Facile synthesis of methylthiomethyl esters through Pummerer-type rearrangement of carboxylic acids and DMSO under metal-free conditions

A green and cost-effective Pummerer-type rearrangement between readily accessible carboxylic acids and DMSO has been achieved under metal-free conditions in satisfactory to excellent yields. The transformation for the synthesis of valuable methylthiomethyl esters is shown to be a convenient strategy for various (hetero)aromatic acids, α,β-unsaturated carboxylic acids and saturated alkyl carboxylic acids with good functional group tolerance.     

Direct synthesis of novel amphiphilic cyclodextrin

A novel amphiphilic cyclodextrin derivative was obtained by controlled esterification of lauric acid chloride on the primary face of the native β-cyclodextrin in a one step synthesis. The characterization of the substitution degree and isomer structure was performed by mass and NMR spectroscopies. A specific purification procedure by sublimation was developed in order to eliminate the excess of lauric acid molecules in the reaction product. The sublimation efficiency was assessed by differential scanning calorimetry (DSC) in quantifying the remaining fatty acid. In this way the duration of the sublimation process could be optimized.     

Advances in the catalyses of polymerizations

Abstract

Nearly all technical processes for the production of polymers are carried out in the presence of catalysts. In the case of addition polymerization reactions, two mechanisms are possible: Start of the reaction via an initiator (e.g., peroxides) or start via a true catalyst (e.g., Ziegler/ Natta systems). In both areas remarkable progress has been made: Cationic “living” polymerizations of oxacycloalkanes, group transfer polymerization, metal-catalyzed alternating copolymerization of ethylene with carbon monoxide, and metallocene-catalyzed polymerizations of alpha-olefins. The polymerization of alpha-olefins with metallocene catalysts not only leads to the improvement of well-known polymers like polyethylene and polypropylene, but also enables the production of new polymers like syndiotactic polypropylene, syndiotactic polystyrene, and cycloolefin copolymers on an industrial scale.     

Effects of cyclodextrin on hydrolysis and the Smiles rearrangement of salicylic acid esters

The effect of -cyclodextrin (-CD) on aqueous hydrolysis of methyl,p-, andm-nitrophenyl salicylates as well as on the Smiles rearrangement ofp-nitrophenyl salicylate was studied. No effect of -CD on the pH-independent rate constant of aqueous hydrolysis of methyl ester was observed, while -CD accelerated aqueous hydrolysis of nitrophenyl esters byca. 10 times. The inclusion of these esters into the cavity of -CD is accompanied by a change in the mechanism of hydrolysis: free ester in the deprotonated form undergoes hydrolysis through the mechanism of intramolecular general base catalysis, while the ester bound to cyclodextrin is hydrolyzed due to the nucleophilic attack of the deprotonated hydroxyl group of -CD at a neutral substrate molecule. The effects of cyclodextrin on the rate constant of borate-catalyzed hydrolysis were interpreted by assuming that the substrate bound to -CD undergoes borate-assisted attack at the deprotonated cyclodextrin hydroxyl group. The Smiles rearrangement, which is an intramolecular nucleophilic substitution reaction, is accelerated in the presence of -CD.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2658–2665, November, 1996.     

Hydrolysis of phosphate esters with polymer-supported catalysts containing cyclodextrin pendant group

Polymer-supported catalysts of several kinds, including-cyclodextrin (P-CD),-cyclodextrin-diethylenetriamine (P-CD-DETA), and-cyclodextrin-N-methylhydroxamate (P-CD-NMHA)-containing polymers, as well as their corresponding metal complexes, were synthesized and examined as catalysts for the hydrolysis of phosphate esters. The kinetic measurements were performed in a phosphate buffer (0.05 M, pH 8.2) at a temperature of 25.0±0.1 °C. Each kinetic run was initiated on introducing ester stock solution (0.13 ml) containing diphenylp-nitrophenyl phosphate (DPPNPP) in dioxane (0.010 M). The rate of hydrolysis of DPPNPP was evaluated by measuring the absorbance of liberatedp-nitrophenol at 402 nm. The dissociation constants between DPPNPP and the polymers P-CD, P-CD-DETA and P-CD-NMHA obtained from Eadie-type plots were 16.8, 16.4 and 8.0 (×10^–3 M) and the acceleration factors were 1.5, 2.8 and 8.6 respectively. Hence P-CD-NMHA is the most promising catalyst. The activation parameters, preexponential factor (A) and activation energy using P-CD-NMHA as catalyst, areA=1.2×10⁹ min^–1 andE _a=43 kJ/mol respectively; the latter was about 12 kJ/mol lower than the activation energy of spontaneous hydrolysis. The results indicate that the catalytic power of P-CD-NMHA may reflect the combined behavior of molecular recognition and nucleophilicity.     

Alternative esters in the synthesis of ZD0947

Alternatives to the original iso-borneol and allyl esters were investigated in the synthesis of ZD0947 (1). Homologous allylic esters were prepared in higher yields and were more readily purified than for the existing route, but offered no further benefits later in the synthesis. However, the PNB-substituted ester series provided crystalline intermediates, higher yields and simplified isolations through-out, and utilised a heterogeneous hydrogenation, thus reducing the residual catalyst levels.     

PTSA-catalyzed one-pot synthesis of quinoxalines using DMSO as the oxidant

An efficient p-toluene sulfonic acid–catalyzed, one-pot, two-step oxidative system for cyclization of o-diaminobenzene with 1,2-diaryl-2-hydroxyethanone to quinoxalines was described. A nontoxic, readily available oxidant, dimethylsulfoxide (DMSO), was applied in this process. A broad range of substrates was applied to this method, and target compounds were obtained with good yields.     

α-酮酸酯的合成研究进展

α-酮酸及其酯是一类双官能团化合物, 性质活泼而特殊, 是重要的有机合成、药物合成及生物合成中间体。文中扼要论述了近二十年来α-酮酸酯的合成研究进展。     

Diastereoselective synthesis of aziridine esters via amino selanyl esters

A synthesis of aziridine esters based on the cyclisation of amino selanyl esters induced by the selanyl group activation was developed with either the Meerwein salt or NBS. Two asymmetric approaches are proposed: the diastereoselective reductions of α-selanyl β-iminoesters derived from α-oxoesters, which lead to cis chiral aziridine esters 6 and 6′; and the diastereoselective conjugate additions of a chiral amide to α,β-unsaturated esters providing trans chiral aziridine esters 6 and 6″.     

Preparative synthesis of veratraldehydeoxime esters

Preparative syntheses of veratraldehydeoxime esters 6–24, available fragrances produced from vanillin (1), in 82–92% yield from veratraldehydeoxime (3) were developed. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 558–560, November–December, 2008.     

Application of palladium catalyses to a simple synthesis of (±)-pyrethrolone

By sequential application of three palladium catalyzed reactions, namely, palladium catalyzed telomerization of butadiene with phenol, oxidation of terminal olefin of the telomer to methyl ketone, and palladium catalyzed elimination of phenol, an E and Z mixture of 5,7-octadien-2-one was prepared in a high yield. This compound was converted to an E and Z mixture of pyrethrolone. The Z form of pyrethrolone was separated from the E isomer by selective adduct formation of the latter with tetracyanoethylene.     

Thermodynamic origin of the increased rate of hydrolysis of phosphate and phosphorothioate esters in DMSO/water mixtures

The hydrolysis rates of the dianions of phosphate and phosphorothioate esters are substantially accelerated by the addition of polar aprotic solvents such as DMSO and acetonitrile. The activation barrier DeltaG is smaller due to a lower enthalpy of activation. The enthalpy of transfer of p-nitrophenyl phosphate (pNPP) and p-nitrophenyl phosphorothioate (pNPPT), from water to 0.6 (mol) aq DMSO (60 mol % water in DMSO) were measured calorimetrically. The enthalpies of activation for the hydrolysis reactions in the two solvents permitted the calculation of the enthalpy of transfer of the transition states. This transfer is thermodynamically favorable for both the reactants and the transition states but is more favorable for the transition states. In the case of pNPP, the enthalpy of transfer of the reactant is -23.9 kcal/mol, compared to -28.3 for the transition state. The difference is greater for pNPPT, where the enthalpy of transfer of the reactant is -23.2 kcal/mol and that for the transition state is -35.3. The results show that the reduced enthalpies of activation in both hydrolysis reactions arise not from a destabilization of the reactants in the mixed solvent, but from the fact that the enthalpy of transfer of the transition states to the mixed solvent is significantly more negative than the enthalpy of transfer of the reactants.     

DMSO作为新的合成子在有机合成中的应用研究进展

二甲亚砜(DMSO)不但可以作为有机溶剂,同时还可以作为反应试剂,在有机合成中得到了广泛的应用.由于其具有来源广、价格低廉、操作简单等优点,近年来将DMSO作为反应试剂应用于有机合成反应引起了广大化学家的关注.本文作者对近几年来DMSO作为合成子在有机合成中的应用按照引入官能团的种类进行了总结,详细阐述了其转化为甲磺酰基、甲酰基、氰基、甲硫基等官能团的方法学研究,以期为开发DMSO新的应用提供参考依据.     

Selective synthesis of 4-hydroxybenzoic acid using immobilized cyclodextrin

-cyclodextrin immobilized with epichlorohydrin was used for the selective syntheses of 4-hydroxybenzoic acids from phenols and carbon tetrachloride in aqueous sodium hydroxide solutions. The selectivities were 100 %, and the yields were larger than 80 mole%. The immobilized catalysts were easily separated from the reaction mixture, and were repeatedly used without measurable decrease in the catalytic activity.     

Recent advances in the synthesis of cyclodextrin derivatives under microwaves and power ultrasound

We describe improved syntheses of CD derivatives, like 6^I-monotosyl, 6^I-monoazido-6^I -monodeoxy, 6^I-monoamino-6^I-monodeoxy-βCD and 2^I-O-mono(methylamino)alkyl-βCDs, that were carried out under US or MW, to great advantage in terms of yield, purity and reaction time. In the search for more efficient procedures to prepare monosubstituted CDs, we applied MW and/or US to some fundamental preparations such as those of 6^I-amino-6^I-deoxy-βCD and a series of 2-monoaminomethyl-βCD derivatives.     

Contribution to the synthesis of chiral allenic esters

A phosphorus ylide bearing a 10-phenylsulfonylisoborneol unit reacted with ketenes, generated in situ from acid chlorides and triethylamine, to give allenic compounds. The reaction with methylketene led to asymmetric induction with the selective synthesis of an allene with axial chirality corresponding to an S configuration. The structure of the chiral allene 10-phenylsulfonylisobornyl penta-2,3-dienoate was determined by X-ray crystallography. Chirooptical studies of the chiral allene derivatives were done.     

Strategies for the asymmetric synthesis of H-phosphinate esters

Access to P-chiral H-phosphinates via desymmetrization of hypophosphite esters was investigated. The use of chiral auxiliaries, chiral catalysts, and of a bulky prochiral group that could lead to kinetic resolution was explored. A chiral NMR assay for enantiomeric excess determination of H-phosphinates was developed. An asymmetric route to C-chiral H-phosphinates is also examined and an assay was developed.