Remote stereocontrol by the sulfinyl group: Mukaiyama aldol reactions of (S)-2-[2-(p-tolylsulfinyl)phenyl]acetaldehyde in the asymmetric synthesis of β-hydroxyacids and 1,3-diols

(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)₃ yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes.     

Stereoselectivity in the intermolecular Pauson-Khand reaction of electron-deficient terminal alkynes

A family of terminal alkyne dicobalthexacarbonyl complexes bearing groups with a range of electron-withdrawing abilities has been synthesized. After submitting these complexes to the intermolecular Pauson-Khand reaction with norbornadiene, electron-deficient substrates afforded up to 26% of the unexpected endo-cyclopentenone.     

Synthesis and structural, spectroscopic and magnetic studies of two new polymorphs of Mn(SeO3)·H2O

Two new manganese(II) selenite polymorphs with formula Mn(SeO₃)·H₂O have been synthesized by slow evaporation from an aqueous solution. The crystal structure of both compounds (1) and (2) have been solved from X-ray diffraction data. The structure of (1) was determined from single-crystal X-ray diffraction techniques. The compound crystallizes in the Ama2 space group, with a=5.817(1), b=13.449(3), and Z=4. The structure of (2) has been solved from X-ray powder diffraction data. This phase crystallizes in the P2₁/n space group with unit-cell parameters of a=4.921(3), b=13.121(7), , β=90.03(2)° and Z=4. Both polymorphs exhibit a layered structure formed by isolated sheets of MnO₆ octahedra and (SeO₃)²⁻ trigonal pyramids in the (010) plane. These layers, which contain one manganese and selenium atom crystallographically independent, are formed by octahedra linked between them through the selenite oxoanions. The difference of both compounds consists in the stacking of the layers along the b-axis. The IR spectra show the characteristic bands of the selenite anion. Studies of luminescence performed at 6 K and diffuse reflectance spectroscopy have been carried out for both phases. The Dq and Racah (B and C) parameters, from luminescence and diffuse reflectance spectroscopy, are Dq=705, B=750, for (1) and Dq=720, B=745, for (2). The ESR spectra of both compounds are isotropic with g-values of 1.99(1). Magnetic measurements indicate the presence of antiferromagnetic couplings in both phases. The J-exchange parameters have been estimated by fitting the experimental magnetic data to a model for square-planar lattice. The values obtained are J/k=-0.83, −0.91 K and J^′/k=-0.97, −1.20 K, for polymorphs (1) and (2), respectively.     

La solution solide Cr1−xIrxO2

A new solid solution Cr_1?xIr_xO₂ (0 ≤ x ≤ 1) has been prepared using oxidizing agents under pressure. The magnetic study shows the importance of the spin-orbit coupling and the weakening of the ferromagnetic interactions with increasing iridium content.     

Reactions of pyrrolidine enamines of cyclic and acyclic 3,4-dioxobutanoic acid Derivatives with dimethyl acetylenedicarboxylate. A new case of atropoisomerism.

Reaction conditions and structure of the starting enamines (cyclic or open-chain) determine greatly the final products of the title reactions. Whereas in benzene and acetonitrile, DMAD and 1 give a mixture of the diastereoisomeric dienamines 5, in methanol they afford pirrolizine 3. Enaminofuranones 2 and 10 furnish the corresponding “Michael adducts” 7a,b,c and 11a,b,c but fail to yield pirrolizines. It has been demonstrated that above b and c adducts differ exclusively on the arrangement of groups around a chiral axis.     

Additions of enantiopure alpha-sulfinyl carbanions to (S)-N-sulfinimines: asymmetric synthesis of beta-amino sulfoxides and beta-alphamino alcohols

The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported.     

Assessment of Four Inter-Comparison Exercises in Organic Elemental Analysis

 Four inter-comparison exercises on organic elemental analysis were carried out between 1997 and 2001 by the Department of Analytical Chemistry of the University of Barcelona, together with the Microanalysis Service and the Institute of the Marine Sciences, which both belong to the CSIC in Barcelona, and the University of A Coru?a. More than sixty laboratories participated in these exercises. Here we describe the design and characteristics of the trials, the samples and the homogeneity tests applied. We report the results obtained for the analysis of carbon, hydrogen, nitrogen, sulphur and oxygen, their statistical analysis, and the most relevant aspects of the technical discussion meetings. Received December 20, 2001; accepted March 18, 2002; published online July 22, 2002     

Convergent stereocontrolled synthesis of substituted exo-glycals by Stille cross-coupling of halo-exo-glycals and stannanes

(Z)-exo-Glycals can be conveniently prepared in a convergent manner by Stille cross-coupling of (Z)-halo(Br,I)-exo-glycals and aryl or alkenyl stannanes, the latter are readily obtained by addition of tributylstannyl radicals to terminal alkynes.     

New oxamidato-bridged Cu(II)-Ni(II) complexes: supramolecular structures with thiocyanate ligands and hydrogen bonds. Magnetostructural studies: DFT calculations

Four new supramolecular compounds of Cu(II)-Ni(II) have been synthesized and characterized: [Cu(Me(2)oxpn)Ni(mu-NCS)(H(2)O)(tmen)](2)(ClO(4))(2) (1), [Cu(Me(2)oxpn)Ni(mu-NCS)(H(2)O)(tmen)](2)(PF(6))(2) (2), [Cu(oxpn)Ni(mu-NCS)(NCS) (tmen)](n) (3), and [Cu(Me(2)oxpn)Ni(mu-NCS)(NCS)(tmen)](n) (4), where oxpn = N,N'-bis(3-aminopropyl)oxamidate, Me(2)oxpn = N,N'-bis(3-amino-2,2'-dimethylpropyl)oxamidate, and tmen = N,N,N',N'-tetramethylethylenediamine. Their crystal structures were solved. Complexes 1 and 2 have the same tetranuclear cationic part but a different counteranion. The cationic part consists of two [Cu(Me(2)oxpn)Ni] moieties linked by SCN(-) bridged ligands and intra-tetranuclear hydrogen bonds. In the case of complex 3, a two-dimensional system was built, the thiocyanate ligand linking the dinuclear units gives a chain, and the chains are linked together by hydrogen bonds; intrachain hydrogen bonds are also present. For complex 4, the thiocyanate ligands produce intermolecular linkages between the dinuclear entities, giving a one-dimensional system; intrachain hydrogen bonds are also present. The magnetic properties of the four complexes were studied by susceptibility measurements vs temperature. DFT calculations were made to study the contribution of the SCN(-) and hydrogen bond bridges in the magnetic coupling.     

Magnetic properties of cyano-bridged Ln3+-M3+ complexes. Part I: trinuclear complexes (Ln3+ = La, Ce, Pr, Nd, Sm; M3+ = FeLS, Co) with bpy as blocking ligand

The reaction of Ln(NO3)3(aq) with K3[Fe(CN)6] or K3[Co(CN)6] and 2,2'-bipyridine in water/ethanol led to eight trinuclear complexes: trans-[M(CN)4(mu-CN)2{Ln(H2O)4(bpy)2}2][M(CN)6].8H2O (M = Fe3+ or Co3+, Ln = La3+, Ce3+, Pr3+, Nd3+, and Sm3+). The structures for the eight complexes [La2Fe] (1), [Ce2Fe] (2), [Pr2Fe] (3), [Nd2Fe] (4), [Ce2Co] (5), [Pr2Co] (6), [Nd2Co] (7), and [Sm2Co] (8) have been solved; they crystallize in the triclinic space group P and are isomorphous. They exhibit a supramolecular 3D architecture through hydrogen bonding and pi-pi stacking interactions. A stereochemical study of the nine-vertex polyhedra of the lanthanide ions, based on continuous shape measures, is presented. No significant magnetic interaction was found between the lanthanide(III) and the iron(III) ions.