Enantioselective reduction of C=O and C=N bonds by TADDOL-containing aluminum hydride reagents based on NaAlH4 and AlH3

Prochiral substrates (alkyl aryl ketones, cyclopropyl methyl ketone, 1-indanone, 1-tetralone, ethyl 2-oxo-4-phenylbutyrate, and N-(diphenylphosphinyl)acetophenoneimine) were subjected to asymmetric reduction with aluminum hydride reagents, which were prepared by modifications of NaAlH₄ or AlH₃ with chiral ,,","-tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOL). The effects of the nature of the substituents in TADDOL, the structure of the prochiral substrate, and the reaction conditions on the stereochemistry of reduction were investigated. The highest enantioselectivity (70—90% ee) was achieved upon reduction of alkyl aryl ketones and N-(diphenylphosphinyl)acetophenoneimine with NaAl(TADDOLate)H₂ in THF or diglyme at a temperature from –70 to –20 °C. The mechanism of asymmetric induction in the reduction reactions of ketones with aluminum hydride reagents is discussed. The stereochemical results of reduction were explained by comparing three-dimensional models of the most probable transition states.     

Stereo-controlled anti-hydromagnesiation of aryl alkynes by magnesium hydrides

A concise protocol for anti-hydromagnesiation of aryl alkynes was established using 1 : 1 molar combination of sodium hydride (NaH) and magnesium iodide (MgI₂) without the aid of any transition metal catalysts. The resulting alkenylmagnesium intermediates could be trapped with a series of electrophiles, thus providing facile accesses to stereochemically well-defined functionalized alkenes. Mechanistic studies by experimental and theoretical approaches imply that polar hydride addition from magnesium hydride (MgH₂) is responsible for the process.

Anti-hydromagnesiation of aryl alkynes was facilitated solely by magnesium hydride. The resulting alkenylmagnesium intermediates were functionalized with various electrophiles to afford stereochemically defined tri-substituted alkenes.     

Catalytic Reduction of Alkyl and Aryl Bromides Using Propan‐2‐ol

Milstein's complex, (PNN)RuHCl(CO), catalyzes the efficient reduction of aryl and alkyl halides under relatively mild conditions by using propan‐2‐ol and a base. Sterically hindered tertiary and neopentyl substrates are reduced efficiently, as well as more functionalized aryl and alkyl bromides. The reduction process is proposed to occur by radical abstraction/hydrodehalogenation steps at ruthenium. Our research represents a safer and more sustainable alternative to typical silane, lithium aluminium hydride, and tin‐based conditions for these reductions.     

The cleavage of meso-epoxides with homochiral thiols: synthesis of (+)- and (−)-trans-1-mercaptocyclohexan-2-ol

The synthesis of (+)- and (−)-trans-1-mercaptocyclohexan-2-ol is described. Ring opening of cyclohexene oxide with (−)-4-methoxybenzylnopan-3(R)-thiol 1a followed by oxidation gives two readily separable diastereomeric sulfoxides. These sulfoxides display very different thermal stability but both undergo regio-specific syn-elimination to give cyclohexan-1-ol-2-sulfenic acid that can be reacted in situ with 3,5-dimethylthiophenol to give a mixed disulfide. Reduction of these disulfides with lithium aluminium hydride gives the title compounds in enantiomerically pure form.     

氢化铝锂一步还原β-烯胺酮合成1,3-胺基醇

β-烯胺酮类化合物是重要的有机合成砌块, 通过还原可用来合成具有广泛用途的1,3-胺基醇类化合物. 文献报道氢化铝锂还原β-烯胺酮为1,3-胺基醇, 只能采用两步还原的方法. 在四氢呋喃中采用过量的氢化铝锂于回流下将3-二甲胺基-1-芳基-2-丙烯酮高产率地一步还原为N,N-二甲基-3-羟基-3-芳基丙胺, 为该类化合物的合成提供了一个新方法.     

Simple and efficient copper-catalyzed S-arylation of diaryl disulfides with triarylbismuthanes under aerobic conditions

Novel and simple copper-catalyzed C(aryl)-S bond formation of diaryl disulfides with bismuth reagents is described. Reactions of diaryl disulfides with triarylbismuthanes in the presence of CuOAc (10 mol %) and 1,10-phenanthroline (10 mol %) under aerobic conditions led to the formation of unsymmetrical diaryl sulfides in satisfactory yields. The reaction is atom-economic and all three aryl groups of the triarylbismuthanes and both sulfanyl groups of the diaryl disulfides could be transferred to the coupling products.     

Azabrendanes. III. Synthesis of stereoisomeric exo‐ and endo‐5‐acylaminomethyl‐exo‐2,3‐epoxybicyclo[2.2.1]heptanes and their reduction by lithium aluminum hydride

A number of stereoisomeric N‐[aryl(alkyl, cycloalkyl)carbonyl]‐exo(endo)‐5‐aminomethylbicyclo[2.2.1]hept‐2‐enes have been synthesized from bicyclo[2.2.1]hept‐2‐en‐exo(endo)‐5‐carbonitrile via reduction of the latter by lithium aluminum hydride and subsequent reactions of the resulting amines with aryl(alkyl, cycloalkyl)carbonyl chlorides and anhydrides. The direction of reaction of amides with peroxy acids does not depend on orientation of substituents in the bicyclic fragment: that is, for both exo‐ and endo‐isomers the epoxidations are completed by the formation of N‐[aryl(alkyl, cycloalkyl)carbonyl]‐exo(endo)‐5‐aminomethyl‐exo‐2,3‐epoxybicyclo[2.2.1] heptanes. The reduction of stereoisomeric epoxides by lithium aluminium hydride proceeds in different directions; that is, isomers with an exo‐oriented amido group form the substituted exo‐5‐alkylaminomethyl‐exo‐2,3‐epoxybicyclo[2.2.1]heptanes and the reactions of epoxides of endo‐amides are accompanied by intramolecular cyclization and completed by the formation of N‐[aryl(alkyl, cycloalkyl)]‐exo‐2‐hydroxy‐4‐azatricyclo[4.2.1.0^3,7]nonanes. The structures and stereochemical homogenity of the products have been confirmed by the analysis of ¹H and ¹³C NMR spectra, correlation spectroscopy, and nuclear Overhauser enhancement spectroscopy experiments. We discuss the behavior of epoxides and provide an analysis of the coefficients of the atomic orbitals in the molecular orbital–linear combination of atomic orbitals equation (AM1 method). © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:119–130, 2001     

Reduction of tri(hetero)arylcarbinols to tri(hetero)arylmethanes

Summary A series of seven new tri(hetero)arylmethanes has been prepared by reduction of the corresponding carbinols using a mixture of lithium aluminium hydride/aluminium trichloride. The yields are excellent (77–98%) except in the case of the tri(2-benzothienyl)derivative (41%).¹H NMR spectra are discussed.

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Reduktion von Tri(hetero)arylcarbinolen zu Tri(hetero)arylmethanen

Zusammenfassung Durch die Reduktion der entsprechenden Carbinole mit Lithium-aluminiumhydrid/Aluminiumchlorid wurden sieben neue Tri(hetero)arylmethane in sehr guten Ausbeuten (77–98%) hergestellt. Eine Ausnahme bildet das Tri-(2-benzothienyl)-Derivat mit 41%. Die¹H-NMR-Spektren werden diskutiert.

     

Preparation of halogen-modified titanium(II) arene complexes and their electronic spectra

Summary Complexes of overall formula TiAl₂X₈ · Ar (X = Cl, Br or I, Ar = benzene or hexamethylbenzene) and the complexes containing various amounts of Br or I in addition to Cl were prepared both by a direct synthesis — the reduction of titanium tetrahalide by aluminium in the aromatic solvent and in excess of the corresponding aluminium halide — and by halogen exchange between the complexes and aluminium halides. The interpretation of the electronic spectra of the complexes is given on the assumption of pseudooctahedral symmetry of the ligand field. The values of 10 Dq and B obtained are compatible with the assignment.     

Hydride atomization in graphite furnace atomizers

Summary A new type of graphite furnace atomizer — the graphite paper atomizer (GPA) — is described. The tube dimensions are large: l=92 mm, i.d.=9 mm. Analytical determinations of hydride forming traces were carried out in the absence and in the presence of hydride forming matrices using both a normal quartz tube atomizer (QTA) and the new GPA. The analyticalk results for pure solutions of the traces are the same for both atomizers. In the presence of hydride forming matrices the GPA gave improvements of 1 to 3 orders of magnitude for GPA. Chemical matrix modifications were employed to reduce matrix interferences of Se, Te (with Cu²⁺ ions) and Bi (with EDTA). It was possible to explain the types of interference by hydride forming elements. Thermodynamic calculations were made of the equilibrium composition in hydride vapours. The influence of temperature and hydrogen on the atomization in both atomizers has been studied. The AsSb molecule could be detected spectroscopically in appropriate hydride vapours.It was concluded that the main source of matrix interference by hydride forming matrices is the formation of diatomic molecules of the AsSb type between trace and matrix elements. At higher temperatures (about 2000–2300 K) the thermal atomization of the hydrides plays the main role.

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Hydridatomisierung in Graphitrohratomisatoren

Zusammenfassung Ein neuer Typ eines Graphitrohratomisators — der Graphitpapieratomisator (GPA) — wird beschrieben. Die Rohrdimensionen dieses Atomisators sind relativ groß: l=92 mm, i =9 mm. Analytische Bestimmungen von hydridbildenden Spuren wurden durchgeführt in Abwesenheit und in Gegenwart von hydridbildenden Matrices. Dabei wurde sowohl ein normaler Quarzrohratomisator als auch der neue Graphitpapieratomisator eingesetzt. Die analytischen Resultate waren, wenn nur reine Lösungen eingesetzt wurden, für beide Atomisatoren gleich. In Gegenwart von hydridbildenden Matrices ergaben sich jedoch für den Graphitpapieratomisator analytische Verbesserungen von 1–3 Größenordnungen. Chemische Matrixmodifikation wurde eingesetzt zur Verminderung der Matrixeinflüsse von Se, Te (durch Cu²⁺-Ionen) und von Bi (durch EDTA). Die Mechanismen der Störungen durch hydridbildende Matrices konnten geklärt werden. Thermodynamische Berechnungen der Gleichgewichtszusammensetzung in Hydrid-Dämpfen wurden ausgeführt. Verschiedene Experimente werden beschrieben zum Studium des Einflusses der Temperatur und des Wasserstoffs auf die Atomisierung von Hydriden in beiden Atomisatoren. Das AsSb-Molekül konnte auf spektroskopischem Wege in entsprechenden Hydrid-Dämpfen nachgewiesen werden. Die Schlußfolgerungen aus diesen Berechnungen und Experimenten sind:Der Hauptgrund für die Matrixeffekte hydridbildender Matrices ist die Bildung von zweiatomigen Molekülen zwischen Spur und Matrixelement. Bei höheren Temperaturen (2000–2300 K) spielt die thermische Atomisierung der Hydride die Hauptrolle.

     

Studies and microdetermination of some organic sulfur functions by reduction with titanium(III) sulfate solution

Micromethods are described for the determination of organic sulfoxides and disulfides based on reduction with titanium (III) sulfate solution, the excess of which is titrated with standard ferric alum as usual. The procedures developed depended on the nature of the compound whether aromatic or aliphatic. Quantitative reduction of sulfoxides was achieved in presence of ammonium thiocyanate and sodium acetate but whereas aryl sulfoxides required heating at 70 °C for 30 minutes, the alkyl members demanded heating at 90 °C for one hour. Complete reduction of disulfides was possible in presence of acetate buffer and heating at 50 °C for 15 minutes for aromatic disulfides and at 80 °C for 30 minutes in case of the aliphatic ones. a Calculated by dividing the total titer in a ratio of 2:12. b Calculated using the total titer consumed. Sulfonyl halides, thiocyanates, and isothiocyanates do not react with the titanium(III) solution. The effect of the various sulfur functions on the determination of the nitro group with titanium(III) was also studied and various nitro-substituted sulfur compounds were successfully analyzed.     

On acidification of thiols to produce the corresponding disulfides

Thiophenol 1 , 2‐mercaptobenzimidazole ( 3a ), 4,5‐diphenylimidazole‐2‐thione 3b , and 5‐mercapto‐2‐aryl‐1,2,4‐s‐triazoles ( 6a–b ) are chemically oxidized using the acidified acetic acid method to the corresponding disulfides 2, 5a–b and 7a–b , respectively. The structures of the disulfides thus formed were established both chemically and by spectral analysis. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 16:399–402, 2000     

Study on the production of formaldehyde-14C by direct reduction of14CO2 with LiAlH4

A vial technique was developed for the synthesis of formaldehyde-¹⁴C from¹⁴CO₂ in an ether solution of lithium aluminium hydride. The yield of formaldehyde (40–50%) was achieved by optimization of the reaction parameters.     

Determination of toxic and non-toxic arsenic species in urine by microwave assisted mineralization and hydride generation atomic absorption spectrometry

Flow injection — microwave oven — hydride generation — atomic absorption spectroscopy (FI-MO-HG-AAS) has been optimized for the determination of the total and toxic arsenic in urine with and without persulfate, respectively. With microwave oven assisted digestion of urine with 5% (w/v) K₂S₂O₈ and 5% (w/v) NaOH all arsenicals completely can be converted to arsenate, which is determined by HG-AAS to give the total concentration of the six species present in urine. The detection limits of 4–6 g l^–1, the relative standard deviation of 3–7% and the high sample throughput make the methods suitable for rapid routine on-line determination. Application of the proposed procedures to the analysis of urine from people on a diet rich in seafood revealed a significant increase in total urinary arsenic due to the rapid excretion of organoarsenicals. Efficient decomposition and quantitative recovery of all arsenic species in spiked urine is achieved by using 5% K₂S₂O₈ in 5% NaOH at 4.6 ml min^–1, microwave power of 700 W and a 1.5 m coil.     

Unusual oxidative dehydration of vic-[alkyl(aryl)thio]-substituted aromatic (heteroaromatic) carboxamides

A new procedure was developed for the synthesis of nitriles of vic-[alkyl(aryl)sulfonyl] derivatives of benzoic, anthraquinonecarboxylic, and 4-isothiazolecarboxylic acids by the reactions of the corresponding vic-[alkyl(aryl)thio]-substituted aromatic (heteroaromatic) carboxamides with chlorine in organic solvents containing 20—65% of water. Oxidative dehydration of 1-(butylthio)anthraquinone-2-carboxamide afforded 1-butyl-6,11-dihydro-3H-1⁴-anthra[2,1-d]isothiazole-3,6,11-trione 1-oxide as a by-product. The structure of the latter was established by X-ray diffraction analysis. The reaction scheme involving the formation of S-chlorosulfonium chlorides followed by their hydrolysis was proposed.     

Fluorimetric determination of aluminium in water by sequential injection through column extraction

A fluorimetric procedure for the determination of aluminium with matrix removal in drinking water is proposed. The system is based both on the solid phase extraction of aluminium on a new chelating resin (XAD-4 modified by grafting salicylic acid) and the fluorimetric detection of a complex formed between 8-hydroxyquinoline-5-sulfonic acid (HQS) and Al(III), after elution of the resin by hydrochloric acid. The sorption and elution of aluminium were studied in both competitive and non-competitive conditions, varying pH, flow-rates, volume and concentration of reagents, as well as time contact. The optimised procedure allows determination of Al³⁺ at the sub-ppb level (LOD: 0.2 g L^–1 for 1 ml of sample) within a working range of 0.2–500 g L^–1. The analytical procedure was successfully employed for the determination of aluminium in drinking water during and after flocculation/coagulation treatment processes.     

Oxidation of aminothiols by molecular oxygen catalyzed by copper ions. Stoichiometry of the reaction

Catalysis of oxidation of aminothiols by copper ions was studied depending on the structure of aminothiols and pH of the medium. The catalytic reaction proceeds in the inner coordination sphere of Cu⁺. At pH 7—9, oxidation of bidentate aminothiols involves reduction of O₂ to H₂O₂. At pH 9—13, oxidation of chelating aminothiols is accompanied by reduction of O₂ to H₂O, whereas oxidation of weak-chelating aminothiols still proceeds by the former mechanism. In this process, the thiolate anions coordinated to the Cu⁺ ions lose one electron each and are oxidized to amino disulfides, which go from the inner sphere of the Cu⁺ complex into a solution. Procedures developed for the determination of amino disulfides, the chemiluminescence determination of H₂O₂ in the presence of aminothiols as luminescence quenchers, and a modified polarographic procedure for the determination of O₂ allowed us to establish that oxidation of aminothiols is not accompanied by catalytic decomposition of H₂O₂ that formed.     

Cross-section TEM for examinations of selective tungsten CVD for via hole filling

The reaction between tungsten layers [deposited by chemical vapor deposition (CVD) as well as by physical vapor deposition (PVD)] and an aluminium alloy (AlSi) has been investigated. For CVD tungsten layers deposited on AlSi by silane reduction of WF₆ the formation of an aluminium fluoride interlayer has been established by cross-section transmission electron microscopy (XTEM). At the interface between PVD-W and AlSi, an intermetallic compound may be formed depending on the thermal treatment. A crystalline intermediate layer has been found after annealing at 400°C (twice for 30 min), whereas an interface between as deposited double layers showed no interlayer. For all samples investigated, diffusion of aluminium into the tungsten layer was observed. The diffusion depth depends on the heat treatment and the tungsten morphology. Intermediate layers — if they exist — limit the diffusion but do not act as a diffusion barrier.     

Cleavage ofβ -propiothiolactones with methanesulfenyl chloride and acetyl sulfur chloride

-Propiothiolactones are cleaved at the S-CO bond by methanesulfenyl chloride and acetyl sulfur chloride to form mixed disulfides — derivatives of the acid chlorides of -mercapto-isobutyric acid. The mixed disulfides readily disproportionate on heating under acid or base catalysis conditions to give the corresponding symmetrical disulfides. A convenient method was found for obtaining the previously hard-to-obtain symmetrical disulfides.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 475–478, April, 1972.     

Efficient synthesis of chiral β-and γ-N-tosylaminoalcohols from 1-aryl-2-aminopropane-1,3-diols

(1S,2S)-1-Aryl-2-tozylaminopropan-1-ols were synthesized by cyclization of 1-aryl-2-aminopropane-1,3-diol to aryl(1-tosylaziridin-2-yl)methanols, followed by hydride reduction of the latter. Reduction of the aza-Payne rearrangement products of intermediate aryl(1-tosylaziridin-2-yl)methanols gave (1S)-1-aryl-3-tosylaminopropan-1-ols. Published in Zhurnal Organicheskoi Khimii, 2006, Vol. 42, No. 4, pp. 514–518. The text was submitted by the authors in English.