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At least 415 records · Page 23Linked to original sources
PubMed2000

Concept of improved rigidity: how to make enantioselective hydrophosphonylation of cyclic imines catalyzed by chiral heterobimetallic lanthanoid complexes almost perfect

The catalytic and enantioselective hydrophosphonylation of cyclic imines using cyclic phosphites is described for the first time. In contrast to the application of acyclic phosphites, significant improvements are presented arising from the concept of improved rigidity by utilization of cyclic phosphites in the lanthanoid BINOL complex catalyzed hydrophosphonylation of 3-thiazolines. Cyclic phosphites are shown to provide certain improvements within the catalytic cycle. Influence of parameters such as concentration of the catalyst and the phosphite on the catalysis is examined as well as the effects of the substituents on the starting material. The pharmacologically interesting thiazolidinyl phosphonates are synthesized in excellent optical purities of up to 99% ee and high chemical yields of up to 99%. The required amount of catalyst is reduced to 2.5 mol %. The highest efficiency of the reaction involving cyclic phosphites is achieved using the catalytic system "2.5 mol % (S)-YbPB/2.5 equiv phosphite/50 degrees C/48 h/THF-toluene (1:7)". On the basis of the results a refinement of the proposed catalytic cycle has been provided. For comparison cyclic phosphites were used in hydrophosphonylation with a chiral titanium catalyst.

Journal Article↗
PubMed2005

Deuterium isotope effects on the interaction between hyperbranched polyethylene imine and an anionic surfactant.

Solvent isotope effects on the interaction between the hyperbranched cationic polyelectrolyte, polyethylene imine (PEI), and the anionic surfactant sodium dodecyl sulfate (SDS) were investigated using potentiometric titration and eletrophoretic mobility measurements. In the basic pH range, a significantly higher fraction of the amine groups was found to be protonated when the PEI was dissolved in D2O compared to H2O at the same pH/pD. The difference in polymer charge in the two solvents decreases gradually with decreasing pH, and it completely diminishes at around pH = 4. Electrophoretic mobility measurements of PEI/SDS complexes at different pH values correlated very well with these observations. At pH/pD approximately 9 a much higher mobility of the PEI/SDS complexes was found in D2O than in H2O at low surfactant concentrations, and the charge neutralization point shifted to a considerably larger surfactant concentration in heavy water. These results can be explained by the significantly higher charge density of the PEI in D2O compared to H2O. However, at the natural pH/pD as well as at pH = 4 and pD = 4 conditions the PEI molecules have roughly equal charge densities, which result in very similar charged characteristics (mobilities) of the PEI/SDS complexes as well as the same charge neutralization SDS concentration. It can be concluded that extreme care must be taken in the general analysis of those experiments in which weak polyelectrolyte/surfactant aggregates are investigated in heavy water, and then these observations are correlated with structures of the same system in water.

Journal Article↗
PubMed2006

Theoretical study of the enol imine <--> enaminone tautomeric equilibrium in organic solvents.

The tautomeric enol imine <--> enaminone (phenol <--> quinone) equilibrium of the 1-hydroxy-2-naphthaldehyde Schiff base (2-phenyliminomethyl-naphthalen-1-ol) was investigated by density functional theory (B3LYP) and ab initio (MP2) methods in the IEF-PCM polarizable continuum dielectric solvent approximation and by a combined ab initio + FEP/MC study by considering an explicit solvent model. Special emphasis was put on the effect of solvation on this equilibrium by using an apolar (CCl4), polar aprotic (CH3CN), and polar protic (CH3OH) solvent. Compared with experimental tautomerization Gibbs free energies, the IEF-PCM/B3LYP calculations apparently overestimate the stability of the quinone form both when the 6-31G(d,p) and the 6-311++G(d,p) basis sets are applied. IEF-PCM/MP2 studies with the above basis sets predict the preference of the aromatic phenol tautomer, in contrast to the experiment in methanol and acetonitrile solvent. Calculation of the total relative free energy as DeltaG(tot) = DeltaE(int)(IEF-PCM/QCISD(T)/6-31G(d)) + DeltaG(solv, FEP/MC) + DeltaG(thermal) provided agreement with the experimental values up to 0.6 kcal/mol in the three solvents, and the predominant tautomer was always correctly predicted. In-solution relevant atomic charges, derived by a fit to the molecular electrostatic potential generated by the IEF-PCM/B3LYP/6-31G(d,p) wave function, show strong dependence on the fitting procedure (CHELPG or RESP) and are fairly insensitive to the chemical nature of the actual solvent. Use of the CHELPG charges in FEP/MC simulations revealed to be superior in comparison with the use of the RESP charge set.

Acetonitriles↗
PubMed1996

2-(methylamino)-5-chlorobenzophenone imine: a novel product formed in base-catalyzed hydrolysis of diazepam.

Diazepam (1), a hypnotic and anxiolytic drug in worldwide use, formed an intermediate product in a mixture of ethanol and sodium hydroxide ([NaOH] > or = 1 M). The intermediate product slowly decomposed to form 2-(methylamino)-5-chlorobenzophenone imine (2) and 2-(methylamino)-5-chlorobenzophenone (3). The amount of 2 formed, relative to that of 3, increased with increasing NaOH concentration. Compound 2, a heretofore unknown derivative of 1, was characterized by high-performance liquid chromatography, ultraviolet-visible absorption, mass, and proton nuclear magnetic resonance spectral analyses.

Benzophenones↗
PubMed2005

Cylindrical micelles of alpha-fluorocarbon-omega-hydrocarbon end-capped poly(N-acylethylene imine)s.

Micelles of ABC block copolymers with varying degrees of polymerization of the B block (n) and constant lengths of the A and C blocks were investigated by small-angle X-ray scattering (SAXS), analytical ultracentrifugation (AUC), surface tension measurements, and isothermal titration calorimetry. The copolymers consisting of hydrophilic poly(N-acylethylene imine)s, end-capped with a hydrophobic fluorocarbon and a hydrocarbon block, are polymeric surfactants (gamma = 35 mN/m). They form cylindrical micelles with radii of 3.0 nm (n = 35), 3.8 nm (n = 57), and 4.0 nm (n = 72). Their lengths are about 20 nm. The micelles can be doped with 1,4-diiodoperfluorobutane for the polymers with n = 57 and 72 but not for n = 35. We assume that the doped micelles form distinct fluorocarbon domains, which are able to incorporate selectively the fluorocarbon dopant. The work presented here is a contribution to the development of multicompartment micelles.

Fluorocarbons↗
PubMed2006

Maghemite nanoparticles protectively coated with poly(ethylene imine) and poly(ethylene oxide)-block-poly(glutamic acid).

Superparamagnetic iron oxide particles (SPIO) of maghemite were prepared in aqueous solution and subsequently stabilized with polymers in two layer-by-layer deposition steps. The first layer around the maghemite core is formed by poly(ethylene imine) (PEI), and the second one is formed by poly(ethylene oxide)-block-poly(glutamic acid) (PEO-PGA). The hydrodynamic diameter of the particles increases stepwise from D(h) = 25 nm (parent) via 35 nm (PEI) to 46 nm (PEI plus PEO-PGA) due to stabilization. This is accompanied by a switching of their zeta-potentials from moderately positive (+28 mV) to highly positive (+50 mV) and finally slightly negative (-3 mV). By contrast, the polydispersity indexes of the particles remain constant (ca. 0.15). Mössbauer spectroscopy revealed that the iron oxide, which forms the core of the particles, is only present as Fe(III) in the form of superparamagnetic maghemite nanocrystals. The magnetic domains and the maghemite crystallites were found to be identical with a size of 12.0 +/- 0.5 nm. The coated maghemite nanoparticles were tested to be stable in water and in physiological salt solution for longer than 6 months. In contrast to novel methods for magnetic nanoparticle production, where organic solvents are necessary, the procedure proposed here can dispense with organic solvents. Magnetic resonance imaging (MRI) experiments on living rats indicate that the nanoparticles are useful as an MRI contrast agent.

Animals↗
PubMed2000

B(C(6)F(5))(3)-Catalyzed hydrosilation of imines via silyliminium intermediates

A broad range of benzaldimines and ketimines can be hydrosilated efficiently, employing B(C(6)F(5))(3) as a catalyst in conjunction with PhMe(2)SiH. Spectral evidence supports the intermediacy of a silyliminium cation with a hydridoborate counterion formed via abstraction of a hydride from PhMe(2)SiH by B(C(6)F(5))(3) in the presence of imines.

Journal Article↗
PubMed2000

Highly selective aziridination of imines using trimethylsilyldiazomethane and applications of C-silylaziridines in synthesis

Trimethylsilyldiazomethane has been found to add directly to N-sulfonyl (Ts and SES) imines to afford aziridines in good yields and high cis stereoselectivities. The silyl group can be substituted by treatment with a fluoride source and electrophiles again with high selectivity. Complete regioselectivity is observed in ring opening of these aziridines with nucleophiles.

Journal Article↗
PubMed2001

Diastereoselective addition of allylzinc bromide to imines derived from (R)-phenylglycine amide.

The highly diastereoselective addition of allylzinc bromide to imines derived from (R)-phenylglycine amide is reported. Homoallylamines with high enantiomeric purity are obtained from the adducts in three steps on removal of the chiral auxiliary by means of a nonreductive protocol. Removal of the auxiliary by hydrogenation leads to the saturated amines, also in high enantiomeric purity. [reaction: see text]

Journal Article↗
PubMed2002

Acid-free aza Diels-Alder reaction of Danishefsky's diene with imines.

[reaction: see text] A highly efficient aza Diels-Alder reaction of Danishefsky's diene with imines was found to occur in methanol in the absence of any acids at room temperature to give corresponding 2-substituted dihydro-4-pyridone derivatives in high yields. This reaction can be also carried out in a three-component one-pot reaction manner. The reaction was found to proceed through a Mannich-type condensation mechanism.

Journal Article↗
PubMed2002

Solid-phase synthesis of polysubstituted piperidines by imino-Diels-Alder cycloaddition of 2-amino-1,3-butadienes with solid-supported imines.

[reaction: see text] The solid-phase imino-Diels-Alder reaction of 2-amino-1,3-butadienes with solid-supported imines is described. The reaction furnishes 4-piperidones and 4-aminopiperidines with high diastereoselectivity and with very good yields and purity after the release from the solid support. The possibility of introducing variations in both cycloaddition partners gives rise to substituted piperidines with up to five elements of diversity.

Journal Article↗
PubMed2003

Application of monodentate secondary phosphine oxides, a new class of chiral ligands, in Ir(i)-catalyzed asymmetric imine hydrogenation.

Secondary phosphine oxides were prepared from R(1)PCl(2) and R(2)MgBr, followed by hydrolysis. They were obtained in an enantiopure form by preparative chiral HPLC. These new monodentate ligands were tested in the iridium-catalyzed hydrogenation of imines at 25 bar. Enantioselectivities up to 76% were obtained at L/Ir = 2. Addition of pyridine (Pyr/Ir = 1:2) raised the ee to 83%. Using pyridine as an additive allowed reduction of the L/Ir ratio to 1 without reduction of ee. [reaction: see text]

Journal Article↗
PubMed2003

Reactions of arylaldehydes and N-sulfonated imines with dimethyl acetylenedicarboxylate catalyzed by nitrogen and phosphine lewis bases.

[reaction: see text] In the reaction of arylaldehydes or N-sulfonated imines (0.5 mmol) with dimethyl acetylenedicarboxylate (DMAD) (0.6 mmol) catalyzed by pyridine or DMAP (20 mol %), we found that (E)-2-aryl-but-2-enedioic acid dimethyl ester 1 or (E)-2-[aryl-(toluene-4-sulfonylimino)methyl]-but-2-enedioic acid dimethyl ester 2 was formed in good yields at 60 degrees C in THF. A plausible mechanism has been proposed.

Journal Article↗