Search results for "cycle"
showing 10 items of 3119 documents
Crystal structure of (E)-4-methoxy-2-{[(5-methylpyridin-2-yl)imino]methyl}phenol
2015
The molecule of the title Schiff base compound, C14H14N2O2, displays anEconformation with respect the imine C=N double bond. The molecule is approximately planar, with the dihedral angle formed by the planes of the pyridine and benzene rings being 5.72 (6)°. There is an intramolecular hydrogen bond involving the phenolic H and imine N atoms.
Mo-Based Oxidizers as Powerful Tools for the Synthesis of Thia- and Selenaheterocycles.
2019
A highly efficient synthetic protocol for the synthesis of thia- and selenaheterocycles has been developed. By employing a MoCl5 -mediated intramolecular dehydrogenative coupling reaction, a broad variety of structural motifs was isolated in yields up to 94 %. The electrophilic key transformation is tolerated by several labile moieties like halides and tertiary alkyl groups. Due to the use of disulfide or diselenide precursors, a high atom efficiency was achieved.
Synthesis of 4-amino-5-fluoropyrimidines and 5-amino-4-fluoropyrazoles from a β-fluoroenolate salt
2020
A synthesis of fluorinated pyrimidines under mild conditions from amidine hydrochlorides and the recently described potassium 2-cyano-2-fluoroethenolate was developed. A broad substrate scope was tested and mostly excellent yields were obtained. The synthesis of fluorinated aminopyrazoles from the same fluorinated precursor could be demonstrated but proceeded with lower efficiency.
Inhibition of Plant Lactate Dehydrogenase Isoenzymes by Benzoic Acid and Cinnamic Acid Derivatives
1976
Summary Several phenolic compounds such as derivatives of benzoic and cinnamic acid were investigated with respect to their inhibitory effect on potato tuber lactate dehydrogenase isoenzymes. Ki values were determined and it was found that they were in the range of 10−2 M for several benzoic acid derivatives while they were in the range of 10−5 M for several hydroxylated cinnamic acid derivatives such as 3,4-dihydroxy cinnamic acid, p(m)nitrocinnamic acid, and 7,8-dihydroxy-4-methyl coumarin as well as kynurenic acid. Also coumaric acid derivatives revealed a very strong inhibition: The K1 values for coumarin and p-coumaric acid were in the range of 10−4 M. The inhibition by all aromatic co…
Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs
2012
Studies of the living organic matter humification process are essential for understanding the carbon biogeochemical cycle. The aim of this study is to analyze relations between the properties of peat, peat humic acids and peat humification degree. The analysis has been done on samples of humic substances extracted from peat profiles in two ombrotrophic bogs and relations between peat age, decomposition and humification degree, botanical composition and properties of peat humic acids (elemental, functional composition) were studied. The found variability of peat properties is less significant than differences in the properties of peat-forming living matter, thus revealing the dominant impact…
Genesis of Peat Humic Acid Structure and Properties Within Bog Profiles
2012
Studies of living organic matter humification process are essential for understanding of carbon biogeochemical cycle, and considering this, the aim of this study is to analyse relations between properties of the peat, peat humic acids (HAs) and humification degree on example of analysis of two bog profiles in ombrotrophic bogs to identify the links between peat age, decomposition and humification degree, botanical composition and properties of peat humic acids (elemental, functional composition). The found variability of peat properties is much less than the significant differences in properties of peat-forming living matter, thus stressing the dominant impact of humification process on pea…
Base-Dependent Stereodivergent Intramolecular Aza-Michael Reaction: Asymmetric Synthesis of 1,3-Disubstituted Isoindolines
2013
The nucleophilic addition (A(N)) / intramolecular aza-Michael reaction (IMAMR) process on Ellman's tert-butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3-disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza-Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C2-symmetric bisacetate-substituted isoindolines. In addition, bisacetate isoindolines bearing two well-differentiated ester moieties are also noteworthy because they may a…
An Insight into Substrate-Dependent Fluorination of some Highly Substituted Alicyclic Scaffolds
2017
The substrate-dependent fluorination of some highly-functionalized cyclopentane derivatives with multiple chiral centers has been investigated. The key steps of the stereocontrolled syntheses are the oxidative cleavage of the ring carbon–carbon double bond of readily available diexo or diendo norbornene β-amino acid derivatives followed by transformation of the resulted dialdehyde stereoisomers by reduction. Finally, substrate-directable chemodifferentiation of different types of hydroxy groups under fluorination procedures gave various densely functionalized alicyclic derivatives or heterocycles.
Selective recognition of aromatic hydrocarbons by endo-functionalized molecular tubes via C/N-H⋅⋅⋅π interactions
2018
Abstract Molecular recognition of aromatic hydrocarbons by four endo -functionalized molecular tubes has been studied by 1 H NMR spectroscopy, computational methods, and single crystal X-ray crystallography. The binding selectivity is rationalized by invoking shape complementarity and dipole alignment. The non-covalent interactions are proved to predominantly be C/N-H⋅⋅⋅ π interactions.
Traceless chirality transfer from a norbornene β-amino acid to pyrimido[2,1-a]isoindole enantiomers
2017
Abstract The synthesis of two enantiomeric pairs of pyrimidoisoindoles 9a, 9b and 10a, 10b is reported. During a domino ring-closure reaction, followed by cycloreversion, the chirality of diendo-(−)-(1R,2S,3R,4S)-3-aminobicyclo[2.2.1]hept-5-ene-2-carboxamide [(−)-1] was successfully transfered to heterocycles (+)-9a, (+)-10a, (−)-9b, (−)-10b and (−)-10c.