Determination of acidity constants of pyridines,imidazoles, and oximes by capillary electrophoresis

The acidity constant in the form of pK_a is one of the most important physicochemical quantities. There are prediction tools available for calculating the pK_a, but they only deliver precise calculated values for a relatively small set of chemicals. For complex structures with multiple functional groups in particular, the error in the predicted pK_a is high due to the application domain of the corresponding models. Thus, we aim to enlarge the dataset of experimentally determined pK_a values using capillary electrophoresis. We, therefore, selected various pyridines, imidazoles, and oximes to determine the pK_a values using the internal standard approach and the classical method. Especially oximes were not investigated in the past, and predictions for them include larger errors. Thus, our experimentally determined values could contribute to an improved understanding of various functional groups impacting the pK_a values and serve as additional datasets to develop improved pK_a prediction tools.     

噁二唑并[5,4-d][1,5]苯并硫氮杂衍生物的合成、表征及晶体结构

以1,5-苯并硫氮杂(1a～1o)为原料, 在三乙胺作用下与α-氯代喹喔啉-2-甲醛肟(2)发生1,3-偶极环加成反应得到一系列噁二唑并[5,4-d][1,5]苯并硫氮杂衍生物3a～3o. 产物的结构经元素分析、IR和1H NMR确认. 并用X射线衍射法测定了化合物3a的晶体结构. 化合物3a属三斜晶系, 空间群P-1, 晶胞参数: a＝0.97376(19) nm, b＝1.0017(2) nm, c＝1.3526(3) nm, α＝78.50(3)°, β＝84.30(3)°, γ＝68.26(3)°, Mr＝486.58, V＝1.2005(4) nm3, Dc＝1.346 Mg/m3, Z＝2, F(000)＝508.     

Gold(I)‐Catalyzed Diastereo‐ and Enantioselective Synthesis of Polysubstituted Pyrrolo[3,4‐d][1,2]oxazines

A gold(I)‐catalyzed highly diastereo‐ and enantioselective intermolecular cycloaddition of oxime ethers with nitrones under mild conditions was developed, which provides an facile access to optically pure highly substituted pyrrolo[3,4‐d][1,2]oxazines. The salient features of this reaction include general substrate scope, high efficiency, high enantioselectivity, readily available starting materials, and the use of commercially available ligand.     

铌酸催化合成环己酮1,2-丙二醇缩酮

将铌酸应用于催化缩酮反应，以环己酮和1，2－丙二醇的缩酮反应为探针，详细探索了影响缩合反应的各种因素，并得出了铌酸催化环己酮与丙二醇反应的最佳条件：mol环己酮：mol丙二醇＝1：1.5，环己烷作带水剂，环己烷和铌酸催化剂的用量分别为反应物总体积、总质量的35％和1．2％，回流搅拌反应3.5h，产品环己酮1，2－丙二醇缩酮的总收率为73．5％。     

Palladium-catalyzed oxime ether directed regioselective C-H alkoxylation of arenes

A palladium-catalyzed highly regioselective ortho-C(sp²)-H alkoxylation of oxime ethers with PhI(OAc)₂ as the oxidant and alcohols as the alkoxylation reagents has been developed. Mono-alkoxylated and acetoxylated products could be selectively obtained via tuning the reaction conditions. A series of oxime ethers were tolerated, affording the corresponding products in moderate to good yields. Both primary and secondary alcohols survived the reaction conditions. Moreover, the directing group can be easily removed, thereby providing a straightforward access to substituted aryl ketones.     

Design,Synthesis, and Bioassay of Novel Compounds of Isolongifolenone Oxime Derivatives

A succession of new isolongifolenone oxime derivatives have been designed and synthesized. The structures of these compounds were identified by IR, ¹H‐NMR, ¹³C‐NMR, mass spectra, and elemental analysis. The bioassays of antibacterial, antifungal, and insecticidal activity were carried out. The in vitro antibacterial and antifungal activities were evaluated by the disk diffusion method, and the minimum inhibitory concentration was determined by the microdilution method, while the insecticidal activity was tested by the spraying method or the straw impregnation method. The results of bioassays showed that compound 3f was more active in resisting all the tested bacterial and fungal organisms when compared to the standard drug amoxicillin at the lowest concentration of 31.3 μg/ml. Compound 4 , synthesized by Beckmann rearrangement reaction of isolongifone oxime, exerted moderate insecticidal activity against soybean aphid. Furthermore, compound 3m exhibited more activity in killing armyworms than the standard drug flucycloxuron at the concentration of 0.5 mg/l.     

In vitro antifungal activity of flavonoid diglycosides of Mentha piperita and their oxime derivatives against two cereals fungi

Flavonoids due to their various interesting biological properties such as antifungal activity were investigated in Mentha piperita leaves. The butanolic fraction obtained from the hydro-alcoholic crude extract of M. piperita is rich in flavonoids; it reduced in vitro the mycelium growth of Phoma sorghina and Fusarium moniliforme around 72% and 55%, respectively, when used at a concentration of 5 mg/ml. In addition, the chemical conversion of the flavonoids in the butanolic fraction into their oxime derivatives increased the antifungal activity since the percentage of inhibition increased to 84% and 65% against P. sorghina and F. moniliforme, respectively, at 5 mg/ml. Butanolic fraction and oxime inhibition effects on spore germination of the two fungi were also observed. These results suggest that, M. piperita flavonoids could be used as botanical fungicides to protect cereals against infection from P. sorghina and F. moniliforme.     

Silica sulfate as an efficient recyclable catalyst for protection of α-hydroxy acids with cyclohexanone

Silica sulfate has been found to be an effective catalyst for protection of α-hydroxy acids under mild reaction conditions. Although the reaction can be carried out in diethyl ether, a remarkable rate enhancement was observed when the reaction was carried out under solvent-free condition. The catalyst could also be recovered and reused without any significant loss of reactivity. A wide range of α-hydroxy acids could be protected using cyclohexanone derivatives in high yield in presence of silica sulfate catalyst at room temperature.     

A CLEAN CONVERSION OF CARBONYL COMPOUNDS TO OXIMES USING SILICA GEL SUPPORTED HYDROXYLAMINE HYDROCHLORIDE

The efficient condensation of carbonyl compounds with hydroxylamine hydrochloride under solvent free conditions is described.     

Aluminiumorganic compounds of some metaldioximates

Coordinated dioximes with nickel(II), palla‐dium(II) and copper(II) ions proved capable of giving substitution reactions with a series of aluminiumorganic compounds. Studies made on the reaction products have revealed that in the case of both dimethylglyoxime and diphenylglyoxime. The reaction products result from substitution of the O? H…O hydrogen bridges existing in such compounds by O? Al? O bridges. All compounds reported in this paper were separated from the reaction mixture as coloured powders and were characterized by chemical analyses, IR spectroscopy, X‐ray diffraction spectra, proton NMR spectra and magnetic properties. Copyright © 2001 John Wiley & Sons, Ltd.