Synthesis of Benzyl Esters of Glycyrrhizic Acid in the Presence of Phase-Transfer Catalysts

Benzyl esters of glycyrrhizic acid were synthesized using PhCH₂Br in DMSO-CH₂Cl₂-NaOH in the presence of phase-transfer catalysts, such as tetraalkylammonium salts and 2-methyl-2-propanol.     

Synthesis of New Phase-Transfer Catalysts and Their Application in Asymmetric Alkylation

Despite phase transfer catalysis (PTC) is an important and useful method in organic synthesis, asymmetric synthesis using chiral phase-transfer catalyst has not been well documented and limited number of chiral phase-transfer catalyst have been developed^[1].In 1989,O'Donnell published his pioneering work in the asymmetric synthesis of α-amino acids by enantioselective alkylation of a prochiral protected glycine derivative using chiral phase-transfer catalyst^[2]. Since then, several groups reported their improvements on enantioselectivity and applicability on this useful synthetic reaction^[3,4]. However, almost all of the chiral phase-transfer catalysts reported so far are the derivatives of cinchona^[5]. In this presentation, we wish to describe the design and synthesis of a new type of chiral phase-transfer catalyst based on the camphor and its application in asymmetric alkylation of tert-bntyl glycinate-benzophenone Schiff base.     

Asymmetric Phase-Transfer Catalysis

Both in the laboratory and industrially , phase-transfer catalysis offers the potential to induce asymmetry into reactions with anionic intermediates. Equation (a) provides an example (conditions: a) 10 mol % phase-transfer catalyst, BnBr, CsOH⋅H₂O, PhMe, 15–24 h, −78°C).     

Chiral quaternary phosphonium salts: a new class of organocatalysts

Phase-transfer catalysis has widely been used as a prime synthetic tool for both laboratory and industrial processes. During the last twenty years, asymmetric phase-transfer catalysis using chiral organocatalysts has attracted widespread interest. However, the scope of chiral phase-transfer catalysis has been limited mostly to the quaternary ammonium salts. As an emerging area, the recent developments in the application of quaternary phosphonium salts as chiral phase-transfer catalysts are discussed in this article.     

Mechanism of Dehydrobromination of 1,2-Dibromo-1-phenylethane under Conditions of Phase-Transfer Catalysis

Selective dehydrobromination of 1,2-dibromo-1-phenylethane to -bromostyrene was effected under conditions of phase-transfer catalysis in systems containing KOH, toluene, and tetraalkylammonium bromides. The high selectivity of the catalytic systems originates from stabilization by lipophilic cation of the phase-transfer catalyst of a E1cb-like transition state in the E2 mechanism. In the presence of a catalytic amount of lipophilic alcohols, phenylacetylene was obtained. Substrate activation by alcohol molecules is explained by enhancement of the acceptor power of halogen atoms due to solvation and by increased mobility of hydrogen atoms.     

相转移催化法实现聚苯乙烯的功能化转变

以对羟基苯甲醛的钠盐为亲核取代试剂,采用相转移催化进行了大分子氯甲基聚苯乙烯的亲核取代反应,将其转变为侧链带有功能性基团醛基的聚苯乙烯;考察了反应条件(如有机溶剂的极性、催化剂种类及用量、有机相与水相之比等)对大分子相转移催化反应的影响,并根据相转移催化反应机理与相关的动力学规律进行了分析.结果表明,通过相转移催化亲核取代反应,可将氯甲基聚苯乙烯大分子链上的氯原子转化,制得侧链带有醛基的聚苯乙烯;溶剂的极性越强,负离子的反应活性也越高;催化剂季铵正离子的亲脂性越强,相转移催化反应的速率越快.当催化剂浓度较低时,四丁基溴化铵比十六烷基溴化铵的催化效果好;当催化剂浓度较高时,十六烷基溴化铵比四丁基溴化铵的催化效果好.另外,有机相与水相之比对相转移催化反应有较大的影响.     

Kinetics of synthesizing liquid-crystals, 4, 4"-dialkoxybiphenyl by phase transfer catalysis

Reactions of 4,4"-biphenol and bromoalkanes to synthesize 4,4"-dialkoxybiphenyls were carried out under phase-transfer catalysis. Quaternary ammonium salts (QBr) and propansultan (QSO₃) were used as the phase transfer catalysts. Eight liquid crystals including symmetric and asymmetric diethers and the active catalyst (QO(Ph)₂OQ) were produced from the reactions.     

Synthesis of 4-Substituted Bisnaphthalimides

The synthetic route to 4-substituted bisnaphthalimides consisting in reaction of 4-halonaphthalic anhydrides with a,w-diaminoalkanes followed by halogen substitution with dialkylamino group is more promising than imidating coupling of 4-dialkylaminonaphthalic anhydrides for it opens wider synthetic opportunities and ensures better yields of target products. Dihalosubstituted bis-naphthalimides can be prepared by N-alkylation of the corresponding naphthalimides with polymethylene dibromides under conditions of phase-transfer catalysis in the presence of tetraalkylammonium salts.     

Recent Progress in Asymmetric Ion-Pairing Catalysis with Ammonium Salts

Quaternary ammonium salts play an important role in asymmetric catalysis. In this Minireview, how asymmetric ion-pairing catalysis with ammonium ions has been utilized in organic synthesis is explained, particularly in the design of novel catalytic cycles. This includes the use of chiral ammonium-based catalysts for the construction of challenging stereogenic centers. Ammonium-derived electrophilic reagents, typically formed in situ and in the context of phase-transfer catalysis (PTC), have also been utilized in asymmetric bond-forming reactions. Furthermore, ammonium salts have been employed as substrates in several stereocontrolled C−N bond cleavage processes, leading to enantioenriched products by using novel asymmetric induction modes. In addition, merging ammonium ion-pairing catalysis with other catalytic approaches has also emerged as a new platform for achieving previously less straightforward reactions, thereby allowing new synthetic applications.     

N-Alkylation of Phenobarbital Under Phase-Transfer Catalysis Conditions

This communication describes a convenient procedure for the preparation of alkylated derivatives of phenobarbital using phase-transfer catalysis without solvent conditions.     

Recent advances in asymmetric phase-transfer catalysis

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. This concept, together with the synthetic versatility of phase-transfer catalysis, provides a reliable and general strategy for the practical asymmetric synthesis of highly valuable organic compounds.     

温控相转移纳米铑催化高碳烯烃氢甲酰化反应

 基于温控配体 Ph₂P(CH₂CH₂O)₁₆CH₃ 稳定的 Rh 纳米催化剂在水/1-丁醇两相体系中具有温控相转移功能, 将其用于高碳烯烃氢甲酰化反应中. 在优化的反应条件下, 1-辛烯转化率和醛收率分别达 98% 和 96%, 对其它高碳烯烃氢甲酰化反应也具有较高的催化性能. 催化剂和产物通过简单的相分离即可分开, 连续使用 3 次后, 催化剂性能未见明显降低.     

含松香骨架的新型手性季铵盐相转移催化剂的合成及其在不对称环氧化反应中的应用

以天然松香为原料合成了4个新型手性季铵盐类相转移催化剂, 并用于催化不对称查尔酮环氧化反应, 发现这类手性相转移催化剂可以有效地催化查尔酮的不对称环氧化, 环氧化产物ee最高达20%.     

基于天然氨基酸的双环手性季铵盐相转移催化剂的合成及催化性能研究

以L－脯氨酸及L－羟基脯氨酸为原料合成了4个新型手性季铵盐磁相转移催化 剂，并用于催化不对称查耳酮环氧化反应，高产率得到相应环氧化合物，ee最高达 9％。     

Phase-transfer catalyst-induced changes in the absorption and fluorescence behavior of some electron donor-acceptor molecules.

The quaternary ammonium salts find extensive use in a variety of chemical applications as surfactants and phase-transfer catalysts. Even though the interaction of the surfactants with various systems has been studied rather extensively, very little information is available on how the phase-transfer catalysts (PTC) interact with the dipolar systems in nonpolar media and how/whether these solubilizing agents affect the properties of the dissolved molecules. In this paper, the interaction of several tetraalkylammonium salts, commonly used as PTC, with a number of electron donor-acceptor (EDA) systems has been studied by absorption and fluorescence spectroscopy. The phase-transfer catalysts have been found to affect both the absorption and fluorescence properties of the EDA systems. The spectral changes of the EDA molecules induced by the tetraalkylammonium salts suggest the formation of an 1:1 complex between the two in nonpolar media. An electrostatic interaction between the phase-transfer catalysts (which exist as ion pairs in nonpolar media) and the dipolar molecules is shown to be the driving force for the formation of the complex. The dependence of the formation constant of the complex on the polarity of the media suggests a charge-transfer nature of the complex. It is shown that the anionic component of the salts serves as a source of electron to the positive end of the dipolar molecule, while the tetraalkylammonium cation, besides helping solubilization of its anionic counterpart in the nonpolar media, serves neutralizing the negative charge at the acceptor end of the EDA molecule. In effect, a cooperative influence of the cationic and anionic components of the PTC enhances the charge separation within the dipolar fluorophores. On the basis of the PTC-induced changes in the photophysical behavior of the EDA molecules, a possible structure for the 1:1 complex has been proposed. It has been concluded that a phase-transfer catalyst should not be treated as an innocuous substance that merely helps transfer of a polar substance from a polar to a nonpolar environment. Instead, it is demonstrated that the association of a PTC with a dipolar species can significantly change various properties of the latter.     

Enantioselective Mannich reaction of γ-malonate-substituted α,β-unsaturated esters with N-Boc imines catalyzed by chiral bifunctional thiourea-phosphonium salts

A novel enantioselective Mannich reaction of γ-malonate-substituted α, β-unsaturated esters with N-protected arylaldimines was realized by using asymmetric phase-transfer catalysis (APTC). With amino acid-derived bifunctional thiourea-phosphonium salts as a catalyst, a series of enantio-enriched Mannich products could be synthesized under very mild and simple reaction conditions with high yields and enantioselectivities.     

Comparative study of chemically immobilized and conventional homogeneous ionic liquids as phase-transfer catalysts for the N-alkylation of heterocyclic compounds

Various ionic liquids (ILs) were screened for their phase-transfer catalytic (PTC) activity using the N-alkylation of nitrogen heterocycles as the model reaction. Immobilized ILs behaved extremely well and proved to be far better catalysts than conventional homogeneous PTCs in terms of their stability, easy recovery, and reusability. The investigation also demonstrated that quaternary tetraalkylammonium salts offer very high catalytic activity, whereas aromatic heterocyclic tetravalent nitrogen catalysts (imidazolium- and pyridinium-based salts) were poorly active.     

Electrochemical Study of Phase-Transfer Catalysis Reactions: The Williamson ether synthesis

The transfer properties of the ionic species involved in the Williamson ether synthesis by phase-transfer catalysis were investigated using electrochemical techniques developed for the study of polarised liquid/liquid interfaces. This approach allows the measurement of the apparent partition coefficients of the transferring species. From these data, it is proposed that the role of the phase-transfer catalyst salt in the reaction mechanism is to establish a Galvani distribution potential difference between the two phases which in turn acts as the driving force for transferring the reactive aqueous ions to the organic phase.     

Tetraalkylammonium Salts as Hydrogen‐Bonding Catalysts

Although the hydrogen‐bonding ability of the α hydrogen atoms on tetraalkylammonium salts is often discussed with respect to phase‐transfer catalysts, catalysis that utilizes the hydrogen‐bond‐donor properties of tetraalkylammonium salts remains unknown. Herein, we demonstrate hydrogen‐bonding catalysis with newly designed tetraalkylammonium salt catalysts in Mannich‐type reactions. The structure and the hydrogen‐bonding ability of the new ammonium salts were investigated by X‐ray diffraction analysis and NMR titration studies.     

Phase-Transfer catalyzed free-radical polymerization of acrylonitrile

The kinetics of phase-transfer catalyzed free-radical polymerization of acrylonitrile (AN) was carried out with water-soluble initiator peroxomonosulphate (PMS) with phase-transfer catalysts (tetrabutylammonium chloride and benzyltributylammonium chloride (TBAC and BTBAC) in tolune/water two-phase systems in the temperature range of 45–55°C at fixed pH (4) and ionic strength. The rates of polymerization (R_p) were evaluated at various values of [PMS], [PTC], and [AN]. It has been observed that the rates of polymerization increase with an increase of [AN], [PMS], and [PTC]. A kinetic scheme has been proposed to account for the experimental observations. © 1994 John Wiley & Sons, Inc.