Search results for "Organo"
showing 10 items of 1460 documents
Kāda līdz šim nepazīta cikliska amfībiju dzimumpazīme: vardes priekškāju skeleta sezonu variācijas
1924
Atsevišķs iespiedums no: Latvijas Universitātes Raksti, XI. 1924. Kopsavilkums franču valodā.
Characterization of poly(4-vinylpyridine 1-oxide) by free-solution capillary electrophoresis and micellar electrokinetic chromatography
2008
The migration characteristics of poly(4-vinylpyridine 1-oxide) (PVP-NO) in phosphate buffers of acidic pH (20 mM H 3 PO 4 or NaH 2 PO 4 ) have been studied using both free-solution capillary electrophoresis (FSCE) and MEKC. To inhibit adsorption, 250 mM o-phosphoethanolamine (2-aminoethyl dihydrogen phosphate) was used. In FSCE, PVP-NO showed a narrow peak and a broader band, both having anionic behavior. These peak and band were attributed to the free and aggregated or micellized PVP-NO forms, respectively. According to surface tension measurements, the CMC of SDS in the BGE was 1.8 and 0.48 mM in the absence and in the presence of 1000 μpg/mL PVP-NO, respectively, and the association of t…
New anionic cobalt complexes using highly hindered bis-amides with varying donor abilities as ligands.
2007
Four potential tetradentate ligands of formulae 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)ethane (H(4)L(1), 1), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)propane (H(4)L(2), 2), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)benzene (H(4)L(3), 3) and 1,8-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)naphthalene (H(4)L(4), 4) have been prepared and the crystal structures of three of them (1, 3 and 4) determined by single crystal X-ray diffraction. The investigation of their complexing ability toward Co(II) afforded the compounds of formulae [Co(III)(L(3))Na(I)(H(2)O)(2)] (5), [Co(III)(L(n))Li(I)(H(2)O)2] with n = 1 (6), 2 (7) and 3 (8) and [Co(II)(L(4))Li(I)(2)] (9). Complexes 5-8 are squa…
Dynamic magnetic materials based on the cationic coordination polymer [Cu(btix)2]n(2n+) [btix = 1,4-bis(triazol-1-ylmethyl)benzene]: tuning the struc…
2012
A three-dimensional coordination polymer, [Cu(btix)(2)(BF(4))(2)](n) [btix = 1,4-bis(triazol-1-ylmethyl)benzene], with antiferromagnetic interactions occurring via the organic ligand, has been prepared and characterized. It has been shown to permit the exchange of anionic species in the crystalline network with modification of the magnetic properties. Coordinated BF(4)(-) can be reversibly exchanged by different anions with (NO(3)(-) and Cl(-)) or without (PF(6)(-) and ClO(4)(-)) dynamic response of the organic ligand, which acts as the only linker between the metal centers. Interestingly, an irreversible exchange occurs with N(3)(-) anions to generate a new coordination polymer, [Cu(btix)(…
N-Heterocyclic Carbene-Catalyzed Activation of α-Chloroaldehydes: Asymmetric Synthesis of 5-Cyano-Substituted Dihydropyranones
2017
An N-heterocyclic carbene (NHC)-catalyzed asymmetric [4+2] annulation of (E)-2-benzoyl-3-phenylacrylonitriles with α-chloroaldehydes has been developed. The protocol leads to 5-cyano-substituted dihydropyranones in good to excellent yields with excellent diastereo- and enantioselectivities (up to 93% yield, >20:1 d.r. and 99% ee).
Asymmetric Synthesis of Tetrahydrobenzofurans and Annulated Dihydropyrans via Cooperative One-Pot Organo- and Silver-Catalysis
2016
Synthesis : journal of synthetic organic chemistry 48(19), 3207-3216(2016). doi:10.1055/s-0035-1561468
N‐Heterocyclic Carbene Catalyzed [4+2] Annulation of Enals via a Double Vinylogous Michael Addition: Asymmetric Synthesis of 3,5‐Diaryl Cyclohexenones
2017
A strategy for the N-heterocyclic carbene (NHC) catalyzed asymmetric synthesis of 3,5-diaryl substituted cyclohexenones has been developed via oxidative [4+2] annulation of enals and alkenylisoxazoles. It is the first example of using NHC organocatalysis in a double vinylogous Michael type reaction, a challenging but highly desirable topic. This unprecedented protocol affords good yields as well as high to excellent diastereo- and enantioselectivities.
Organocatalytic Asymmetric Synthesis of Trifluoromethylated Tetrahydrocarbazoles by a Vinylogous Michael/Aldol Formal [4+2] Annulation
2018
N-Heterocyclic Carbene Catalyzed Asymmetric Synthesis of Dihydropyranothiazoles via Azolium Enolate Intermediates
2017
A highly diastereo- and enantiostereoselective synthesis of bicyclic dihydropyranothiazoles combining a thiazole and δ-lactone skeleton via NHC-catalyzed [4+2] annulation of 5-alkenylthiazolones and α-chloroaldehydes has been developed. The heterocyclic products are formed via azolium enolate intermediates in good yields with high diastereo- and enantistereoselectivities.
Switchable Access to Different Spirocyclopentane Oxindoles by N-Heterocyclic Carbene Catalyzed Reactions of Isatin-Derived Enals and N-Sulfonyl Ketim…
2017
A novel NHC-catalyzed annulation protocol for the asymmetric synthesis of biologically important β-lactam fused spirocyclopentane oxindoles with four contiguous stereocenters, including two quaternary carbon centers, was developed. Alternatively, spirocyclopentane oxindoles containing an enaminone moiety can be achieved using the same starting materials, isatin-derived enals, and N-sulfonyl ketimines, in the presence of a slightly different NHC catalytic system. This switchable annulation strategy enables the selective assembly of both heterocyclic scaffolds with good yields and excellent enantioselectivities for a broad range of substrates.