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71.
Zijp EJ van der Vlugt JI Tooke DM Spek AL Vogt D 《Dalton transactions (Cambridge, England : 2003)》2005,(3):512-517
Chiral aminophosphines Ph2PN(R)(CH2)nN(R)PPh2 1-4 [n= 2, R = CH(CH3)(Ph) 1; n= 3, R = CH(CH2CH3)(Ph) 2, n= 2, R = CH(CH3)(1-naphthyl) 3; n= 2, R = CH(CH3)(C6H11) 4] were synthesized by the reaction of ClPPh2 with the appropriate easily accessible enantiopure amine building blocks. For compounds 1 and 2, the corresponding selenides 5 and 6 were prepared to determine the electronic character of the phosphine moieties. By reaction of 1 with either PdCl2(cod) or PdCl(CH3)(cod) the cis-complexes 7 and 8 were obtained. The molecular structure for complex 7, cis-[PdCl2(1)], was determined by X-ray crystallography. Reaction of PtCl2(cod) with 1 or 2 yielded the corresponding monomeric cis-isomers 9 and 10. The rhodium derivative [RhCl(CO)(1)] (11) was obtained as a mixture of cis and trans-isomers. Preliminary results in the rhodium catalyzed hydroformylation of styrene and vinyl acetate, with ee's up to 51% and high regioselectivities, showed the potential of these chiral aminophosphines for homogeneous catalysis. 相似文献
72.
Treatment of transition-metal—ammonia complexes with ketones yields complexes with RR′CNH ligands. Of particular interest is the stabilization of dialkylketimines such as e.g. (CH3)2CNH and C6H10NH in [M(CO)5{NHC(CH3)2}] or [M(CO)5 {NHC6H10}] (M = Cr, Mo, W). The principle of synthesis may be applied to a wide range of different metals and types of complexes, as can be shown by the synthesis of [C5H5Mn(CO)2 {NHC(CH3)2}], [C5H5Fe(CO)2{NHC(CH3)2}]PF6, [M(CO)4L2] (M = Cr, Mo, W; L = (CH3)2CNH, C6H10NH) and [W(CO)3(diphos){NHC(CH3)}2]. Treatment of [Cr(CO)5NH3] with urotropine gives [Cr(CO)5 {N4(CH2)6}] which is also obtained from [Cr(CO)5THF] and urotropine. The methods of preparation, reactions and spectroscopic properties of the complexes are reported. 相似文献
73.
The 13C-NMR spectra of the synthetic membrane modifying nonadecapeptide Boc-(Aib-l-Ala)5-Gly-Ala-Aib-Pro-Ala- Aib-Aib-Glu(OBz)-Gln-OMe (Aib = α-aminoisobutyric acid), and of synthetic intermediates were used for conformational analysis in solution. The assignments of the 13C-NMR signals of Aib are based on the magnetic nonequivalence (MNE) of the geminal Cβ-signals in asymmetric environment resulting in a shift difference of 0.2–0.5 ppm due to neighbouring chiral residues. More than 4 ppm MNE are observed due to α-helical conformation and about 2.5 ppm for Aib situated in the corners of a rigid β-turn. The Ala-Cα signal is also sensitive to different secondary structures. The Cα signal for C-terminal alanine is found at 49–50 ppm, and for alanine within unordered oligopeptides it absorbs at 50–51 ppm. α-Helical environment shifts the Ala-Cα signal to lower field down to 54 ppm. In methanolic solution the nonadecapeptide shows a α-helical N-terminal region. For the C-terminus beginning with proline-14 no periodically ordered conformation is observed, and we suggest a sequence of β-turns. Furthermore the typical E/Z isomerism of the prolyl-peptide bond can be observed on proline itself and on its neighbour alanine. 相似文献
74.
Preparation of 1,2-Diarylethylenediamines by Aminative Reductive Coupling of Aromatic Aldehydes with Low-Valent Titanium Reagents In a novel McMurry- Type one-pot reaction, aromatic aldehydes and secondary amines are poupled of give the N, N, N′, N′-tetraalkyl-1,2-diarylethylendiamines 1–22 (Table 3). To this end, a lithium dialkylamide is added to an aromatic aldehyde to give the adduct B which is then treated with 1 equiv. of TiC14 to yield a coloured suspension of a reagent synthetically equivalent to a iminium salt ( C/D in Scheme 4). After treatment with a low-valent Ti reagent which is prepared by reduction of TiC14 with either K or, preferably, Mg, the coupling products are isolated in 23 to 81% yield as a 1:1 mixture of the diastereoisomers (meso- and rac-form). These are separated either by chromatography or by crystallization and characterized. 相似文献
75.
Sabine Strohschein Matthias Pursch Heidrun Händel K. Albert 《Analytical and bioanalytical chemistry》1997,357(5):498-502
The separation of cis/trans isomers of β-carotene has been performed with a C30 stationary phase employing 1H NMR spectroscopy as an on-line detection technique. 1D as well as 2D NMR spectra have been recorded in the stopped-flow
mode for the predominant chromatographic peaks. Structural assignment of the five identified isomers was performed via comparison
of simulated 1D 1H NMR spectra on the basis of the structures of β-carotene cis/trans isomers with the experimental data, and also by the analysis of the proton-proton connectivities in the 2D NMR spectra of
three isomers with the highest concentration. The chromatographic retention behaviour of the isomers agreed well with previously
reported data. The advantage of the applied hyphenated coupling technique compared to conventional off-line techniques lies
in the fact that chromatographic separation and NMR detection are performed in a closed system, so that reisomerization of
the separated compounds is inhibited.
Received: 29 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996 相似文献
76.
Dieter Seebach Stefan G. Müller Urs Gysel Jürg Zimmermann 《Helvetica chimica acta》1988,71(5):1303-1318
Preparative Chromatographic Resolution of Synthetically Useful Cyclic Acetals Racemic cyclic acetals derived from aldehydes and glycine, glycolic acid, thioglycolic acid, formylacetic acid, and acetoacetic acid (oxazolidinones 4 – 13 , dioxolanones 14 , 15 , oxathiolanone 16 , dioxinones 17 – 23 ) are resolved by preparative high-pressure liquid chromatography on silica gel coated with the polymer from N-acryloylphenylalanine ethyl ester (Chiraspher®). The separation factors α range from1,1 to 2,4. Use of a Prepbar®-chromatography system allows injection of several grams at a time. The enantiomeric acetals thus obtained are fully characterized. First application to amino-acid synthesis are mentioned. 相似文献
77.
Guido Kickelbick Dieter Rutzinger Thomas Gallauner 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1157-1164
Summary. Hexadentate ligands were formed by the reaction of primary dimethylaminoethyl- or methoxyethylamines with formaldehyde. The
resulting N, N′, N″-functionalized hexahydro-1,3,5-triazines contain pending amino or ether functionalities which are able to coordinate to
metals in addition to the ring nitrogen atoms. Both ligands were reacted with CuBr, and novel tricopper clusters were isolated
and characterized by X-ray structure analysis. In these compounds a ring nitrogen atom, the pending amino or ether functionality,
and two bridging bromine atoms coordinate each of the copper atoms.
Received January 22, 2002; accepted (revised) March 22, 2002 相似文献
78.
Perfluoroalkyl iodine compounds: preparations and properties of CF3IO, CF3IOF2, and CF3IO2. The trifluoromethyl iodine compounds CF3IO, CF3IOF2, and CF3IO2 are formed from the reactions of CF3I, CF3IF2 or CF3IF4 with ozone or silicon dioxide respectively. Their preparartions, properties, 19F-nmr spectra, and ir spectra are described. 相似文献
79.
Dieter Seebach Laurent Schaeffer Franois Gessier Pascal Bindschdler Corinna Jger Delphine Josien Sascha Kopp Grald Lelais YogeshR. Mahajan Peter Micuch Radovan Sebesta BerndW. Schweizer 《Helvetica chimica acta》2003,86(6):1852-1861
Multigram amounts of suitably protected β2‐amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones (acyl‐DIOZ; 1 ) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55–90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2 – 8 thus obtained are converted to protected β2‐amino acids by standard procedures (Table 1). Many of the DIOZ derivatives are highly crystalline compounds (31 X‐ray crystal structures in Table 2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield. 相似文献
80.
Duma L Hediger S Brutscher B Böckmann A Emsley L 《Journal of the American Chemical Society》2003,125(39):11816-11817
We show that the resolution of homonuclear multidimensional solid-state NMR correlation experiments can be significantly improved using transition selection and spin-state-selective polarization transfer techniques. The selection and transfer of single states allow the removal of the J-coupling contribution from the line width in both the direct and indirect spectral dimensions. This is demonstrated with a new spin-state-selective CO-Calpha correlation experiment, applied to a microcrystalline 85-residue protein. With this new sequence, all four components of the CO-Calpha cross-peaks are separated into different spectra, obtained by linear combination of four recorded data sets. Line narrowing of up to 44% was obtained on the protein sample for the spin-state-selective CO-Calpha spectrum compared to a standard spin-diffusion experiment. The new technique also allows an easy distinction between "direct" and "relayed" transfer cross-peaks. 相似文献