Quaternary ammonium phenoxide

Diastereo- and enantio-selective cascade of Michael addition and lactonization between various silyl enolates derived from phenyl carboxylates and -unsaturated ketones were successfully carried out by using an efficient organic catalyst, a cinchoni- dine-derived chiral quaternary ammonium phenoxide. In this asymmetric domino reaction, the corresponding tnms-3,4-dihydropyran-2-oncs were obtained in high yields with almost complete diastereoselectivities and good to excellent enantioselectivities.161... 

Homogeneous Catalysis with Chiral Quaternary Ammonium Phenoxides... 

Recently, Mukaiyama and co-workers prepared cinchona alkaloid-derived chiral quaternary ammonium phenoxide-phenol complex 23 and used it as an efficient organocatalyst for the tandem Michael addition and lactonization between oc,f-unsaturated ketones and a ketene silyl acetal 24 derived from phenyl isobutyrate. This approach permits the highly enantioselective synthesis of a series of 3,4-dihydropyran-2-ones (25), as shown in Scheme 4.11 [17]. 

Cinchonidine-derived quaternary ammonium phenoxides (e.g., 296) have been shown to catalyze vinylogous aldol-type reaction between benzaldehyde and 4-methyl-2-(trimethylsilyloxy)furan, leading to the formation of a 5-substituted butenolide in good yield and good ee% as can be seen in Equation (181) <2007CL8>. 

In a paper that described a detailed preparation of air-stable cinchona alkaloid-derived chiral quaternary ammonium phenoxides, the Mukaiyama group also used these to enantioselectively prepare 3,4-dihydropyran-2-ones 160 [85]. A low loading of organocatalyst 159 at low temperatures, in a series of solvents, resulted in the formation of the optically active lactone products in high yields with excellent control of enantio- and diastereoselectivity. This process was proposed to go through a phenoxide-ion-catalyzed domino Michael addition and lactonization catalytic cycle as illustrated below. Many variations of the ketene silyl acetals and a, -unsaturated ketones were combined in this domino process (Scheme 7.32). Earlier,... 

The first observation made was of a chemical reaction between the epoxy and the tertiaiy amine. Sorokin and Shode observed the formation of a quaternary ammonium phenoxide in stoichiometric concentrations of epoxy and amine, which was due to the reaction of the epoxy with the tertiary amine. No product of the epoxyphenol reaction was noted ... 

It is interesting to note that the very widely used Makosza catalyst , benzyl triethyl ammonium chloride, does not show high efficiency in this study. 4) Phosphonium ions are somewhat more effective and thermally stable than the corresponding ammonium catalysts and both are better than arsonium systems. 5) Substitution of the quaternary ion by alkyl rather than aryl groups yields more effective catalysts. 6) Reaction rates are generally greater in orf/io-dichlorobenzene (and presumably in other chlorocarbon media) than in benzene, and botli are better than heptane. In connection with this latter point, Ugelstad and coworkers have studied the reactions of quaternary ammonium phenoxide ions with alkyl halides in a variety of media and concluded that the... 

The rate of reaction of phosphorus oxychloride with phenols to produce triaryl phosphates is increased by the addition of quaternary ammonium salts and the reaction temperature can be reduced without loss of overall yield [1,2]. The analogous reaction between phenoxide anions and thiophosphoryl chloride produces aryl phosphoro-dichloridothoates [3]. As with the acylation of enolizable (3-dicarbonyl compounds (3.3.12), phosphorylation leads to the predominant formation of the E-O-phos-phoryiated derivatives [4,5]. 

Because of the differential partitioning of hydroxide and phenoxide anions into organic solvents by quaternary ammonium cations, the catalysts generally have little effect on the Reimer-Tiemann reaction of phenols with dihalocarbenes [15]. Cetyltrimethylammonium bromide has been used in the two-phase dichloromethyl-ation of polysubstituted phenols (Scheme 7.21, Table 7.10) under Makosza s conditions [16,17] ring expansion of the reaction products provides an effective route to tropones. The rate of the reaction is enhanced by ultrasonic radiation [16]. 

A slow non-competing liquid/liquid reaction with no catalyst present gave only 78 % O-alkylation. Thus the active site of the lipophilic phosphonium ion catalysts appears to be aprotic, just as in analogous phase transfer catalyzed alkylations with soluble quaternary ammonium salts 60), Regen 78) argued that the onium ion sites of both the 17% and the 52% RS tri-n-butylphosphonium ion catalysts 1 are hydrated, on the basis of measurements of water contents of the resins in chloride form. Mon-tanari has reported measurements that showed only 3.0-3.8 mols of water per chloride ion in similar 25 % RS catalysts 74). He argued that such small hydration levels do not constitute an aqueous environment for the displacement reactions. No measurements of the water content of catalysts containing phenoxide or 2-naphthoxide ions have been reported. 

Sodium thiophenoxide appears to be the best reagent for the selective demethyla-tion of quaternary ammonium salts." 2-Butanone is used as solvent. The reaction involves Sn2 attack by the phenoxide anion on the N-methyl group. An example is the demethylation of ( )-laudanosine methochloride to laudanosine. A limitation... 

Recently, the groups of Mukaiyama [69] and Feng [70] independently demonstrated that aryl oxide anions such as phenoxide [69] or binaphthoxide [70] can be used instead of fluoride to activate (TMS)CF3 as a Lewis base. Several types of aromatic ketones and aldehydes were smoothly trifluoromethylated within a few hours in the presence of cinchona-based quaternary ammonium salts bearing an aryl oxide anion 148 or 149, affording the corresponding product in excellent yields and with moderate to high ee values (up to 87% ee) (Schemes 8.58 and 8.59). 

Yang and Wu [201] investigated the esterification of dipotassium phthalate with benzyl bromide in a solid-liquid system. We found that the catalytic intermediate, formed by the solid reactant with tetrabutylammonium bromide, was the key-reacting component in SLPTC. Yang and Wu [202] explored the kinetics of the O-allylation of sodium phen-oxide with allyl bromide in the presence of quaternary ammonium salt catalyst in a solid-liquid system. The behaviors of the catalytic intermediate tetrabutylammonium phenox-ide, formed from the reaction of solid sodium phenoxide and tetrabutylammonium bromide in the solid-liquid phases, are important in conducting the etherification, and pseudo-first-order kinetics are observed. 

Polyethylene glycols (PEGs) can also be used as the catalyst in SLPTC. Chu [207] reported the kinetics for etherification of sodium phenoxide with benzyl bromide using quaternary ammonium salts and PEG as the catalyst in SLPTC. When PEG is used as the catalyst, formation of the complex PEG-Na PhO mainly occurs at the solid-liquid interface. The phenoxide anion carried by PEG can dissolve much more than its original... 

The role of bromide in DPC catalysis is still unclear. It was suggested that NR Br works as a base to ionize phenol to phenoxide anion [51] or as a surfactant to stabilize Pd(0) nanoparticles [65]. However, no other bases or surfactants have even come close to its activity in DPC synthesis. Quaternary ammonium and phosphonium bromides are expensive and difficult to recover in downstream processing and, therefore, have a substantial impact on the DPC cost structure. For the process economics, it was critical to replace these compounds with less expensive equivalents, which could be done by two ways either replacing QBrs with inexpensive NaBr or nonbromide nonquaternary salts. 

Laurtrimonium trichlorophenoxide Synonyms Dodecanaminium, N,N,N-trimethyl, salt with 2,4,5-trichlorophenol Lauryl trimethyl ammonium 2,4,5-trichloro phenoxide Classification Quaternary ammonium compd. Empirical C15H35N C6H2CI3O Uses Antimicrobial, antistat in cosmetics... 

Catechols likewise undergo 0-alkylation under phase transfer conditions, yielding methylenedioxy derivatives on reaction with methylene bromide [8]. This reaction constitutes a useful route to this commonly occurring oxygen heterocycle as well as providing a facile protection method for 1,2-dihydroxyarenes. Dibromo-methane rather than the more reactive diiodomethane was used in this reaction because the latter is a source of iodide ion which poisons the phase transfer catalyst by selectively ion-pairing with the quaternary ammonium cation. Phenoxide ion can apparently compete successfully with bromide but not iodide in the formation of an extractable ion pair under these conditions. 

Phenols have been phosphorylated under phase transfer conditions in the presence of a nucleophilic catalyst [31, 32]. The reaction of 4-nitrophenol with dimeth-oxythiophosphoryl chloride is ordinarily slow and leads to a mixture of the desired methyl parathion and hydrolysis products. Addition of N-methylimidazole enhanced the rate but the best results were obtained when both the imidazole and a quaternary ammonium salt (TBAB) were used at the same time. The co-catalysis was accounted for in terms of nucleophilic activation of the acylating agent by imidazole and solubilization of the phenoxide by ion pairing with the quaternary ion. The overall transformation is formulated in equation 6.13. 

Schnell and coworkers employed tertiary amines and quaternary ammonium compounds to improve the synthesis of polycarbonates and the monomer, diphenyl carbonate. Schnell and Bottenbruch proposed that the tertiary amines formed adducts with the acid chloride in the organic phase forming a more reactive intermediate iV). This is possible, but it is more likely that they are phase transfer agents for the phenoxide. 

Displacement of a tertiary amine by the attack of a nucleophile on the a-carbon of a quaternary salt is a reaction that competes with the Hofmann elimination and is found to take place preferably with weak bases (carbonate, acetate, etc.) . In some cases steric influences rather than basicity may promote the substitution reaction in favor of elimination. For example, the reaction of propyltrimethyl-ammonium ion with hydroxide ion yields 19% methanol and 81% propylene, whereas the reaction with phenoxide ion yields 65% anisole and 15% propylene (equation 13) . Phenyl groups attached... 

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