Study in Aqueous Solutions of Bioactive 2-Pyridineformamide-Derived Thiosemicarbazones and Their Iron(II) and Iron(III) Complexes

The binary systems of iron(II) and iron(III) with 2-pyridineformamide thiosemicarbazone (H2Am4DH) and its N(4)-methyl (H2Am4Me), N(4)-ethyl (H2Am4Et) and N(4)-phenyl (H2Am4Ph) derivatives were studied in aqueous solution by pH-potentiometry, ultraviolet–visible spectroscopy and EPR spectra. The formation constants of the iron(II) and iron(III) complexes were calculated from potentiometric and electronic absorption data at 25 °C and ionic strength μ = 0.1 mol·L^?1 using the HYPERQUAD program. The values of the formation constant of the FeL species decrease in the order Fe:H2Am4DH > Fe:H2Am4Me ≈ Fe:H2Am4Et > Fe:H2Am4Ph in the same way as the basicity of the ligands. The species distribution diagrams show that the species FeL₂ predominates at physiological pH in the Fe:H2Am4DH, Fe:H2Am4Me and Fe:H2Am4Et systems. The similar EPR spectra of these iron(III) binary systems indicate the same coordination spheres around the metallic center and the EPR g values suggests that the unpaired electron is in the d_xy orbital, indicating a d _xz ² d _yz ² d _xy ¹ ground state configuration for the complexes. For the Fe(III):H2Am4Ph system the EPR results indicated dimerization and antiferromagnetic interaction due to the presence of only one thiosemicarbazone ligand around the metallic center.     

(3R,11aR)-3-Phenyl-2,3,11,11a-tetrahydro-[1,3]oxazolo[3,2-b]-[2]benzazepin-5(10H)-one as a chiral building block for the asymmetric synthesis of 3-substituted 2-benzazepines

A five-step synthesis of the chiral building block cis-2 is described. Key steps in the synthesis were a Heck reaction of 1-bromo-2-iodobenzene with allyl alcohol, the introduction of a carboxy group after Br/Li-exchange, and the diastereoselective formation of the tricyclic oxazolidine system cis-2. Activation of cis-2 with TiCl₄ led to formation of a carbenium ion, which was attacked by allyltrimethylsilane exclusively from the Re-face leading to the (3S)-configured 2-benzazepinone 8 in 65% yield. The configuration of the new stereogenic center was determined by X-ray crystal structure analysis, which is the basis for the proposed mechanism of this transformation. Enantiomerically pure 3-substituted 2-benzazepines represent interesting drug candidates.     

Unexpected formation of anti-1,2-W2(SBut)2(NMe2)4 in the thiolysis of gauche-1,2-W2Cp2(NMe2)4 and W2COT(NMe2)4 with ButSH

Thiolysis of W₂Cp₂(NMe₂)₄ and W₂COT(NMe₂)₄ with excess Bu^tSH leads to cleavage of the respective carbocyclic rings from the ditungsten center and formation of the compound anti-1,2-W₂(SBu^t)₂(NMe₂)₄ which was characterized via a single-crystal X-ray diffraction study. This product was found to be isostructural with its dimolybdenum analogue. The compound is a prototypical ethane-like dimer having a WW bond distance of 2.3011(3) Å and thiolate ligands in an anti configuration about the WW bond. The thiolysis reactions for both dimethylamide precursors are contrasted with the results of their respective alcoholysis reactions.     

Synthesis of C3-substituted enantiopure 2-(p-tolylsulfinyl)-furans: the sulfoxide group as a chiral inductor for furan dienes as precursors of a wide variety of chiral intermediates

(−)-(1R,2S,5R)-Menthyl (S_S)-p-toluenesulfinate and its enantiomer are a common source for a chiral sulfoxide group in organic synthesis, by means of nucleophilic substitution. The replacement of the menthyloxy group, with complete inversion of configuration at the sulfur center of the chiral sulfoxide, allows the inclusion of this organic function into numerous substrates, with defined stereochemistry and high enantiomeric purity. Nine C3-substituted, enantiomerically pure, 2-sulfinylfurans were prepared by this synthetic methodology with moderate to high yields. These enantiopure C3-substituted 2-sulfinylfurans can be used as chiral dienes for [4+3] cycloaddition reactions and in other chemical transformations, in which π-facial selectivity should be induced in order to obtain enantioselective reactions.     

Preparation,properties and structure of stable ionic dialkylbis(2,2′-bipyridine)cobalt(III) tetraalkylaluminate and related complexes

Two types of dialkylcobalt(III) complexes containing the 2,2′-bipyridine ligand have been isolated as products of the reactions of tris(2,4-pentanedionato)cobalt(III) (Co(acac)₃), 2,2′-bipyridine (bpy), and alkylaluminums in diethyl ether. When high Al/Co ratios (Al/Co > 7) were used, ionic complexes, dialkylbis(2,2′-bipyridine)cobalt(III) tetraalkylaluminates, [CoR₂(bpy)₂][AlR₄] (R = CH₃, C₂H₅) were obtained exclusively. Similar reactions at lower ratios (Al/Co - 1.5–2.0) gave neutral CoR₂(acac)(bpy) (R = CH₃, C₂H₅, n-C₃H₇, i-C₃H₇). These compounds were characterized by IR and NMR spectroscopy as well as by elemental analysis and chemical reactions. Molecular structural analysis of the cationic dimethylcobalt compound confirmed the cis configuration. Stepwise formation of [CoR₂(bpy)₂][AlR₄] from Co(acac)₃ is postulated and the mechanism of the alkylation reaction is discussed.     

A novel highly stereoselective synthesis of chiral 5- and 4,5-substituted 2-oxazolidinones

A novel highly stereoselective synthesis of chiral mono- and bicyclic 4- and 4,5-substituted 2-oxazolidinones starting from β-keto esters was developed. After bioreduction with S. cerevisiae the resulting homochiral β-hydroxy esters are transformed into their hydrazides. Treatment with NaNO₂/H⁺ then furnishes 2-oxazolidinones in high e.e. (∼99%) and d.e. (>99%). The ring formation proceeds via a highly concerted sextet rearrangement with full retention of configuration at the stereocentres. Enantiopure 1,2-amino alcohols can subsequently be obtained by saponification of the 2-oxazolidinone products.     

Synthesis of both enantiomers of cyclic methionine analogue: (R)- and (S)-3-aminotetrahydrothiophene-3-carboxylic acids

A method of synthesizing an optically active cyclic methionine analogue, 3-aminotetrahydrothiophene-3-carboxylic acid (At₅c), is described. A Bucherer–Bergs reaction of 4,5-dihydro-3(2H)-thiophenone and the subsequent alkaline hydrolysis of a hydantoin, followed by Cbz protection of the amine, afforded racemic Cbz-At₅c (±)-3 in excellent yield. Diastereomeric esters derived from Cbz-At₅c (±)-3 and (R)-BINOL could be separated by column chromatography to give both diastereomers with >99% de. X-ray crystallographic analysis revealed the absolute configuration of the synthesized amino acid derived from the less polar diastereomeric ester to be (S).     

Optically active (2-aminomethylferrocenyl) phosphines with the phosphorus chiral center

The reaction of an enantiomeric planar-chiral palladium derivative of dimethyl-aminomethylferrocene with PhMePLi in THF at room temperature afforded a 1.5∶1.0 mixture of diastereomeric aminophosphines containing the phosphorus asymmetrical center along with a chiral plane. The absolute configuration of the phosphorus atom was determined based on the X-ray diffraction data for the complex of the minor diastereomer with PdI₂. The presence of the (S)-chiral plane in the initial palladium compound favors the predominant formation of the product with the (S)-configuration of the phosphorus center.     

Preparation of enantiomerically pure (3E)-alkyl-4-(hetero-2-yl)-2-hydroxybut-3-enoates by Candida parapsilosis ATCC 7330 mediated deracemisation and determination of the absolute configuration of (3E)-ethyl-4-(thiophene-2-yl)-2-hydroxybut-3-enoate

Deracemisation of racemic (3E)-alkyl-4-(hetero-2-yl)-2-hydroxybut-3-enoates using Candida parapsilosis ATCC 7330 resulted in the formation of one enantiomer in high enantiomeric excess [up to >99% ee] and isolated yields [up to 79%]. The absolute configuration of the enantiomerically pure (3E)-ethyl-4-(thiophene-2-yl)-2-hydroxybut-3-enoate as determined by ¹H NMR of the Mosher esters was found to be (S).     

Trading N and O: asymmetric syntheses of β-hydroxy-α-amino acids via α-hydroxy-β-amino esters

Both diastereoisomers of 2-amino-3-hydroxybutanoic acid and 2-amino-3-hydroxy-3-phenylpropanoic acid have been prepared from enantiopure α-hydroxy-β-amino esters via the intermediacy of the corresponding cis- and trans-aziridines. Aminohydroxylation of two α,β-unsaturated esters produced enantiopure 2,3-anti-α-hydroxy-β-amino esters in >99:1 dr. Subsequent epimerisation at the C(2)-position via a sequential oxidation/diastereoselective reduction protocol gave the corresponding enantiopure 2,3-syn-α-hydroxy-β-amino esters in >99:1 dr. These syn- and anti-substrates were then converted into the corresponding N-Boc protected cis- and trans-aziridines, respectively, via a three step reaction sequence: (i) hydrogenolysis and in situ N-Boc protection; (ii) OH-activation; and (iii) aziridine formation. Subsequent regioselective ring-opening of the C(3)-methyl-aziridines with Cl₃CCO₂H proceeded with inversion of configuration to give the corresponding 2-amino-3-trichloroacetate esters, whereas the analogous reaction with the C(3)-phenyl-aziridines resulted in rearrangement to the corresponding oxazolidin-2-ones with retention of configuration. In each case, hydrolysis of the products from these ring-opening reactions produced the corresponding enantiopure β-hydroxy-α-amino acids as single diastereoisomers.     

Syntheses et isomerisation de complexes de la serie des derives halocarbonyle due fer: [FeX(CO)5−nLn]+, FeX2(CO)4−nLn et [FeX3(CO)3]- (L = PMe3; n = 1, 2, 3; X = Cl,Br, I)

The synthesis of a number of neutral, cationic and anionic halocarbonyl complexes of iron having the formula [FeX_m(CO)_6?m?nL_n]^2?m is described. The determination of their molecular configuration by infrared, NMR and dipole moment measurements allowed the study of several of their photochemical isomerization reactions, the mechanism of these reactions is explained in some cases by the intermediary formation of cationic complexes.     

m-nitrobenzyl alcohol electrochemistry in fast atom bombardment mass spectrometry

The efficacy of m-nitrobenzyl alcohol (NBA) as a solvent (matrix) for fast atom bombardment (FAB) mass spectrometry of a group of pyrazolate-bridged dirhodium A-frame complexes has been assessed. Although NBA is frequently used to mitigate the formation of artifacts in FAB/MS of organometallics and other materials susceptible to bombardment-induced reactions, substantial evidence indicates that such reactions cause the formation of artifacts in the spectra obtained here. Parallel absorption spectroscopic studies have established that NBA is capable of inducing both oxidation and reduction reactions independent of ion bombardment, depending on analyte reduction half-wave potential (E_1/2). From the known electrochemistry of the complexes studied, it can be estimated that 1020 mV > E_1/2 > 500 mV for the reaction of NBA serving as a reducing agent, while 500 mV > E_1/2 > 424 mV for the reduction potential of NBA. However, in the presence of bombardment the former E_1/2 must be at least as low as 356 mY, and the latter E_1/2 must be at least as high as 1188 mY. The kinetics of redox reactions involving NBA, and therefore their influence on the appearance of FAB mass spectra, will be highly sample-dependent. However, this study illustrates an important potential role for redox reactions when NBA is used as a solvent, especially in the presence of bombardment in FAB/MS. Although analyte reaction products could be identified, substantial efforts aimed at identifying NBA oxidation and reduction products did not yield any definitive results due to the complexity of product mixtures.     

Evaluation of HX (X = Cl,Br, O) product distributions from chemiluminescence. I. H atom reactions

The HX product state distributions from the H+Cl₂, Br₂, NO₂Cl, PCl₃, and NO₂ reactions have been studied by the infrared chemiluminescence technique in two different laboratories with two types of reactors; a fast-flow system with = 1 Torr of Ar buffer gas and a low-pressure, cold-wall system (usually called the cold-wall arrested-relaxation method). The same Einstein coefficients were used in both laboratories to convert intensities to populations and emphasis is placed upon evaluation of the reliability of the resulting vibrational-rotational HX distributions. Good agreement was found between the HX distributions from the cold-wall reactors from the two laboratories and for both types of reactors for all of the reactions, except PCl₃. For the H+Cl₂, Br₂ and NO₂ reactions, our general results are in good accord with presently accepted data; but, our experiments provide somewhat more detail than in the literature. The NO₂Cl results are new and <f_v(HCl) > = 0.40 and <f_R(HCl) > = 0.01. The H+PCl₃ reaction appears to proceed by two channels and the HCl chemiluminescence cannot be assigned only to HCl formation via direct Cl atom abstraction.     

Complex formation equilibria between Ag(I) and thioureas in n-propanol

Complex formation equilibria between Ag(I) and thiourea or N-alkyl-substituted thioureas have been investigated in n-propanol by potentiometry at 10 °C intervals from 5 to 50 °C. Stepwise formation of tris-coordinated AgL_n (n = 1-3) complexes has been found for the majority of the ligands. ΔH and ΔS values for the complex formation reactions have been evaluated from the dependence of ln β_n on temperature. The alkyl-substituents affect the ligand affinities in different ways in relation with the coordination level n.The reactions are exothermic with few exceptions. Enthalpy favoured complex formation with negative dependence of ΔG on temperature (ΔS > 0) have been found.The enthalpy and entropy changes for the stepwise complex formation equilibria are correlated by two linear compensative relationships with the same isoequilibrium temperature 50-51 °C.     

Stereoselective synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-ol and its propionate,the sex pheromones of pine sawflies

The stereoselective synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-ol (diprionol) and its propionate, the sex pheromones of pine sawflies (Neodiprion sp. and other), in high enantiomeric purity was achieved from (1R,3S)-2,2-dichloro-3-methylcyclopropanecarboxylic acid. The carbon skeleton of diprionol was formed via copper-catalyzed cross-coupling reactions and diastereoselective methylation of the intermediate chiral α-methylbranched aldehyde with MeTi(Oi-Pr)₃ in the presence of [(R,R)-TADDOL]Ti(Oi-Pr)₂. The latter transformation leads to a syn-adduct with high stereoselectivity, which depends on the presence and configuration of the α-stereogenic center in the aldehyde. The diastereomeric purity of (2S,3S,7S)-diprionol can be substantially increased via crystallization of its 3,5-dinitrobenzoate.     

Phenoxyaluminium compounds: VI. Complex and reaction mechanism of methylaluminium compounds with anisole

The reactions of anisole with organoaluminium compounds Me_nAlX_3−n have been investigated.The formation of a complex is the first reaction step, followed by cleavage and elimination of the gases MeX and small amounts of hydrocarbons. The yield of the gases and the cleavage rate decreases in the order: AlCl₃ >/ MeAlCl₂ > Me₂AlCl > Me₃Al and Me₂AlI > Me₂AlCl > Me₂AlBr. For most of the investigated reactions a marked decrease in gas evolution was observed after a short period of time. This is explained by the formation of an almost inactive mixed dimer (I) which at the

reaction temperature is more stable than the Me₂(Cl)Al : O(Me)Ph complex. It is suggested that dimer I is formed after the intramolecular reaction of the 2 : 1 complex II after elimination of MeX.

     

Design of C2-symmetric salen ligands and their Co(II)- or Yb(III)-complexes,and their role in the reversal of enantioselectivity in the asymmetric Henry reaction

Reversal of enantioselectivity in asymmetric Henry reactions was achieved with novel chiral C₂-symmetric salen ligands bearing morpholine moieties by changing the Lewis acid center from Co(II) to Yb(III). The possible transition state models were supported by mass spectrometry experiments.     

Features of catalyzed hydration of 2-(dichloromethyl)-<Emphasis Type="Italic">N</Emphasis>-[(1<Emphasis Type="Italic">R</Emphasis>)-1-phenylethyl)]cyclopent-3-ene-1-carboxamides

The hydration of gem-dichloromethyl group in 2-(dichloromethyl)-N-[(1R)-1-phenylethyl)]cyclopent-3-ene-1-carboxamides in aqueous acetonitrile catalyzed by AgNO₃, FeCl₃·6H₂O, PdCl₂, and BaO was investigated. The optimum results were obtained at the use of BaO. It was demonstrated, that Pd-catalyzed reactions initiated intermolecular ether formation from the primary hydration products, bicyclic amides.     

The energy and geometric characteristics of the transition state in reactions of RO<Stack><Subscript>2</Subscript><Superscript>•</Superscript></Stack> with carbonyl compound C-H bonds

The energy and geometry of the transition state in reactions of the ethyl peroxyl radical with ethane, ethanol (its α and β C-H bonds), acetone, butanone-2, and acetaldehyde were calculated by the density functional theory method. In all these reactions (except EtO_2/? + ethanol α C-H bond), the C…H…O reaction center has an almost linear configuration (φ = 176° ± 2°); polar interaction only influences the r ^≠ (C…O) interatomic bond. In the reaction of EtO_2/? with the ethanol α C-H bond, it is the O-H…O H-bond formed in the transition state that determines the configuration of the reaction center with the angle φ(C…H…O) = 160°. The results were used to estimate the r ^≠ (C…H) and r ^≠ (O…H) interatomic bonds in the transition state by the method of intersecting parabolas and the contribution of polar interaction to the activation energy of reactions between peroxyl radicals and aldehydes and ketones.     

Asymmetric cycloaddition reactions between 2-benzopyrylium-4-olates and 3-(2-alkenoyl)-2-oxazolidinones in the presence of 2,6-bis(oxazolinyl)pyridine-lanthanoid complexes

Highly enantioselective (96% ee) and endo-selective (>99:1) cycloaddition reactions were observed between carbonyl ylides, generated from o-(p-bromobenzyloxy)carbonyl-α-diazoacetophenone, and 3-crotonoyl-2-oxazolidinone using (4S,5S)-Pybox-4,5-Ph₂-Yb(OTf)₃ (20 mol %) as the chiral Lewis acid catalyst. In contrast, high exo-selectivity (exo/endo=82:18; 96% ee, exo) was observed for the reaction of o-methoxycarbonyl-α-diazoacetophenone with 3-acryloyl-2-oxazolidinone under similar conditions as reported previously. In the case of cycloaddition reactions between 2-benzopyrylium-4-olate, generated from o-methoxycarbonyl-α-diazoacetophenone, and 3-cinnamoyl- or 3-[(E)-3-(ethoxycarbonyl)propenoyl]-2-oxazolidinones, using the same chiral Lewis acid, the reaction favored the endo-adduct with relatively good enantioselectivity (72 and 78% ee, respectively).