胶团噻唑衍生物对安息香不对称合成反应的催化作用

通过α-(1-萘基)-N-硫代甲酰乙胺与卤代酮反应制得六个光学活性的4-烷基-3-α-(1-萘基)乙基噻唑溴化物烷基碳链长=1,2,7.11,15,21). 将其用于催化水溶液中的安息香缩合反应, 所得产物收率约20-30%具有较高的光学纯度(47-57%). 在各种缓冲溶液中测定了S(+)-4-甲基-3-α-(1-萘基)乙基噻唑氯化物(Ta)的胶团性质和由它催化的不对称安息香缩合反应. 临界胶团浓度(cmc)证明(Ta)在反应中确以胶团形式催化. 在硼砂溶液中, 安息香的收率高达61%, 光学纯度23.6%.     

Artificial enzymes with thiazolium and imidazolium coenzyme mimics

Hydrophobic thiazolium and imidazolium coenzyme mimics in the presence of modified-polyethylenimine enzyme mimics catalyze the benzoin condensation 2300-3300 times faster than the coenzyme mimics alone. Polycationic enzyme mimics provide not only a hydrophobic binding domain for coenzyme and substrate, but also electrostatic stabilization of anionic species that arise along the reaction pathway of the benzoin condensation.     

Thermal analysis of boron complexes containing ligands of the type R-C(CH2OH)3

The thermal behaviours of certain salts of the complex “ethriol-” and “methriolboric” acids have been investigated by means of Derivatograph and IR spectra. It is shown that compounds of this type decompose in three main stages on heating: 1) the crystallization water is lost, 2) the condensation water is lost and dimers are formed containing bridge bonds B₄-O-B₄; 3) up to 600–700? all the organic matter is lost; the residue is the corresponding borate (1 ∶ 1). The possibility of performing a fast full analysis by means of the TG and DTG curves has been demonstrated.     

Application of polymer-bound thiazolium salts to the synthesis of acyloins and benzoins: Effects of solvent and substituents of the thiazolium nucleus

Covalent immobilization of the thiazole nucleus on a chloromethylated polystyrene copolymer results in the formation of a catalytically active thiazolium salt, capable of repeated acyloin and benzoin condensations. The nature of the solvent and the substituents on the thiazolium nucleus has been found to have marked effects of the rate of catalysis.     

A γ-cyclodextrin thiazolium salt holoenzyme mimic for the benzoin condensation

Several thiazolium salts have been attached to a C-6 carbon of γ-cyclodextrin. They catalyze the benzoin condensation of benzaldehyde very effectively.     

Acyloin condensation in aqueous system by durable polymer-supported thiazolium salt catalysts

We characterized three low-molecular-weight thiazolium salt analogues: N-methyl-5-(2′-benzyloxyethyl)-4-methylthiazolium iodide (MBMTI), N-methyl-4-phenylthiazolium iodide (MPTI), and N-methylbenzothiazolium iodide (MBTI). MBMTI, having high-electron density on the thiezolium ring, was found to be a durable thiazolium salt in buffer solution. Then, the polymer-supported thiazolium salt catalyst having MBMTI structure as a catalytic site for acyloin condensation was prepared by the polymerization of the corresponding thiazole monomer and the following quaternization. The polymer catalyst had excellent catalytic activity even in buffer solution, while the corresponding low molecular weight catalyst did not show any activity in aqueous system. Furthermore, the durable polymer catalyst could be reused under the aqueous condition. © 1994 John Wiley & Sons, Inc.     

Catalytic conjugate additions of carbonyl anions under neutral aqueous conditions

The conjugate addition of carbonyl anions catalyzed by thiazolium salts that is fully operative under neutral aqueous conditions has been accomplished. The combination of alpha-keto carboxylates and thiazolium-derived zwitterions produces reactive carbonyl anions in a buffered protic environment that readily undergo conjugate additions to substituted alpha,beta-unsaturated 2-acyl imidazoles. The scope of the reaction has been examined and found to accommodate various alpha-keto carboxylates and beta-aryl substituted unsaturated 2-acyl imidazoles. The optimal precatalyst for this process is the commercially available thiazolium salt 5, a simple analogue of thiamin diphosphate. In this process, no benzoin products from carbonyl anion dimerization are observed. The corresponding 1,4-dicarbonyl compounds can be efficiently converted into esters and amides by way of activation of the N-methylimidazole ring via alkylation.     

The “formoin reaction” : A promising entry to carbohydrates from formaldehyde

Formaldehyde condensation catalyzed by the conjugate bases of thiazolium ions, leads to a complex mixture (“formoin mixture”) of unbranched aldoses and ketoses, in which glucose, galactose, glyceraldehyde dimer, xylose and arabinose have been identified.     

Azolium and acetate ions in DMF: Formation of free N-heterocyclic carbene. A voltammetric analysis

In order to reveal the possible formation of free N-heterocyclic carbene (NHC) in DMF-azolium and acetate solutions, the proton exchange equilibrium between azolium cations and CH₃COO⁻ was investigated (by cyclic voltammetry) by adding CH₃COOH or tetrabutylammonium acetate to DMF solutions of imidazolium or thiazolium salts of different acidity.The voltammetric analysis confirms that the deprotonation of the azolium cation by CH₃COO⁻ (with the formation of free NHC) is significant in the case of the more acidic thiazolium cations, while it is not effective with the less acidic imidazolium ones.Accordingly, the NHC-catalyzed benzoin condensation was carried out in DMF solutions of azolium salts, tetrabutylammonium acetate, and benzaldehyde. Benzoin was isolated only starting from the more acidic thiazolium salts.     

Formation of chiral ionic liquids and imidazol-2-ylidene metal complexes from the proteinogenic aminoacid l-histidine

Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(n-propyl)₂-OMe⁺Br⁻]. It features a melting point of 39 °C and may serve as a useful readily available optically active ionic liquid. Its subsequent treatment with silver oxide gave the corresponding l-histidine derived chiral N-heterocyclic carbene complex [“(carbene)₂Ag · AgBr₂”]. Transmetallation by treatment with Pd(CH₃CN)₂Cl₂ or [Rh(cod)Cl]₂ led to the formation of the respective chiral late metal imidazol-2-ylidene complexes [“(carbene)₂PdCl₂”] and [“(carbene)RhCl(cod)”], respectively. Four diastereomers of the square planar palladium system were observed. Due to the additional chirality center in the l-histidine-derived “Arduengo-carbene ligand” two diastereomers of the rhodium carbene complex were formed.     

103Rh and 33s hyperfine interactions in tetraphenylarsonium-bis ( maleonitriledithiolato ) rhodate (II), (Ph4As)2[Rh(mnt)2]: a single-crystal EPR-ENDOR study

The complete ¹⁰³Rh and ³³S hyperfine coupling tensors of the 4d⁷ low-spin chelate tetraphenylarsoniumbis (maleonitriledithiolato)rhodate(II) doped into the corresponding nickel complex salt have been measured by EPR-ENDOR spectroscopy. Both interactions are small and confirm that the unpaired electron is in an “out-of-plane” π-type molecular orbital. The Rh-S bonds are less covalent than bonds in the isoelectronic Pd(III) complex.     

Catalytic intramolecular crossed aldehyde--ketone benzoin reactions: a novel synthesis of functionalized preanthraquinones

Stereochemically and functionally rich polycyclic compounds are obtained by the first crossed aldehyde-ketone benzoin reaction in excellent yield under mild reaction conditions (5-20 mol % thiazolium salt, 10-70 mol % DBU, tBuOH, 40 degrees C, 30 min). This novel catalytic methodology offers a convenient approach to sophisticated molecular architectures useful for the stereocontrolled construction of polycyclic compounds as well as the fully regiocontrolled synthesis of anthra- and naphthoquinones.     

N-Heterocyclic carbene catalyzed intramolecular crossed aldehyde-ketone benzoin condensation in the chalcone of o-phthalaldehyde: a facile synthesis of naphthalenones

The intramolecular crossed aldehyde-ketone benzoin condensation in the chalcone of o-phthalaldehyde (OPA) catalyzed by N-heterocyclic carbene (NHCs) generated in situ from readily available imidazolium and thiazolium salts is described. In this reaction, bicyclic α-hydroxyl ketones (naphthalenone type tertiary alcohol) were selectively produced in good yields (75-94%) in shorter reaction times (20 min) through nucleophilic addition of acyl anion generated by umpolung in OPA-chalcone (regio controlled).     

Side products in the rosenmund reduction of benzofuran-2-carboxylic acid chlorides

The corresponding 1,2-bis(2-benzofuryl)ethylenes and 2-methylbenzofurans were isolated as side products, along with the principal reaction products (2-formylbenzo-furans), in the Rosenmund reduction of 3-, 5-, and 7-alkylbenzofuran-2-carboxylic acid chlorides. The bis(2-benzofuryl)ethylene structure was confirmed by the IR and PMR spectra data and alternative synthesis by reduction of the corresponding benzofuroins, obtained by benzoin condensation of 2-formylbenzofurans, with zinc amalgam in acidic media. The side formation of desoxybenzofuroin derivatives was noted in some cases in the benzoin condensation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 744–748, June, 1977.     

Chiral, bridged bis(imidazolin-2-ylidene) complexes of palladium

Varieties of chiral, bridged bisimidazolium salts as well as the synthesis of palladium complexes of general formula with the corresponding chelating N-heterocyclic carbene ligands is reported. This is the first systematic study of chiral bis(imidazolin-2-ylidene)palladium(II) complexes bearing chiral groups on the endocyclic nitrogens. Structural proof of such a chiral palladium(II) complex is presented by way of an X-ray diffraction study of complex 3a.     

吡啶氮桥联双环三唑鎓盐的合成及其在催化苯偶姻缩合、酯交换反应中的应用

合成了12个吡啶氮桥联的双环三唑鎓盐2a～2l卡宾催化剂前体,用于催化苯偶姻缩合反应和酯交换反应,考察了反应条件对催化反应的影响,并与其它三唑鎓盐的催化活性进行了比较.结果表明,在较低催化剂用量下,催化剂2c表现出优良的催化活性,分离产率最高分别达到98%和93%.     

Syntheses of new thiazolium salt polymers and their catalytic activities

Thiazolium salt polymers were synthesized for the purpose of obtaining a more efficient catalyst for the acyloin condensation. A new thiazolium salt, N-methyl-4-vinylphenylthiazolium iodide was synthesized. However, this compound did not homopolymerize by radical initiator. Therefore, 4-vinylphenylthiazole was polymerized and the obtained polythiazole was quarternized by methyl iodide. Poly(N-methyl-4-vinylphenylthiazolium iodide) was examined as a polymer-catalyst for the acyloin condensation of several aldehydes. This polythiazolium salt had an excellent catalytic activity in organic solvents, even in nonpolar solvents. Moreover, it was observed that the catalytic activity increases with the decrease of quarternization.     

Asymmetric benzoin condensation catalyzed by chiral rotaxanes tethering a thiazolium salt moiety via the cooperation of the component: can rotaxane be an effective reaction field?

Although some reactions on rotaxanes have been reported, the characteristic features of the rotaxanes providing unique reaction fields have hardly been studied, especially as catalyst. In our continuous studies on interlocked molecules such as rotaxanes and catenanes, we have noticed the importance of such interlocked structures with high freedom in functionalized materials such as molecular catalyst. For catalytic asymmetric benzoin condensations, two optically active rotaxanes possessing thiazolium salt moieties were prepared using the binaphthyl group as the chiral auxiliary. The benzoin condensations of aromatic aldehydes catalyzed by the chiral rotaxanes as catalysts gave optically active benzoins with ca. 30% ee in moderate to high chemical yields depending upon the structure of rotaxane and the reaction conditions employed. From the results, two intrarotaxane chirality transfers are confirmed: (i) through-space chirality transfer from wheel to axle and (ii) through-bond chirality transfer controlled with an achiral wheel. Because these asymmetric reaction fields are specific to the rotaxane structure, the importance and possibility of the "rotaxane field" as a particular reaction field is demonstrated in this work.     

Abnormal oxazol-4-ylidene and thiazol-4-ylidene rhodium complexes: synthesis, structure, and properties

A series of new 2,3,5-triaryl-substituted oxazolium and thiazolium salts are readily prepared by a Tf(2)O-mediated intramolecular cyclisation and their use as precursors for the synthesis of novel oxazol-4-ylidene and thiazol-4-ylidene rhodium complexes has been developed.     

Nickel complexes of a bis(benzimidazolin-2-ylidene)pyridine pincer ligand with four- and five-coordinate geometries

The four- and five-coordinate complexes [(CNC)NiX(2)] (X = Cl, Br, I), [(CNC)NiX]PF(6) (X = Cl, Br) and [(CNC)NiCl]Cl·H(2)O have been isolated, where CNC is the bis(N-butylbenzimidazolin-2-ylidene)-2,6-pyridine pincer ligand. A five-coordinate geometry is rare for this class of complex. Where amenable, the complexes have been structurally characterised by single crystal X-ray diffraction studies and in solution by NMR, UV-vis and MS studies. The five-coordinate dibromo complex [(CNC)NiBr(2)] is readily prepared on the gram-scale from the benzimidazolium salt precursor and Ni(OAc)(2)·4H(2)O in DMSO without the exclusion of air. Halide exchange and salt metathesis reactions using [(CNC)NiBr(2)] afford the other four- and five-coordinate complexes. [(CNC)NiBr(2)] displays very low solubility, and upon dissolution affords solutions of the four-coordinate [(CNC)NiBr](+). Factors that influence the formation of four- or five-coordinate complexes with this ligand class are discussed.