An efficient synthesis of isothiazolidines via sulfonium ylides formed by the reaction of thietanes and nitrene

An efficient synthesis of isothiazolidines in good yields is described.     

The stereoselective synthesis of novel macrolide antibacterial agents via an intramolecular 1,3-dipolar cycloaddition of azomethine ylide

An intramolecular 1,3-dipolar cycloaddition of azomethine ylide, generated in situ via the reaction of C12-glycinate derivative of macrolide with formaldehyde, provided a novel tricyclic macrolide. The high stereoselectivity of this [2+3] reaction was achieved by introducing a suitable directing group at C-6 position of macrolide.     

Highly Stereoselective Synthesis of trans-3-Aryl-4-carbethoxy-2,3-dihydro-2-fur-2＇-oyl-5-methylfurans

Multi-substituted dihydrofurans are valuable intermediates for the synthesis of natural products and pharmaceuticals. Considerable attention has been focused on the development of efficient and regioselective methods for their preparation. Using K2CO3 as a base, with the reaction of fur-2-oylmethyltriphenylarsonium bromide 1 and ethyl 2-acetyl-3-arylacrylate 2 in tetrahydrofuran at room temperature, we found an efficient protocol was achieved to synthesize trans-3-aryl-4-carbethoxy-2,3-dihydro-2-fur-2＇-oyl-5-methylfurans 3 in good yield with high stereoselectivity. The structure of compound 3 was confirmed by IR, ^1H NMR, MS and HRMS. The mechanism for the formation of 3 was proposed.     

Strukturen neuer SeII- und TeII-Komplexe mit 2,2-Dicyanethylen-1,1-dithiolat, 2,2-Dicyanethylen-1,1-thioselenolat und 2,2-Dicyanethylen-1,1-diselenolat

Structures of New Se^II and Te^II Complexes Containing 2,2-Dicyanethylene-1,1-dithiolate, 2,2-Dicyanethylene-1,1-thioselenolate, and 2,2-Dicyanethylene-1,1-diselenolate (NBu₄)₂{Se[S₂C?C(CN)₂]₂} ( I ), (AsPh₄)₂ · {Te[SSeC?C(CN)₂]₂} ( II ), and (NBu₄)₂{Te[Se₂C?C(CN)₂]₂} ( III ) containing the bidentate chelate ligands 2,2-dicyanethylene-1,1-dithiolate i-mnt , 2,2-dicyanethylene-1,1-thioselenolate i-mnts , and 2,2-dicyanethylene-1,1-diselenolate i-mns have been prepared and characterized by X-ray structure analysis. The central units consist of [M(X? X)₂E₂]^2? (M = Se, Te; X? X = ligand; E = lone-pair) with fourfold coordinated Se^II and Te^II, respectively. The complex anions [Se(i-mnt)₂E₂]^2? as well as [Te(i-mnts)₂E₂]^2? show a trapezoide distortion with d(Se? S) = 2.276(5); 2.287(5); 2.803(5); 2.789(5) Å and d(Te? Se) = 2.611(2); 2.617(3); d(Te? S) = 2.889(5); 2.935(4) Å. In III there are centrosymmetric complex anions [Te(i-mns)₂E₂]^2? with nearly identical Te? Se-bond-lengths: 2.674(3) and 2.692(2) Å. These Te? Se bonds are elongated compared to usual Te? Se bonds.     

Synthesis of stable azomethine ylides by the rearrangement of 1,3-dipolar cycloadducts of 3,4-dihydroisoquinoline-2-oxides with DMAD

1-Aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines were prepared according to a one-pot procedure involving the reaction of 2-(3,4-dimethoxyphenyl)-ethylamine with aromatic aldehydes in TFA at reflux. The tetrahydroisoquinolines were treated with H₂O₂-WO₄²⁻ in methanol at room temperature to give the corresponding 3,4-dihydroisoquinoline-2-oxides. Treatment of these cyclic nitrones with DMAD in toluene at room temperature gave the corresponding isoxazolo[3,2-a]isoquinolines. These compounds were heated in toluene at reflux to give the corresponding ylides in high yields (Method A). The effect of the substituents on the rate of the rearrangement of such compounds prompted us to discuss a new mechanism involving consecutive C-C bond heterolysis and 1,3-sigmatropic shift. A one-pot reaction involving the treatment of the nitrones with equimolar amounts of DMAD in refluxing toluene also gave the ylides (Method B). The structures of the prepared compounds were elucidated by spectral means and elemental analyses.     

膦、胂叶立德的化学与应用——Ⅰ.用红外光谱对膦、胂叶立德结构的研究

以78个带吸电子取代基的膦、胂叶立德的红外光谱的解析为根据,讨论了它们的结构及其与光谱的关系。     

Dynamic stability of carbonyl ylides

The non- and fluorine-substituted singlet carbonyl ylides are studied by using ab initio MCSCF calculations. The thermodynamic stability of the carbonyl ylides and the intramolecular stability to isomerization or fragmentation reaction coordinates is demonstrated in terms of the topological structure of the ab initio potential energy surfaces. The allylic resonance is found to be dynamically unstable, considering out-of-plane vibrational mode. The instability is studied by the symmetries of the low-lying excitations out of the MCSCF wave function.     

Structural integration of tellurium oxide into mixed-network-former glasses: connectivity distribution in the system NaPO(3)-TeO(2).

Sodium phosphate tellurite glasses in the system (NaPO(3))(x)(TeO(2))(1-) (x) were prepared and structurally characterized by thermal analysis, vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS) and a variety of complementary solid-state nuclear magnetic resonance (NMR) techniques. Unlike the situation in other mixed-network-former glasses, the interaction between the two network formers tellurium oxide and phosphorus oxide produces no new structural units, and no sharing of the network modifier Na(2)O takes place. The glass structure can be regarded as a network of interlinked metaphosphate-type P(2) tetrahedral and TeO(4/2) antiprismatic units. The combined interpretation of the O 1s XPS data and the (31)P solid-state NMR spectra presents clear quantitative evidence for a nonstatistical connectivity distribution. Rather, the formation of homoatomic P--O--P and Te--O--Te linkages is favored over mixed P--O--Te connectivities. As a consequence of this chemical segregation effect, the spatial sodium distribution is not random, as also indicated by a detailed analysis of (31)P/(23)Na rotational echo double-resonance (REDOR) experiments.     

Differential pulse voltammetric determination of trace Te(IV) at a poly(3,3′-diaminobenzidine) film modified gold electrode in flow systems

Electropolymerization of 3,3′-diaminobenzidine on a gold surface gave an adherent, stable film of poly(3,3′-diaminobenzidine) (PDAB). This polymer film retained the complexational functionalities of its monomer, demonstrating preconcentration abilities for several ions, including Se(IV) and Te(IV). In particular, in this work, continuous flow and flow injection methods were developed for the sensitive and selective determination of Te(IV). The optimized method for the continuous flow mode had a detection limit of 5.6×10⁻⁹ mol l⁻¹ for 10 min preconcentration. Typical relative standard deviations for six consecutive determinations were 1.82 and 2.56% for Te(IV) concentrations of 1.0×10⁻⁶ and 5.0×10⁻⁸ mol l⁻¹, respectively (10 min preconcentration). The method was applied to the determination of Te(IV) in real samples.