M. D. Estrada

A novel highly diastereoselective synthesis of chiral dihydrothiophenes from mesoionic compounds

Thioisomunchnones undergo 1,3-dipolar cycloaddition with chiral nitroalkenes to afford stereoselectively 4,5-dihydrothiophenes by means of an unprecedented fragmentation of cycloadducts; the structures of these products have been established by single crystal X-ray structure analyses.

A new synthesis of 6-oxopyrimidinium-4-olates. Theoretical study of the regioselective cycloaddition of arylisocyanates with a 1,3-thiazolium-4-olate system

Abstract A new and regioselective synthesis of 6-oxopyrimidinium-4-olate systems ( 13–21 ) is described, involving the 1,3-dipolar cycloaddition of the 1,3-thiazolium-4-olate 12 with arylisocyanates. MNDO and AM1 calculations rationalise the reactivity and regioselectivity experimentally observed.

Silica gel-catalysed addition of methyl nitroacetate to 1,2: 3,4-di-O-isopropylidene-α-d-galacto-hexodialdo-1,5-pyranose and 2,3-O-isopropylidene-d-glyceraldehyde. Crystal structure of methyl 7-acetamido-7-deoxy-1,2 : 3,4-di-O-isopropylidene-l-threo-α-d-galacto-octopyranuronate

Abstract The addition of methyl nitroacetate to 1,2:3,4- di -O- isopropylidene-α- d -galacto- hexodialdo-1,5-pyranose (5) and to 2,3-O- isopropylidene- d -glyceraldehyde (6) in the presence of silica gel led stereoselectively to the formation of only (from 5) or mainly (from 6) two of the four possible nitroaldols in high yield. The catalytic action of silica gel was required in the reaction of 6, but not in that of 5. Isolation of a crystalline, reduced and N -acetylated derivative from the mixture of nitroaldols (7 + 8) obtained from 5 allowed for the determination of its crystal structure, showing that it has the 6 R , 7 R absolute configuration (one of the two possible 6,7- threo configurations) by X-ray diffraction methods. Therefore, the same 6 R configuration was also assigned to the nitroaldols 7 and 8, which on the basis of the easy α-epimerisation of the α-nitro esters should differ only in the configuration at C-7. A pair of amino alcohols obtained from the same mixture of nitroaldols were separately transformed into a 4,5- cis - and a 4,5- trans -oxazoline, the configurations of which were correlated with the C-6,7 relative configuration of the respective amino alcohols and also the respective nitroaldol. The Felkin model explained the high stereoselectivity observed. The configurations of the two predominant nitroaldols obtained from 6 were tentatively assigned by applying the Felkin model.

Sulfoaminoglucitols: synthesis of 2-amino-2,3 (and 2,6)-dideoxy-d-glucitol-3 (and 6)-sulfonic acids and X-ray crystal structure of the monohydrate of the 6-sulfo derivative

Abstract 2-Amino-2,3-dideoxy- d -glucitol-3-sulfonic acid (3) and 2-amino-2,6-dideoxy- d -glucitol-6-sulfonic acid (4) were prepared by reduction of 2-amino-2,3 (and 2,6)-dideoxy- d -glucopyranose-3 (and 6)-sulfonic acids with sodium borohydride. The crystal structure of 4 monohydrate (C 6 H 15 NO 7 S · H 2 O) is orthorhombic, space group P 2 1 2 1 2 1 with unit cell dimensions a = 8.289(2), b = 24.548(5), and c = 5.149(2) A . A planar zig-zag conformation is observed in which N-2 and O-4 atoms are aligned 1,3-parallel, stabilized by an intramolecular hydrogen bond (N-H … O–4). The sulfo and the amino group form a zwitterion and two conformations are found for the ammonium group.

Synthesis of methyl 3,6-dideoxy-3-C-methoxycarbonyl-3-C-nitrohexopyranosides: crystal structure of methyl 3,6-dideoxy-3-C-methoxycarbonyl-3-C-nitro-α- l-galacto-hexopyranoside☆

Abstract Methyl 3,6-dideoxy-3- C -methoxycarbonyl-3- C -nitro-α- l - galacto -hexopyranoside ( 3 ) has been synthesised by periodate oxidation of methyl α- l -rhamnopyranoside followed by condensation with methyl nitroacetate, and its structure has been established on the basis of its analytical and spectral data, and by an X-ray diffraction study. Crystals of 3 are orthorhombic, space group P 2 1 2 1 2 1 , with a = 10.009(3), b = 15.3610(3), c = 7.986(3) A, and Z = 4. Molecular-packing analysis in the atom—atom approach yields an equilibrium configuration in good agreement with the experimental findings.

Spectroscopic and X-ray crystallographic studies of the potassium salt of hexameric malondialdehyde

Abstract The crystalline potassium salt of a hexameric form of malondialdehyde has been obtained and shown to be racemic potassium hydrogen bis [trans-4-(1,3-dioxopropan-2-yl)-5-formyl-2-hydroxy-3,4-dihydro-2H-pyran].

Diethyl 6(R)-3-(4-chlorophenyl-6-(tetra-O-acetyl-D-arabino-threitol-1-yl)-1,2,3,6-tetrahydro-1,2,3,4-tetrazine-1,2-dicarboxylate, C26H33ClN4O12

The configurations around the chiral centres C53, C52, C51 and C5 are R, S, R and R, respectively, corresponding to a D-arabino conformation. The tetrahydrotetrazine ring has a conformation close to that of a half-boat. Packing of the molecules is governed by normal van der Waals contacts

X-ray structure and hydrogen-bonding study of taurine and N-(glucitol-1-yl)taurine

Sucrose is one of the most abundant pure organic chemicals in the world and the one most widely known to nonchemists. In recent years, sucrose is reported as a functional material for developing alternative biofuel cells which use biocatalysts to convert energy from sugar into electrical power. However, melting points among sucrose crystals with high purity are occasionally different with each other and the melting points quoted references range from 160°C to 192°C . Although many researchers have studied on the melting point by using differential scanning calorimetry (DSC) or optical microscope, there are few reports on the microscopic observation of the crystalline noncrystalline phase transition of sucrose. In the present work, using high-temperature X-ray diffraction (HTXRD) and simultaneous instruments for X-ray diffractometry and differential scanning calorimetry (XRD-DSC), we have investigated some possible factors involved in the noncrystallization from the crystalline state under isothermal and non-isothermal conditions. The sucrose from commercial source and its recrystallized one were used. XRD-DSC results showed the occurrence of two peaks around 150 °C and 175°C for recrystallized sucrose at heating rate of 10°C/min, while no significant change in the XRD patterns at the first peak was observed during the heating process. The noncrystallization point moved to high temperature as the rate of heating was increased. The Rietveld analysis of HTXRD data is a key point for understanding the mechanism and kinetics of crystalline-noncrystalline phase transition of sucrose under isothermal condition.

N-Phenyl-2-phenyliminotetrahydro-1,3-thiazole-2-carbothioamide, C16H15N3S2

The thiazolidine ring in the title compound has an envelope conformation, E 4 , with a C atom out of the plane of the ring. The C-S and C-N bond lengths clearly show the typical resonance of the thiourea group. The molecules are linked by van der Waals forces and an intramolecular N...N hydrogen bond is present

Structure and Molecular-Packing Analysis of a Heptofuranosoimidazolidine-2-Thione

1-(4-Bromophenyl)-3-ethyl-(3,5,6,7-tetra-Oacetyl1,2-dideoxy-D-glycero-fl-D-talo-heptofuranoso)* IUPAC name: 1-{6-acetoxy-3-bromophenyl-2-thioxo-2,3,3a,5,6,6a-tetrahydro1H-furo[2,3-d]imidazol-5-yl }propane1,2,3-triyl triacetate. [2,1-d]imidazolidine-2-thione, C24H29BrN209S , M r-601.46, orthorhombic, P212~21, a = 15-634 (3), b 22.749 (6), c = 7.714 (2) A, V = 2743 (1) A 3, Z = 4, D x = 1.46 Mg m -3, 2(Mo Ka) = 0.7107 A , /t = 1.60 mm -~, F ( 0 0 0 ) 1240, room temperature, final wR --0.052 for 1643 observed reflexions. 0108-2701/87/061134-05501.50