Stereoselective synthesis of syn-β-amino esters using the TiCl4/R3N reagent system

The reactions of benzaldehyde imines and esters with the TiCl₄/R₃N reagent system give syn-β-amino esters as the major products in 38-87% yields.     

Preparation and properties of carboxyl-functional mixed esters of hydrolyzed starch

Mixed esters of hydrolyzed starch represent a new class of chemically modified natural polymers demonstrating a broad range of properties. Members of this class of polymers have both neutral aliphatic ester side chains and carboxyl-functional half-ester side chains. Use of hydrolyzed starch as the backbone polymer results in products that are considerably lower in molecular weight than whole starch derivatives, but which are still polymeric in character. Synthesis proceeds smoothly in pyridine using anhydrides as acylating agents and the pure solid mixed ester products are isolated by precipitation in water. Measurement of degree of substitution (D.S.) by NMR or hydrolysis characterizes the chemical composition of the polymers. The actual D.S. achieved in the synthesis depends upon the competition between starch and residual water for anhydrides, which can be quantitatively evaluated by monitoring the acid content of the reaction mixture. The T_g and T_s of starch mixed esters vary with both D. S. and length of the aliphatic ester side chain. As the composition changes from acetate—phthalate to butyrate—phthalate a T_g range of greater than 100°C is observed. Hydrolyzed starch mixed esters are hydrophobic and organic-soluble, but may be readily solubilized in aqueous base through the half-ester groups. Solutions show surface activity which varies according to the type and extent of substitution.     

Synthesis of α1-(Cbz-aminoalkyl)-α2-(hydroxyalkyl)phosphinic esters

A synthesis of α₁-(Cbz-aminoalkyl)-α₂-(hydroxyalkyl)phosphinic esters was achieved by the 1,2-addition of the appropriate aldehyde to Cbz-protected phosphinic analogues of amino acid esters in the presence of at least three equivalents of trimethylsilyl chloride and NEt₃. The complete deprotection of the product esters could be achieved in one step using 35% HBr in acetic acid.     

S-Trifluoromethyl esters of thiocarboxylic acids, RC(O)SCF3

S-Trifluoromethyl esters of different types of thiocarboxylic acids have been prepared in moderate to excellent yields from halide substitution reactions of the corresponding acid chlorides and tetramethylammonium trifluoromethylthiolate. C₆F₅C(O)SCF₃ undergoes a surprising rearrangement on attempted isolation to give 4-CF₃SC₆F₄C(O)F, which was converted into the corresponding acid.     

Fluorolactonization of norbornenecarboxylic acids and their methyl esters with F-TEDA-BF4 and XeF2

The selective fluorolactonization was achieved by treatment of cis-5-norbornene-2,3-endo-dicarboxylic acid or its monomethyl and dimethyl esters with F-TEDA-BF₄ or XeF₂. The reactions of 5-norbornene-endo-2-carboxylic acid and its monomethyl ester with F-TEDA-BF₄ or XeF₂ proceed in a non-selective manner to give fluorolactonization, addition and rearrangement products. The basic factor responsible for selectivity of the fluorolactonization is the presence of two endo-oriented carboxyl groups in the substrate molecule. The electrophilicity and type of the fluorinating agent is of secondary importance in this regard. It is postulated that the fluorolactonization of norbornenecarboxylic acids and their methyl esters with F-TEDA-BF₄ or XeF₂ is realized mainly via “open” fluoronorbornyl carbocation intermediates which in the reaction with XeF₂ are postulated as the tight ion pairs.     

Mass spectra of halogenated esters. 7. Methyl esters of 2-chloro C2?C20 n-alkanoic acids

The mass spectral fragmentation of a homologous series of methyl esters of 2-chloro n-alkanoic acids ranging from acetic (C₂) to eicosanoic (C₂₀) acid on electron impact has been investigated. The fragmentation pathways were elucidated with the aid of the first field-free region metastable ions, the results being presented with one compound, i.e. with ionized methyl 2-chloro-octauoate. Owing to the Cl/H exchanges and to the formation of the non-chlorinated parent esters prior to the fragmentations the spectra show the peak pairs with and without the chlorine atom. The effects become more evident with increasing chain length; shown most visually by the abundance ratios of the McLafferty rearrangement ions atm/z108/110 and 74, and fragments at m/z121/123 and 87.     

Vapor phase synthesis of phthalate esters from benzene and maleic anhydride over CrO3/magnesol and SO42-/ZrO2+

Benzene and maleic anhydride react over solid acids, viz. CrO₃/Magnesol and SO₄ ^2-/ZrO₂ catalysts to form phthalic anhydride and olefins, which in turn produce phthalate esters as end products. Based on the product distribution, a reaction pathway is proposed.     

Synthesis of cationic water-soluble esters of chlorin e6

Two esters of chlorin e₆ have been synthesized by esterification with aminoalcohols via the formation of acid chloride using oxalyl chloride and converted to the corresponding cationic water-soluble esters of chlorin e₆. The visible absorption and circular dichroism spectra have revealed that these two cationic chlorin e₆ esters synthesized are readily soluble in water as a monomer.     

Mass spectra of halogenated esters 5—Chloromethyl esters of aliphatic C2?C12 n-carboxylic acids and their monochlorinated derivatives

A study has been made of the mass spectral fragmentation upon electron impact of aliphatic C₂? C₁₂ chloromethyl esters and all their 66 monochlorinated derivatives. The fragmentation pathways of the parent chloromethyl esters were elucidated with the aid of the 1st FFR metastable ions. A McLafferty rearrangement gives the base peak in the C₆? C₁₁ parent esters and in almost all the 4-chloro and ω-chloro isomers. The subsequent loss of HCl gives a very characteristic peak of the chloromethyl esters and their (3-ω)-chloro derivatives at m/z 72, [C₃H₄O₂]⁺. The 2-chloro isomers have the corresponding chlorine-containing fragment ion at m/z 106/108. The mass spectra of 2-, 3-, 4-, 5- and ω-chloro isomers give the characteristic fragment ions, the mass spectra of the other isomers being very similar.     

Synthesis of cis-2-aryl-3-pyrrolidine carboxylic esters via diastereoselective cyclization of γ-imino esters using a TiCl4/Et3N reagent system

Facile synthesis of cis-2-aryl-3-pyrrolidine carboxylates from readily accessible γ-imino esters by intramolecular cyclization mediated by a TiCl₄/Et₃N reagent system is described.     

Structure and Characterization of the [Rbx (NH4)1-x]2TeCl6 Tellurate Family at Room Temperature

The crystal structure of rubidium-ammonium hexachlorotellurate [Rb_0.94(NH₄)_0.06]₂TeCl₆ was determined by X-ray single crystal analysis at room temperature. The space group is Fm3m with the lattice parameter a = 10.2503(5) ? and Z = 4. The refinement converged to R(F) = 0.015 and wR(F ²) = 0.032. As in the studied [Rb0.94(NH₄)₀.06]2TeCl6 family, this compound has an antifluorite-type arrangement. Tellurium atoms are surrounded by an octahedron of chlorine atoms. The Rb or N atoms are located between TeCl₂⁶ octahedra ensuring the stabilization of the structure by ionic and hydrogen bonding contacts N-HCl. The substitution of rubidium by ammonium groups does not affect the structural arrangement, but it leads to a decrease in the a lattice cell dimension. IR and Raman spectroscopic studies at room temperature were performed to confirm the X-ray crystallographic results.     

Mass spectra of chlorinated esters: 2—Methyl mono- and dichlorobutanoates

The mass spectral fragmentations of methyl mono- and dichlorobutanates have been studied. Deutrium labelling and metastable ion analysis were used to elucidate the fragmentation mechanisms. The molecular ion peaks of the esters are weak and show only in the spectra of the monochloro isomers. A McLafferty rearrangement gives the base peaks in the spectra of methyl 2-chloro-, 4-chloro- and 4,4-dichlorobutanoate; α-cleavage, [COOCH₃]⁺, in methyl 2,2- and 2,4-dichlorobutanoate; [M? Cl]⁺, in methyl 3-chlorobutanoate; [M? Cl? HCl]⁺, in methyl 3,4-dichlorobutanoate; [M? Cl? CH₂CO]⁺, in methyl 3,3-dichlorobutanoate and [M? Cl? COOCH₃]^+˙, in methyl erythro- and threo-2,3-dichlorobutanoate. The mass spectra of the stereoisomers are nearly identical, the loss of a chlorine atom and the McLafferty rearrangement giving the higher peaks in the spectrum of the threo form.     

稀土元素取代对Ti_(0.26)Zr_(0.07)V_(0.24)Mn_(0.1)Ni_(0.33)贮氢合金结构和电化学性能的影响

研究了5种稀土元素部分取代V对Ti0.26Zr0.07V0..24Mn0.1Ni0.33合金的微观结构和电化学性能的影响。结果表明,Ti0.26Zr0.07V0.24Mn0.1Ni0.33和Ti0.26Zr0.07V0.24-xMn0.1Ni0.33REx(x=0.005;RE=La,Ce,Nd,Ho,Y)均由体心立方结构的钒基固溶体相和六方结构的C14 Laves相组成。在合金中加入稀土元素,会使合金中两相的晶胞体积同时增大。稀土元素部分取代V均改善了合金电极的活化性能。La和Nd元素取代后,合金电极的最大放电容量明显增加,而Ce的取代提高了合金电极的循环稳定性。Ce,Nd,Ho,Y均改善了合金电极的倍率放电性能。合金电极在高温状态下表现出了良好的放电性能,其中Nd在333 K时放电容量可达550.4 mAh·g-1。稀土元素对荷电保持率的影响各异。     

稀土元素取代对Ti0.26Zr0.07V0.24Mn0.1Ni0.33贮氢合金结构和电化学性能的影响

研究了5种稀土元素部分取代V对Ti_0.26Zr_0.07V_0..24Mn_0.1Ni_0.33合金的微观结构和电化学性能的影响。结果表明,Ti_0.26Zr_0.07V_0.24Mn_0.1Ni_0.33和Ti_0.26Zr_0.07V_0.24-xMn_0.1Ni_0.33RE_x（x=0.005;RE=La,Ce,Nd,Ho,Y）均由体心立方结构的钒基固溶体相和六方结构的C14Laves相组成。在合金中加入稀土元素,会使合金中两相的晶胞体积同时增大。稀土元素部分取代V均改善了合金电极的活化性能。La和Nd元素取代后,合金电极的最大放电容量明显增加,而Ce的取代提高了合金电极的循环稳定性。Ce,Nd,Ho,Y均改善了合金电极的倍率放电性能。合金电极在高温状态下表现出了良好的放电性能,其中Nd在333K时放电容量可达550.4mAh·g^-1。稀土元素对荷电保持率的影响各异。     

Secondary kinetic isotope effects: Deuterium abstraction by chlorine atoms from the CD3 group in CD3CH2Cl,CD3CHDCl,and CD3CD2Cl

The occurrence and magnitude of secondary kinetic isotope effects in the gas phase has been determined for deuterium abstraction from the CD₃ group in CD₃CH₂Cl, CD₃CHDCl, and CD₃CD₂Cl by photochemically generated ground-state chlorine atoms. Over the temperature range 10–94°C a discernible “inverse” kinetic isotope effect is observed. Both the pre-exponential factors and activation energies decrease with deuterium substitution in the vicinal chloromethyl group. The opposing trends result in a net effect close to unity.     

The influence of micellization ofn-decylamine on its basicity and reactivity toward carboxylic acid esters

Micellization ofn-decylamine in aqueous solution leads to substantial decrease in its pK _a, and increase in its reactivity in the nucleophilic substitution ofp-nitrophenylic esters of carboxylic acids (up to 70 times compared to ethylamine which forms no micelles). The influence of cetylpyridinium bromide on the acid-base properties ofn-decylamine and its reactivity was investigated. It was found that the reaction withn-decylamine can be accelerated or retarded depending on the hydrophobicity of the esters. The quantitative characteristics of the mieellar catalytic processes were estimated.Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 2, pp. 366–370, February, 1996.     

Halogenation of unsaturated esters—III : Reactions of bromine chloride with chlorinated methyl 2-butenoates

Additions of Cl₂, Br₂; and BrCl to methyl Z-2-chloro-2-(1), E-3-chloro-2-(2), Z-3-chloro-2-(3) and E-4-chloro-2-butenoates (4) in CCl₄ both in the dark and light have been investigated. The product compositions are compared with those reported previously for methyl monochloropropenoates. The chlorine substitution was found to affect the product distributions in the reactions with the BrCl reagent. Under the ionic conditions Br₂ adducts were the main products from 1 and 2, whereas 3 reacted like methyl Z-3-chloropropenoate giving only negligible amount of the Br₂ addition. The Cl₂ addition amounted, as in the reactions of methyl monochloropropenoates, to only a few percent. Compared with the parent esters the chlorine substitutions in 2, 3 and 4 also affected the regiochemistry of the BrCl addition. The main regioisomer in the dark, i.e. the 2-bromo-3-chloro adduct, was obtained from 3, as from methyl Z-3-chloropropenoate, with almost complete regioselectivity. Compound 4 also showed greater regioselectivity than methyl E-2-butenoate. Substrate 2 was, however, found to produce more 3-bromo-2-chloro adduct than the unchlorinated parent ester. Mechanisms presented for the additions of BrCl to methyl 3-chloropropenoates are reconsidered on the basis of the results from the present study.     

Novel cellulose derivatives. IV. Preparation and thermal analysis of waxy esters of cellulose

Cellulose esters with linear aliphatic acyl substituents ranging in size from C₁₂ (lauric acid) to C₂₀ (eicosanoic acid) were prepared in homogeneous solution (DMAc/LiCl) using a novel synthetic method based on the use of a mixed p-toluenesulfonic/carboxylic acid anhydride. The resulting waxy cellulose esters had a high degree of substitution (DS), between 2.8 and 2.9, and showed little degradation. Thermal analysis of these cellulose derivatives by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) revealed a series of transitions that represented motion by both ester substituents and cellulosic main chain. Broad crystallization and melting transitions attributed to side-chain crystallinity were observed in the range between −19 and +55°C; these side-chain T_m and T_c transition temperatures increased by 10°C per carbon atom of the ester substituent. The T_g of these derivatives increased linearly with increasing substituent size from 94°C for C₁₂ (cellulose laurate) to 134°C for C₂₀ (cellulose eicosanoate). Evidence of “main-chain” crystallization was not observed for these samples, except in the case of peracetylated C₁₂ and C₁₄ esters, which had T_m values of 96°C and 107°C, respectively. © 1996 John Wiley & Sons, Inc.     

A novel arylation of arylacetic acid esters using tertiary arylamines and TiCl4

The reactions of arylacetic acid esters with tertiary arylamines in the presence of TiCl₄ give α-arylated products in 65-90% yields, as well as 10-20% yields of the corresponding benzidines.     

29Si and 13C NMR spectra of chloro- and fluoro-substituted linear permethylpolysilanes

²⁹Si and ¹³C NMR spectra are reported for the three halopolysilane series Me(SiMe₂)_nCl, Cl(SiMe₂)_nCl and F(SiMe₂)_nF, where n = 2 to 6. Except for the dihalodisilanes (XSiMe₂)₂, data for all of the compounds fit linear relationships based on substituent constants for chlorine or fluorine atoms in the α, β and γ positions. The effects of halogen substitution on ²⁹Si and ¹³C chemical shifts are rapidly attenuated along the polysilane chain, becoming negligible four atoms away from the halogen. The NMR data provide no evidence for long-range electronic transmission from chlorine or fluorine in halopermethylpolysilanes of the type suggested by other workers [1].