Search results for "organo"
showing 10 items of 1460 documents
ChemInform Abstract: Stereoselective Synthesis of α-Arylalkylamines by Glycosylation-Induced Asymmetric Addition of Organometallic Compounds to Imine…
2009
Arylalkylamines are of interest as building blocks for the synthesis of biologically active compounds and as chiral ligands or chiral auxiliaries in stereoselective syntheses [1]. Their stereoselective synthesis has been achieved by enantioselective reduction of ketimines using chiral reagents [2], as for example Corey’s oxaborolidines [3], or proline-derived triacyloxyborohydrides [4]. Particularly efficient asymmetric syntheses of chiral arylalkylamines have been accomplished by Noyori et al. [5] through enantioselective catalysis of hydrogen transfer reactions using a chiral 1,2-diphenyl-ethylenediamine ruthenium catalyst. Enantioselective transferhydrogenationshave also been achieved us…
Stereoselective Synthesis of α-Arylalkylamines by Glycosylation-induced Asymmetric Addition of Organometallic Compounds to Imines
2009
Arylalkylamines are of interest as building blocks for the synthesis of biologically active compounds and as chiral ligands or chiral auxiliaries in stereoselective syntheses [1]. Their stereoselective synthesis has been achieved by enantioselective reduction of ketimines using chiral reagents [2], as for example Corey’s oxaborolidines [3], or proline-derived triacyloxyborohydrides [4]. Particularly efficient asymmetric syntheses of chiral arylalkylamines have been accomplished by Noyori et al. [5] through enantioselective catalysis of hydrogen transfer reactions using a chiral 1,2-diphenyl-ethylenediamine ruthenium catalyst. Enantioselective transferhydrogenationshave also been achieved us…
Mukaiyama–Michael Reactions with trans-2,5-Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent Interactions, Not from …
2013
The scope of the enantioselective Mukaiyama-Michael reactions catalyzed by trans-2,5-diphenylpyrrolidine has been expanded to include both α- and β-substituted enals. However, the rationalization of the observed enantioselectivity is far from obvious since the catalyst is not very sterically hindered. DFT calculations were carried out to rationalize the observed stereoselectivities. Transition states of the C-C bond formation between iminium intermediates and silyloxyfurans were located and their relative energies were used to estimate the stereoselectivity data. We find excellent agreement between the predicted and observed stereoselectivities. The analysis of intermolecular forces reveals…
ChemInform Abstract: Microwave-Assisted Tandem Organocatalytic Peptide-Coupling Intramolecular aza-Michael Reaction: α,β-Unsaturated N-Acyl Pyrazoles…
2015
Conjugated N-acyl pyrazoles are successfully employed in the organocatalytic enantioselective intramolecular aza-Michael reaction as ester surrogates.
Analysis of odour and taste problems in high-density polyethene
1998
Abstract The compounds that cause off-flavours in plastics, have been recognized mainly as carbonyl compounds (aldehydes, ketones and esters). They occur in low concentrations, and due to their low-threshold odour concentrations, their typical odours were identified. Most of these off-flavour compounds are volatile. Chemical analysis of smelling compounds requires a very sensitive method with a high-resolution capability. The analysis of volatile organic compounds (VOCs) in high density polyethene (HD-PE) granules and waters in which the granules have been shaken for 4 h, were carried out by gas chromatography–mass spectrometry–sniffing system (GC–MS–SNIFF) and by gas chromatography–fourier…
Effects of organoclay on morphology and properties of nanocomposites based on LDPE/PA-6 blends without and with SEBS-g-MA compatibilizer
2009
LDPE/PA-6 blends (75/25 wt/wt) were added with SEBS-g-MA (S) and/or an organoclay (20A) using different compounding sequences and the morphology and the properties of the blends or composites were investigated. An XRD study of the nanocomposites with pure polymers showed that 20A is intercalated by LDPE or PA-6 chains, whereas it is exfoliated by S if the clay concentration does not exceed 10 wt%. The SEM investigation showed that both S and 20A behave as efficient emulsifying agents for the LDPE/PA-6 blends. However, their effect on the mechanical properties was found to be opposite: S enhanced toughness but lowered the stiffness, whereas 20A improved the elastic modulus but impaired the i…
Theoretical characterization of the electronic structure of polymeric systems combining disilanylene and /spl pi/-conjugated units
1994
Summary form only given. Polymeric organosilicon systems are in the forefront of research, due to their intriguing properties (semiconducting behavior, photoconduction, non-linear optical properties, and thermo- and piezochromism). The fundamental skeletons of most of these polymers consist of a /spl sigma/-electron network formed by silicon-silicon bonds. Recently, polymeric organosilicon systems containing a regular alternation of a disilanylene unit and carbon /spl pi/-conjugated moiety as phenylene, ethynylene, or ethenylene have been synthesized. The purpose of this contribution is to perform a detailed study of the electronic structure of polymers containing alternated disilanylene an…
Formation of arynezirconocenes from substituted diaryl bis (t-butylcyclopentadienyl) zirconium: application to the synthesis of new functionalizedort…
1991
The para-substituted diphenylzirconocenes [(t-BuCp)2Zr(p-C6H4R)2; R = Br, NMe2] (A) were easily obtained from the reaction of the appropriate organolithium reagent with bis(t-butylcyclopentadienyl)zirconium dichloride. Elimination of bromobenzene or N,N-dimethylaminobenzene from A by slight heating led to arynezirconocenes into which were inserted two equivalents of elementary chalcogens. As a result dichalcogenated zirconacycles [(t-BuCp)2ZrY2C6H3R; Y = S, Se] (B) were obtained. Complexes B constitute useful potential synthons in organic synthesis and a large family of new functionalized dichalcogenated benzenic compounds was prepared by reacting electrophiles. The structure of complexes B…
Effects of Gibberellic Acid on Morphogenesis and Cardenolide Accumulation in Juvenile and Adult Digitalis obscura Cultures
1993
Summary Effects of gibberellic acid on morphogenesis and cardenolide accumulation in in vitro cultures of Digitalis obscura are reported. Cultures were established from hypocotyls or leaves of axenic seedlings and shoot tips of mature plants. Irrespective of the kind of explant, gibberellic acid by itself did not induce morphogenesis but modified those morphogenic responses promoted by auxins and/or cytokinins, always inhibited organogenesis and favoured both embryo formation and conversion into plants. Gibberellic acid did not significantly affect cardenolide content of plants regenerated from juvenile or mature D. obscura explants.
Morphogenesis in Root Tip Meristem Cultures of Digitalis obscura L.
1987
Summary The morphogenic capacity of Digitalis obscura L. root tip meristems cultured in vitro has been studied, noting hormonal factors inducing differentiation and development of shoots as well as those promoting somatic embryogenesis. Caulogenesis was obtained with different auxin/cytokinin combinations but a high rate of shoot regeneration was induced by 0.1 or 0.5 ppm IAA and 1.0 ppm BA. Different stages of somatic embryo development were observed in media supplemented with auxins or high auxin/cytokinin ratios, although no complete plant regeneration was achieved. This is the first report known of shoot regeneration from root tips of Digitalis obscura L.