Introduction of heteroatom-based substituents into 1,4-dihydropyridines by means of a halogen-mediated, oxidative protocol: diamination, sulfonylation, sulfinylation, bis-sulfanylation, and halo-phosphonylation processes

The natural tendency of 1,4-dihydropyridines to undergo "biomimetic" oxidation to afford pyridinium salts can be switched off and, through the use of reagents that interact electrophilically with the enamine moiety present in the heterocyclic system, it is possible to promote alternative oxidations. In this way, efficient regio- and stereocontrolled synthetic methods have been developed that lead to diversely substituted di- and tetrahydropyridines. These include iodoazidation, diamination, bis-sulfonamidation, sulfonylation, sulfinylation, thiocyanation, sulfanylation, bis-sulfanylation, and halo-phosphonylation processes.     

Studies on the metal-nuclotide (Co-5′IMP,Co-5′GMP) interaction via mössbauer emission spectroscopy and magnetic susceptibility measurements

By means of⁵⁷Co Mössbauer emission spectroscopy and magnetic susceptibility measurements, the local symmetries and electronic structure of the Co(II) ions in the Co-5IMO and Co-5GMP complexes in the hydrated and dehydrated forms have been determined.     

Mössbauer studies on one-dimensional iron phthalocyanines

Summary Magnetic moments and⁵⁷Fe Mössbauer spectra at room temperature and at liquid nitrogen temperature of polynuclear ligand-bridged iron phthalocyanines, FePcL (L = pyrazine and 4,4-bipyridyl), are reported. The experimental data are in agreement with a pseudo-octahedral environment around the iron(II) cation. Partially oxidized derivatives, FePc(pz)I_0.26 and FePc(bipy)I_1.06 have been synthesized and their⁵⁷Fe Mössbauer spectra and magnetic moments within the same temperature range obtained. Oxidation is shown to be metal centred and the iodine is found to be in I^– form for FePc(pz)_0.26 and as both I^– and I ₃ ^– species for FePc(bipy)I_1.06. While the magnetic moment of FePc(pz) increases upon oxidation, the opposite occurs for FePc(bipy).     

Conjugate addition of organocuprates to chiral bicyclic delta-lactams. Enantioselective synthesis of cis-3,4-disubstituted and 3,4,5-trisubstituted piperidines

[reaction: see text] Chiral nonracemic bicyclic lactam 3, easily accessible by cyclodehydration of (R)-phenylglycinol and racemic methyl 4-formylhexanoate, was converted to the unsaturated lactams 5, which undergo the stereoselective conjugate addition of lower order cyanocuprates to ultimately lead to enantiopure cis-3,4-disubstituted and 3,4,5-trisubstituted piperidines.     

The modulating possibilities of dicarbollide clusters: optimizing the Kharasch catalysts

exo-Cluster dicarbollides substitution has allowed tuning of the E degrees (Ru(II)/Ru(III)) potential to obtain the best-performing Kharasch catalyst. We postulate that this is possible through the to-and-fro electron movement between the boron cluster and the sulfonium moieties.     

Analysis of primary aliphatic short-chain monoamines by LC in water samples

Several derivatization procedures with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) were compared for a rapid analysis of primary aliphatic short-chain monoamines in water samples by HPLC using a LiChorospher analytical separation column (100RP₁₈ mm i.d., 5 μm). Both the solution and the solid-support assisted off-line derivatization on C₁₈ SPE cartridges were inadequate options because of beginning degradation processes of the instable isoindol derivatives during their transfer to the analytical column. This problem was precluded with the on-column or solid-support assisted on-line derivatization. In the last mentioned procedure, the derivatization took place in a Hypersil C₁₈ precolumn ( mm i.d., 30 μm) connected with an additional preconcentration step resulting in better detection limits (0.002-0.040 μg ml⁻¹ requiring only 150 μl of water sample) than in the on-column procedure (0.08-0.16 μg ml⁻¹). The improved sample handling, the better control of parameters affecting reaction rates, the fully automation of this method with only 10 min analysis time for each sample are further advantageous. The potential of the solid-support assisted on-line derivatization was outlined and applied to water samples from several sources. Recovery values near 100% were obtained.     

Ag(I) complexes with alkylidene-bis(2-aminopyrimidines) as building units for discrete metallomacrocyclic frames. A structural and solution study

Alkylidene-bis(2-aminopyrimidines) (pyr2Cx, x = 2-5) are useful ligands to interact with Ag(I) yielding discrete metallocycles. Crystal structures of the [(pyr2C2)Ag(NO3)]2 and [(H-pyr2C4)Ag(NO3)2]2 have been isolated where each macrocyclic moiety interacts with their surroundings through weak interactions, yielding 3D discrete structures, On the other hand, the solution study shows that the equilibrium constants for the formation of Ag(pyr2Cx)+ complexes are higher than the literature values for Ag(I) complexes with single pyrimidines, although the differences could be explained by invoking the solid-state structures of the Ag(I)-pyr2Cx complexes.     

Effect of asymmetry on the electronic delocalization in diiron and iron-cobalt mixed valence metallocenic compounds

In this work, we report the synthesis and a study on the degree of electronic delocalization in the asymmetric mixed valence complexes [CpFe(C(8)H(6))Fe(C(8)H(7))](+), 3a(+), and [CpCo(C(8)H(6))Fe(C(8)H(7))](+), 3b(+), (Cp = C(5)Me(5), C(8)H(6) = pentalenyde, C(8)H(7) = hydropentalenyde, and = ((3,5(CF(3))(2)C(6)H(3))(4)B(-))). Electrochemical methods, (57)Fe M?ssbauer spectroscopy, electronic spectroscopy, and electron paramagnetic resonance were used for this purpose. Although the anti conformation of the complexes precludes any metal-metal interaction, all the techniques employed show that 3a(+) is a electronic delocalized system, while 3b(+) behaves as two individual metallic centers with localized electron density.