Pd/NbOPO4 Multifunctional Catalyst for the Direct Production of Liquid Alkanes from Aldol Adducts of Furans

Great efforts have been made to convert renewable biomass into transportation fuels. Herein, we report the novel properties of NbO_x‐based catalysts in the hydrodeoxygenation of furan‐derived adducts to liquid alkanes. Excellent activity and stability were observed with almost no decrease in octane yield (>90 % throughout) in a 256 h time‐on‐stream test. Experimental and theoretical studies showed that NbO_x species play the key role in C? O bond cleavage. As a multifunctional catalyst, Pd/NbOPO₄ plays three roles in the conversion of aldol adducts into alkanes: 1) The noble metal (in this case Pd) is the active center for hydrogenation; 2) NbO_x species help to cleave the C? O bond, especially of the tetrahydrofuran ring; and 3) a niobium‐based solid acid catalyzes the dehydration, thus enabling the quantitative conversion of furan‐derived adducts into alkanes under mild conditions.     

Directed Aldol Condensations

The present article describes the discovery of a new procedure for aldol condensations for the preparation of α,β-unsaturated carbonyl compounds

1 G. Wittig, H. Pommer, and W. Stilz, German Patent 1199252 (April 5, 1963), BASF; Chem. Abstr. 63, P 1739c (1965).

. The scope of this process is demonstrated by many examples, including some from the natural products sector; at the same time, however, these examples also mark its limitations. The metalated Schiff's bases may be classified as ambident anions; this also explains acylations on the nitrogen. A comparison of the new directed aldol condensation with the formation of unsaturated carbonyl compounds through olefination via phosphorylids shows that the latter method fails when a ketone is used as the substrate. This is where the described procedure using metalated Schiff's bases proves its value.     

Synthesis of Thione-Propiolic Acid Adducts

Abstract

Reaction of adamantane-2-thione with propiolic acid gave a novel type of cycloadducts, spiro[adamantane-2,2′-(1,3)-oxathiin]6-one, quantitatively. Thiocamphor and thiofenchone also reacted with propiolic acid to give the corresponding adducts stereoselectively. The observation of second-order reaction kinetics and highly stereoselective addition strongly support a cycloaddition mechanism for the thermal addition. The reaction of selenoketones with propiolic acid afforded a similar cylcoadduct. This is the first example of the reaction of monomeric thiones or selones with acetylenic acids.     

Gas-Chromatographic Analysis of Terpenoid-Maleic Adducts

Conditions were found for separation of a mixture of terpenoid-maleic adducts and maleic adduct of resin acids in the form of methyl esters by gas-liquid chromatography.     

Stereoselectivity in the Triose Aldol Condensation and the Aldol Condensation Between Glyceraldehyde and Glycolaldehyde

Abstract

Hydroxides of various alkali and alkaline earth metals have been investigated as catalysts in the triose aldol condensation and the aldol condensation between glyceraldehyde and glycolaldehyde. The proportions of diastereomers are very similar in the different product mixtures. Mechanistic models, previously suggested for other aldol condensations, have been considered for the reaction, and the observed diastereoselectivity is in accordance with a pericyclic transition state formed from a cis-enediolate-attack on the aldehyde.     

Aldol Condensation of Acetylferrocene under Ultrasound

Aldol condensation of acetylferrocene with aromatic aldehydes afforded ferroceny-lenones in 76%-92% yields under ultrasound at room temperature.     

The Catalytic Asymmetric Aldol Reaction

The construction of C-C bonds with complete control of the stereochemical course of a reaction is of utmost importance for organic synthesis. The aldol reaction-the simple addition of an enolate donor to a carbonyl acceptor-is one of the most powerful reactions available to the synthetic chemist. In general, control of the relative and absolute configuration of the newly formed stereogenic centers has been achieved through the use of chiral starting materials or chiral auxiliaries. In recent years the search for catalytic methods that efficiently and effectively transfer chirality information has become a major effort in synthetic organic chemistry. Two different approaches have been taken toward the catalytic asymmetric aldol reaction: biocatalysis and catalysis with small molecules. Both approaches have specific advantages and limitations, and as a result are complementary to each other. The important efforts toward both approaches are reviewed in this article.     

Chiral N-Acetyl Selone-Promoted Aldol Reactions

The chiral oxazolidineselone functionality was found to be an excellent partner in the stereospecific acetate aldol reaction with aldehydes via the titanium enolates. Good stereocontrol was obtained as determined by NMR spectroscopy. The oxazolidineselone also provided a straightforward way to establish the stereopurity of the coupling reaction through ⁷⁷Se NMR spectroscopy.     

Aldol reactions of a cyclobutanone enolate

Addition of an aldehyde and zinc chloride to a cyclobutanone enolate, prepared by the reaction of an α-chlorocyclobutanone with dimethylcopperlithium, gave an aldol adduct in good yield.     

A Designed Amide as an Aldol Donor in the Direct Catalytic Asymmetric Aldol Reaction

The direct catalytic asymmetric aldol reaction offers efficient access to β‐hydroxy carbonyl entities. Described is a robust direct catalytic asymmetric aldol reaction of α‐sulfanyl 7‐azaindolinylamide, thus affording both aromatic and aliphatic β‐hydroxy amides with high ee values. The design of this transformation features a cooperative interplay of a soft and a hard Lewis acid, which together facilitate the challenging chemoselective enolization by a hard Brønsted base.     

Chiral Diamine-catalyzed Asymmetric Aldol Reaction

A highly efficient catalytic system composed of a simple and commercially available chiral primary diamine (1R,2R)-cyclohexane-1,2-diamine(6) and trifluoroacetic acid (TFA) was employed for asymmetric Aldol reaction in em-PrOH at room temperature. A loading of 10%(molar fraction) catalyst 6 with TFA as a cocatalyst could catalyze the Aldol reactions of various ketones or aldehydes with a series of aromatic aldehydes, furnishing Aldol pro- ducts in moderate to high yields(up to >99%) with enantioselectivities of up to >99% and diastereoselectivities of up to 99:1.     

Pyridine Adducts of Tricyano- and Dicyanoboranes

Cyanoborane adducts of the Lewis acids B(CN)₃, BF(CN)₂, and BH(CN)₂ with pyridine and 4-cyanopyridine have been obtained in high yields. The syntheses were accomplished by oxidation of the readily available potassium salts of the cyano(hydrido)borate anions [BH(CN)₃]⁻ ( MHB ), [BFH(CN)₂]⁻ ( FHB ), and [BH₂(CN)₂]⁻ ( DHB ) with bromine in the presence of the respective pyridine derivative C₅H₅N or 4-CN-C₅H₄N as starting material. All six cyanoborane adducts have been characterized by NMR and vibrational spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The reduction of the cyanoborane adducts has been investigated by cyclic voltammetry and the Lewis acidity of the different cyanoboranes has been assessed using the Gutmann-Beckett method. Selected experimental data and trends are compared to theoretical ones, for example fluoride ion affinities (FIAs).     

Quantum-Chemical Study of Adducts of Silicon Halides with Nitrogen-containing Donors: IV. Adducts with Pyridine

The structural and thermodynamic characteristics of SiX₄·Py and SiX₄·2Py adducts (X = H, F, Cl, Br) were calculated by ab initio and DFT methods (RHF and B3LYP). The resulting data were used to estimate for the first time the enthalpies of sublimation of trans-SiX₄·2Py complexes. The distortion energies of the donor and acceptor fragments and the energies of the Si-N bonds in the 1:1 and 1:2 halide complexes were calculated. The high distortion energy makes thermodynamically unfavorable equatorial monopyridine adducts with Si-N bond energies of 150-200 kJ/mol. In trans 1:2 complexes, pyridine acts as a weaker donor than ammonia with respect to silicon tetrahalides.     

DNA加合物检测

DNA加合物是一类极其重要的、具有多种标志作用的生物标志物,可应用于环境致癌物的暴露监测、基因毒性测定、个体敏感性和环境致癌物与基因的相互作用研究、癌症风险评价、环境致癌因素筛查以及癌症预防研究等.可靠、灵敏、准确的分析检测技术是DNA加合物作为生物标志物得到广泛应用的关键.当前DNA加合物分析、检测的方法主要包括:32P后标记法、免疫分析法、免疫毛细管电泳激光诱导荧光法、液相色谱串联质谱法、微分离.质谱联用法等.本文对这些分析技术和方法及其在DNA加合物检测方面的应用做一简要综述.