Organotin–oxotungstate coordination polymer: An efficient catalyst for the selective oxidation of amines

The organometallic coordination polymer [(nBu₃Sn)₂WO₄] catalyzed the selective oxidation of secondary and primary amines to nitrones and oximes, respectively. The catalyst was found to be reusable for five catalytic cycles without any appreciable loss in activity. Under the optimized reaction conditions [4 mol% catalyst, 3–4 equiv of hydrogen peroxide (30 wt%, aqueous solution), methanol as the solvent, r.t.], the corresponding nitrones and oximes were obtained with good efficiency.     

Double nucleophilic N-alkylation of α-oxime-esters with Grignard reagents

Double nucleophilic N-alkylation of α-oxime-esters, affording N,N-dialkyl-α-amino acids is herein described. Grignard reagents accomplished double N-alkylations via umpolung and various N,N-dialkylated α-amino acids were successfully synthesized in 15 min. Both electron-withdrawing sulfonyl groups and electron-donating silyl and methyl groups on oximes were available. Alkylmagnesium species and (E)-configuration of α-oxime-ester were essential to this cascade reaction.     

DNA Binding and Cleavage Activity of cis‐Cobalt Aromatic Oxime Complexes and Its Pyridine/imidazole Adducts

cis‐Cobalt complexes with salicycaldoxime(SAO), (Z)‐1‐(2‐hydroxyphenyl)ethanonoxime (HEO), (Z)‐1‐(2,5‐dihydroxyphenyl)ethanonoxime (DEO), (Z)‐1‐(2,5‐dihydroxyphenyl)(phenyl)methanonoxime (DPO) and their adducts with pyridine (Py) and imidazole (Im) were synthesized and characterized by elemental analysis, magnetic susceptibility, UV‐Vis and IR spectra. The electrochemical studies were carried by cyclic voltammeter, the peak potential separation and formal potential of complexes were independent of sweep rate or scan rate (ν) indicating a quasi reversible one‐electron redox process. Absorption studies and thermal denature studies revealed that each of these octahedral complexes is an avid binder of calf thymus DNA. The apparent binding constants for mixed ligand complexes are in order of ～10³‐10³ M^?1. Based on the data obtained in the DNA binding studies a partial intercalative mode of binding is suggested for these complexes. The nucleolytic cleavage activity of parent complexes and their pyridine adduct were carried out on double stranded pBR322 circular plasmid DNA by using a gel electrophoresis experiment in the presence and absence of oxidant (H₂O₂). All the metal complexes show enhanced cleavage activity in presence of oxidant. The hydrolytic cleavage of DNA of Co(DEO)₂ and Co(DPO)₂ is evidenced from the control experiments showing discernable cleavage inhibition in the presence of the hydroxyl radical inhibitor DMSO and EDTA.     

Metal‐Free 2,2,6,6‐Tetramethylpiperidin‐1‐yloxy Radical (TEMPO) Catalyzed Aerobic Oxidation of Hydroxylamines and Alkoxyamines to Oximes and Oxime Ethers

TEMPO‐Mediated oxidation of hydroxylamines (=hydroxyamines) and alkoxyamines to the corresponding oxime derivatives is reported (TEMPO=2,2,6,6‐tetramethylpiperidin‐1‐yloxy radical; Scheme 2). These environmentally benign oxidations proceed in good to excellent yields (Table 1). For alkoxyamines, oxidation to the corresponding oxime ethers can be performed by using dioxygen as a terminal oxidant in the presence of 5–10 mol‐% of TEMPO or 4‐substituted derivatives thereof as a catalyst (Scheme 3 and Table 2). Importantly, benzyl bromides can directly be transformed to oxime ethers via in situ alkoxyamine formation by a nucleophilic substitution followed by TEMPO‐mediated oxidation (Scheme 4 and Table 3).     

Synthesis,characterization, and ascorbic acid oxidase biomimetic catalytic activity of cobalt(III) oxime complexes

A new tetradentate tetraaza ligand was prepared via Schiff-base condensation of 3,4-diaminotoluene with 2,3-butandione monoxime in aqueous solution. This ligand coordinates cobalt(III) through nitrogen donors in equatorial positions with loss of one oxime proton with concomitant formation of an intramolecular hydrogen bond. A series of cobalt(III) complexes, [CoLX₂] (X?=?Cl^?, Br^?, or I^?), [SCNCoLBr], [CNCoLBr], [BF₂CoLBr], and [YCoLBr]ClO₄ (Y?=?pyridine, thiophene, triphenylphosphine, or n-pentylamine), was synthesized. The compounds were characterized based on the elemental analysis (C, H, N), electrical conductance, magnetic moment measurements, and spectral studies (IR, ¹H NMR, and UV-Vis). Thermal stabilities of representative complexes were examined by using thermal analysis (TGA and DTG). The reported complexes are d⁶ low-spin diamagnetic and a distorted octahedral environment was proposed. All complexes undergo tetragonal distortion as evidenced by splitting of ¹T_1g and ¹T_2g levels of the pseudo-octahedral symmetry. The ligand field parameters such as Dq^E , Dq^A , and the tetragonal splitting D_t have been computed and correlated with the nature of the coordinated axial ligands. The reported cobalt(III) complexes exhibit promising catalytic activity toward aerobic oxidation of ascorbic acid to the corresponding dehydroascorbic acid. The oxidase catalytic activity is linked to both the tetragonal splitting parameter D_t and the Lewis-acidity of cobalt(III) created by the nature of the coordinated axial ligands. The probable mechanistic implications of the catalytic oxidation reactions are discussed.     

A conjugate addition/dipolar-cycloaddition cascade sequence for the synthesis of (±)-cylindricine C

An efficient stereocontrolled route to (±)-cylindricine C is described. Reaction of 9-hydroxynon-1-en-5-one oxime with 2,3-bis(phenylsulfonyl)-1,3-butadiene affords a 7-oxa-1-azanorbornane cycloadduct in high yield. The formation of the bicyclic isoxazolidine arises from conjugate addition of the oxime onto the diene to give a transient nitrone that spontaneously undergoes an intramolecular dipolar cycloaddition. The resulting cycloadduct derived from the cascade sequence was converted into (±)-cylindricine C by: (1) a reductive-cyclization to set the BC-ring skeleton, (2) a base-induced cyclization to construct the tricyclic core, and (3) an oxidation-conjugate addition of the n-hexyl side chain to complete the synthesis.     

Low-valent zirconocene-mediated cyclization of γ,δ-unsaturated oximes

γ,δ-Unsaturated O-methyl oximes were cyclized to dihydropyrrole by the treatment of (1-butene)ZrCp₂3 prepared by Negishi’s procedure (reaction with Cp₂ZrCl₂ and two equivalents of n-BuLi). In this cyclization, the geometry of oximes was affected and syn-oximes were cyclized efficiently. However, it was found that the anti-oxime is not suitable for the cyclization.     

超顺磁性介孔纳米颗粒嫁接肟Pd环络合物对Heck反应的催化活性

采用溶胶-凝胶法制备出介孔二氧化硅包裹四氧化三铁纳米复合颗粒,在其表面修饰巯基,并以此为载体通过-SCH2-化学键嫁接长链的肟钯环络合物.利用透射电镜(TEM)、高分辨透射电镜(HRTEM)、傅里叶变换红外(FT-IR)光谱、N2吸附-脱附、X光电子能谱(XPS)、振动样品磁强计(VSM)等手段对催化剂进行表征,通过Heck反应对催化剂的活性进行评价.实验结果表明:所制备的磁性颗粒直径约为150nm,比表面积为287.0m2·g-1,且具有大小为3.5nm呈不规则的孔道结构,整个催化剂呈现超顺磁性.对于碘代苯与丙烯酸乙酯之间的Heck反应,2.5h后碘代苯的转化率可达到99%,催化剂在重复使用6次后能保持很高的催化活性(碘代苯转化率为95%).催化剂可稳定分散于反应体系中,并可在外磁场作用下快速与反应体系分离.