syn-2,3-Disubstituted-2,3-dihydro-1,4-benzoxathiin rings: preparation from quinone ketals and 2-mercaptoethanols

A general method for the preparation of syn-2,3-disubstituted-2,3-dihydro-1,4-benzoxathiin rings from 2-mercaptoethanols and quinone ketals is presented. This ring system is produced by Michael addition of a 2-mercaptoethanol to a quinone ketal, followed by cyclization of the initial Michael adduct, and subsequent aromatization to afford a syn-2,3-disubstituted-1,4-benzoxathiin in fair to good chemical yield. Several chiral syn-2,3-disubstituted-2,3-dihydro-1,4-benzoxathiin rings were prepared with this method from enantioenriched 2-mercaptoethanols. No loss of enantiopurity was observed.     

Kinetic studies of nickel speciation in model solutions of a well-characterized humic acid using the competing ligand exchange method

Publications on the binding characteristics of metals with humic acid (HA) are sparse. Here we investigated the release of nickel from Ni(II)-HA complexes using model solutions of three different [Ni(II)]/[HA] mole ratios at three different pH values; we also compared the results with those of [Ni(II)]/[FA] complexes from previous work in this laboratory. Ligand exchange kinetics using the competing ligand exchange method (CLEM) were studied using two different techniques: graphite furnace atomic absorption spectrometry (GFAAS) with Chelex 100 resin as the competing ligand, and adsorptive cathodic stripping voltammetry (AdCSV) with dimethylglyoxime as the competing ligand to measure the rate of dissociation of Ni(II)-HA complexes. The results of the kinetic studies showed that as the [Ni(II)]/[HA] mole ratio was decreased, the rate of dissociation of Ni(II)-HA complexes decreased, and the proportion of free Ni²⁺ ions plus very labile nickel complexes decreased while the proportion of the less labile kinetically distinguishable components increased. Generally, the rate of dissociation of Ni(II)-HA complexes was slower than that of Ni(II)-FA complexes. Studies on the validity of the kinetic model showed that the concentrations of chemical species varied in a reasonable way with pH and the [Ni(II)]/[HA] mole ratios, indicating that the kinetically distinguishable components have chemical significance and the kinetic model is valid.     

Dirhodium(II)-catalyzed carbonyl ylide generation. Stereoelectronic control in dioxolane formation

The combination of ethyl diazoacetate with aryl aldehydes in the presence of copper(I) or rhodium(II) catalysts results in the formation of 1,3-dioxolane products in moderate to good yields. These reactions occur through a pathway that involves ylide intermediates. Catalyst-dependent diastereocontrol is observed and suggests that metal-associated ylides are involved in the product-determining step. The influence of aryl aldehyde substituents has been determined. Current address. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 961–965, May, 1998.     

Synthesis of Functionalized (2-Thienylcarbonyl)thiazoles and 4-(2-Thienyl)pyridines by Reaction of (2-Thienylcarbonyl)thioacetanilides and their Enamine Derivatives

Summary. The condensation of two molecules of 2-(2-thienylcarbonyl)thioacetanilides catalyzed by piperidine yielded thiazole derivatives as confirmed by X-ray crystal structure analysis. The reaction of malononitrile with 3-morpholino-3-(2-thienyl)acrylic acid thioanilides furnished 6-amino-1-aryl-4-(2-thienyl)-1,2-dihydro-2-thioxopyridine-5-carbonitriles. A similar reaction of malononitrile with 3-morpholino-3-(2-thienyl)acrylic acid anilides provided 2-oxopyridine-5-carbonitriles.     

Rapid biomass analysis

New, rapid, and inexpensive methods that monitor the chemical composition of corn stover and corn stover-derived samples are a key element to enabling the commercialization of processes that convert stover to fuels and chemicals. These new techniques combine near infrared (NIR) spectroscopy and projection to latent structures (PLS) multivariate analysis to allow the compositional analysis of hundreds of samples in 1 d at a cost of about $10 each. The new NIR/PLS rapid analysis methods can also be used to support a variety of research projects that would have been too costly to pursue by traditional methods.     

α-(1H-1,2,4-三唑-1-基)-β-芳硫基取代苯酮的合成及生物活性研究

利用 2 (1H 1,2 ,4 三唑 1 基 ) 2 丙烯 1 酮 (2 )与取代硫酚或含巯基的杂环化合物进行 1,4 亲核加成 ,得到目标化合物 3,其结构经元素分析、核磁和红外光谱所证实 ,并对其进行了生物活性的测试 ,发现大部分化合物具有很好的抑菌活性 .结构与活性的关系表明不同的R1取代对其生物活性有较大的影响 ,当R1=(CH3 ) 3 C时 ,对小麦锈病的抑制活性要高于R1=Ar的活性 ,而Ar上不同的取代基对其活性影响不大     

Pyridazine derivatives. Part 40: Reactivity of 5-alkynylpyridazin-3(2H)-ones toward hydrochloric acid

5-Alkynylpyridazin-3(2H)-ones or 5-(2-chloroalkenyl)pyridazin-3(2H)-ones were isolated during the cleavage of the methoxymethyl group in a series of 5-alkynyl-2-methoxymethylpyridazin-3(2H)-ones by treatment with hydrochloric acid. The efficient and selective cleavage of the methoxymethyl group in these compounds can be performed under mild conditions by employing aluminium chloride.     

Synthesis of 1,3-bis(N,N-difluoroamino)adamantane: addition of difluoramino radicals to 1,3-dehydroadamantane

1,3-Dehydroadamantane undergoes a facile reaction with tetrafluorohydrazine to give 1,3-bis(N,N-difluoroamino)adamantane, the product of 1,3-NF₂ radical addition.     

Ab initio study of the ground state and conformational stability of peroxyacetyl nitrate in internal rotation about the peroxide bond

The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998.