytic activity. The specificity of the sila-14-crown-5 for sodium ions and not potassium ions provides evidence for complex formation analogous to the crown ethers. 

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