A synthon for a 14-electron Ir(iii) species: catalyst for highly selective β-(Z) hydrosilylation of terminal alkynes

A synthon for a 14-electron Ir(iii) species is described. The geometrical control exerted by the ligand system over the Ir-alkenyl intermediate in hydrosilylation of terminal alkynes precludes formation of the more thermodynamically stable β-(E)-vinylsilane, thus affording the β-(Z) isomer in excellent yields.     

Supported catalysts based on Pd–In nanoparticles for the liquid-phase hydrogenation of terminal and internal alkynes: 1. formation and structure

The formation of Pd–In catalysts synthesized from the heteronuclear acetate complex PdIn(CH₃COO)₅ was studied by temperature-programmed reduction, electron microscopy, IR spectroscopy of adsorbed CO and hydrogen temperature-programmed desorption (H₂-TPD). IR spectroscopy of adsorbed CO and H₂-TPD confirmed the formation of bimetallic Pd–In nanoparticles. It was found that the Pd–In nanoparticle surface contains predominantly Pd atoms separated from one another by indium atoms, which is evidenced by the disappearance of the CO band shift resulting from the lateral dipole–dipole interaction between adsorbed CO molecules and by a significant decrease in the band intensity of CO adsorbed in bridged form. Almost complete inhibition of palladium hydride (PdH_x) provides additional evidence of the formation of Pd–In bimetallic particles.     

A highly selective method for the synthesis of(E)-α-methyl-α,β-unsaturated aldehydes

Anhydrous acidic treatment of E,Z mixtures of α-methyl-α,β-unsaturated imines followed by hydrolysis gives the corresponding aldehydes with ≥ 100:1 E:Z ratios.     

Xphos ligand and platinum catalysts: A versatile catalyst for the synthesis of functionalized β-(E)-vinylsilanes from terminal alkynes

Hydrosilylation of functionalized terminal arylalkynes with a variety of silanes catalyzed by PtCl₂ or PtO₂ in the presence of the air-stable and bulky Xphos ligand was investigated. Regardless of the electronic nature (electron withdrawing or donating group) and the position (o, m, p) of the substituents on the aromatic ring, a single β-(E)-styrylsilanes was obtained in good to excellent yields. The regioselectivity of the H-Si bond addition was found to be governed by steric effects induced by the bulky Xphos ligand. A dramatic regioselectivity was also observed when functionalized terminal aliphatic alkynes were employed as a substrate and in these cases regioisomeric β-(E)-vinylsilanes were generated with excellent selectivity.     

Direct synthesis of α-hydroxyketone phosphates from terminal alkynes and H-phosphine oxides in the presence of PhI(OAc)_2 and H_2O

A simple and highly efficient one-pot method for the construction of α-hydroxyketone phosphates from terminal alkynes and H-phosphine oxides has been developed in the presence of PhI(OAc)_2 and H_2O.The present protocol provides an attractive approach to α-hydroxyketone phosphates in good to high yields,with the advantages of operation simplicity,the use of commercially available materials,broad substrate scope,high atom efficiency and good tolerance to scale-up synthesis.     

Supported catalysts based on Pd–In nanoparticles for the liquid- phase hydrogenation of terminal and internal alkynes: 2. catalytic properties

Pd–In/Al₂O₃ and Pd–In/MgAl₂O₄ catalysts prepared from dinuclear Pd–In acetate complexes were studied in the hydrogenation of alkyne compounds with different structures. The Pd–In catalysts demonstrate high selectivity in the hydrogenation of internal alkynes comparable with that of the Lindlar catalyst. Similar activity/selectivity characteristics are reached at a significantly lower Pd content. For terminal alkynes, the favorable effect of Indium introduction is considerably less pronounced. An analysis of the In effect on the selectivity and the ratio between the rates of the first and second hydrogenation steps suggests that the reaction selectivity is determined to a large extent by a thermodynamic factor (adsorption–desorption equilibrium between the reactants and the reaction products).     

Highly efficient synthesis of (R)- and (S)-piperazic acids using proline-catalyzed asymmetric α-hydrazination

The highly efficient synthesis of (R)- and (S)-piperazic acids, components of naturally occurring antibiotic cyclodepsipeptides, was achieved in 80% overall yield by the use of a proline-catalyzed asymmetric α-hydrazination as the key step.     

(S)-(−)-α-Methylbenzylamine as an efficient chiral auxiliary in enantiodivergent synthesis of both enantiomers of N-acetylcalycotomine

(S)-(−)-α-Methylbenzylamine 2 was used as a chiral auxiliary in the enantiodivergent synthesis of simple isoquinoline alkaloids. The prochiral imine moiety in compound 4 was reduced with different reagents, giving diastereomeric amines 5a or 5b, which subsequently were transformed to either (S)-(−)-N-acetylcalycotomine 6 or (R)-(+)-N-acetylcalycotomine ent-6 in good enantiomeric excess. ¹⁹F NMR of its Mosher's acid ester was used to establish the purities of final compounds.     

Highly enantioselective synthesis of (+)- and (−)-perfluoroalkyl(aryl) homoallyl alcohols

Asymmetric allylboration of perfluoroaldehydes and fluorine substituted aromatic aldehydes with ^dIpc₂BAll and 2-Icr₂BAll has been investigated. Both enantiomers of the fluorinated homoallyl alcohols were obtained in high yields and excellent enantiopurity (95–99% ee).     

Studies on ZnBr2-mediated synthesis of axially chiral aryl-substituted allenes from terminal alkynes,aromatic aldehydes and (S)-α,α-diphenylprolinol

The studies on the ZnBr₂-mediated synthesis of axially chiral aryl-substituted allenes from terminal alkynes, aromatic aldehydes, and commercially available chiral amine (S)-α,α-diphenylprolinol were conducted. Axially chiral aryl-substituted allenes can be obtained in moderate yields with up to 96% ee.     

Enantioselective synthesis of (S)- and (R)-α-methylserines: application to the synthesis of (S)- and (R)-N-Boc-N,O-isopropylidene-α-methylserinals

This report describes the synthesis of enantiomerically pure (S)- and (R)-α-methylserines on a multigram scale, starting from the Weinreb amide of 2-methyl-2-propenoic acid and using a stereodivergent synthetic route that involves a Sharpless asymmetric dihydroxylation reaction. As a synthetic application of these quaternary α-amino acids, they were used as starting materials in the synthesis of the well-known valuable homochiral (S)- and (R)-N-Boc-N,O-isopropylidene-α-methylserinal building blocks.     

Metal-free,one-pot highly selective synthesis of (E)-vinyl sulfones and sulfoxides via addition–oxidation of thiols with alkynes

We have developed a highly selective one-pot method for the synthesis of (E)-vinyl sulfones and sulfoxides from thiols with terminal alkynes. The sulfones and sulfoxides could be obtained with excellent selectivity in good isolated yields. It is simple, efficient and environmentally benign, and metal-free. The mechanism for the formation of the (E)-vinyl sulfones was also proposed.     

A practical and efficient synthesis of (E)-β-aryl-α,β-unsaturated amides

In this paper, we report a one-step convergent synthesis of (E)-β-monosubstituted α,β-unsaturated amides 3 from α-sulfonyl acetamide 1 and benzyl bromide derivatives 2.     

Cerium(Ⅳ) ammonium nitrate catalysed facile and efficient synthesis of polyhydroquinoline derivatives through Hantzsch multicomponent condensation

A general and convenient practical approach for the synthesis of polyhydroquinoline derivatives has been achieved via one-pot four-component Hantzsch condensation of aromatic aldehydes,dimedone,ethyl acetoacetate and ammonium acetate in the presence of a catalytic amount of cerium(Ⅳ)ammonium nitrate (CAN),in ethanol solvent at ambient temperature.Simple work-up, mild reaction conditions,inexpensive and non-toxic catalyst,and excellent product yields are the advantageous features of this method.     

Optimization of polyacrylonitrile-cysteine resin synthesis and its selective removal of Cu(Ⅱ) in aqueous solutions

Polyacrylonitrile beads(PAN) cysteine(CS) was synthesized from polyacrylonitrile beads(PAN) and cysteine(CS).The content of the functional group and the percentage conversion of the functional group of PAN-CS prepared under the optimum condition using response surface methodology(RSM) for the first attempt were 3.22 mmol/g and 35.78%.The structure was characterized by ET-IR and elemental analysis.The adsorption properties of the resin for Cu(Ⅱ) were investigated by batch and column experiments.Batch adsorption results suggested that PAN-CS had higher adsorption capability for Cu(Ⅱ)than other metal ions and maximum saturated adsorption capacity was 184.7 mg/g.The resin and its metal complexes were studied by FT-IR.Furthermore,the resin can be eluted easily using 1 mol/L HC1.PAN-CS can provide a potential application for selective removal of copper from waste solution.     

An efficient synthesis of (Z)-α-fluorochalcones via the palladium-catalyzed cross-coupling reaction of (Z)-α-fluorocinnamoyl chloride with boronic acids

An efficient synthesis of α-fluorochalcones (1,3-diphenyl-2-fluoroprop-2-en-1-one) based on the Suzuki–Miyaura palladium-catalyzed cross-coupling reaction of arylboronic acids with α-fluorocinnamoyl chlorides in the presence of Cs₂CO₃ in toluene is described. This approach allows the synthesis of fluorinated analogues of functionalized natural chalcones.     

The synthesis of (R)- and (S)-α-trifluoromethyl-α-hydroxycarboxylic acids via enzymatic resolutions

Kinetic resolution of 1,1,1-trifluoro-2-alkanone cyanohydrin acyl derivatives with Candida rugosa lipase afforded the remaining (R)-enantiomer in high selectivity (E from 30 to >200). Candida rugosa lipases from several suppliers were compared and found to differ remarkably in their selectivity. The (R)-enantiomer was hydrolyzed in one step to yield optically pure (R)-α-trifluoromethyl-α-hydroxycarboxylic acids in excellent yield. The (S)-acids were obtained in good e.e. by subtilisin-catalyzed resolution of the corresponding racemic esters followed by chemical hydrolysis of the remaining (S)-esters.     

Organomanga+nese (II) reagents XIV1: A short and efficient synthesis of diastereoisomeric (±)-α-bisabolols and (±)-chlorphenoxamine

Diastereoisomeric (±)-α-bisabolols (7), a sesquiterpenoid alcohol, and (±)-chlorphenoxamine (12), an antihistamine, have been prepared in excellent yields, Both these short and convenient syntheses involve as a key step the one-pot elaboration of a dissymmetrical tertiary alcohol via an organomanganese reagent (5 to 7 and 9 to 10 respectively).     

Gallium(III)-catalysed bromocyanation of alkynes: regio- and stereoselective synthesis of β-bromo-α,β-unsaturated nitriles

Treatment of arylacetylenes and cyanogen bromide in ClCH(2)CH(2)Cl with a catalytic amount of GaCl(3) afforded (Z)-β-bromoacrylonitriles with high regio- and stereoselectivity.     

Two efficient and green methods for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) without use of any catalyst or solvent

Two efficient and green methods for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) without use of any catalyst or solvent have been developed simply by heating (at 120°C) or microwave irradiation (300 W) of intimate mixtures of 3-methyl-l-phenyl-5-pyrazolone and aldehyde in 2:1 mole ratio.