A biomimetic synthesis of (−)-ascorbyl phloroglucinol and studies toward the construction of ascorbyl-modified catechin natural products and analogues

A method for appending the ascorbyl moiety onto the framework of phenolic natural products has been developed. This reaction proceeds in two steps from l-ascorbic acid and employs acetic acid catalysis. Excellent stereoselectivity is observed during C-C bond formation between the phenolic compound and dehydroascorbic acid, and the process is also chemoselective for phenol derivatives bearing electron-donating substituents in each of the 1, 3, and 5 positions. Further, good regioselectivity was also observed when phenols lacking an axis of C₂ symmetry were employed. This method has led to the synthesis of (−)-ascorbyl phloroglucinol as well as the tetracyclic core of ascorbyl-modified catechin natural products.     

NiCl2-catalyzed cascade reaction of isocyanides with functionalized anilines

A NiCl₂-catalyzed isocyanide insertion reaction of anilines bearing another nucleophile functional group utilizing TEMPO as oxidant in isopropyl ethanoate (IPA) or THF has been reported. This simple and general method could afford 2-aminobenzimidazole, 2-aminobenzothiazole, 2-aminobenzoxazole, as well as 2-aminobenzo[d][1,3]oxazine in moderate to excellent yields (up to 95% yield).     

Oxidative Coupling of 1,3-Dicarbonyl Compounds by Cerium(IV) Ammonium Nitrate

A fast, mild, and highly efficient method for the intermolecular coupling of 1,3-dicarbonyl compounds using cerium ammonium nitrate in CH₃CN/CH₃OH/H₂O has been described. The procedure provided a convenient method for the synthesis of 1,4-diketone derivatives with excellent yields (up to 96%) and powerful evidence for the oxidation mechanism mediated by cerium ammonium nitrate.     

Catalytic activity of Ru/Fe2O3, obtained by adsorption of ruthenium on iron oxide supports

The effect of the method of a support preparation on its adsorption properties for ruthenium from solution and on the catalytic properties of Ru/Fe₂O₃ catalysts obtained by adsorption, has been studied. Moreover, the influence of the solvent in which a given ruthenium compound was dissolved on the properties of Ru/Fe₂O₃ catalysts was observed.     

Nano ceria catalyzed synthesis of α-aminophosphonates under ultrasonication

A simple, efficient and general method has been developed for the one-pot three component syntheses of α-aminophosphonates. The condensation of aldehyde, amine and triethyl phosphite by employing CeO₂ nanoparticles as catalyst gave α-aminophosphonates. The catalyst showed good recyclability. Nano CeO₂ has been found to be an excellent catalyst for the green synthesis of α-aminophosphonates under ultrasound irradiation and solvent-free condition. The α-aminophosphonates are obtained in good to excellent yield. This catalyst provides cleaner conversion, short reaction time and high selectivity which makes the protocol feasible and economical attractive.     

Synthesis and comparative study of catalytic activity between Pd-metallodendrimer and Pd/Cu-bimetallodendrimer nanoparticle-based on triazine

Triazine-based heterogeneous Pd/Cu-bimetallodendrimer Nanoparticle (Pd/Cu-BMDNP) has been synthesized by sequential loading method from palladium containing metallodendrimer (Pd-MD) which was prepared by the reaction of 2,4,6-Triamine-1,3,5-triazine (melamine) with substituted benzoyl chloride using (Ph₃P)₂PdCl₂ in DMSO at 90 °C. SEM and EDX of Pd/Cu-BMDNP showed the nanosized aggregated spherical surface morphology and the presence of Palladium and copper of the NP. Also, the phase was detected as Face Centered Cubic (FCC) structure by XRD analysis. In addition, the average particle size of Pd/Cu bimetallic catalyst was identified as 12–13 nm by TEM investigation. Greater thermal stability of Pd/Cu-BMDNP than Pd-MD was detected from TG and DSC experiments. The Pd-metallodendrimer has been also characterized by IR, ¹H NMR, ¹³C NMR, SEM, EDX, Mass, TG and DSC techniques. The simple recoverability, high reusability, low amount of catalyst loading, negligible amount of catalyst leaching of the heterogeneous Pd/Cu-BMDNP have made more effective catalyst than homogeneous Pd-metallodendrimer for the C–C cross-coupling reaction such as Heck, Glaser, Sonogashira and Suzuki-Miyaura in excellent yields.     

Synthesis of Six-Membered Functionalized Carbocyclic Compounds by One-Pot Reaction of Hydroquinone Derivatives and Dienes

A general method for one-pot reaction of hydroquinone derivatives and dienes has been developed. The system of Pb₃O₄ in tetrahydrofuran–trifluoroacetic acid was found to play dual roles as oxidant for the generation of quinones in situ and as catalyst for the Diels–Alder cycloaddition, which makes the one-pot reaction efficient and easy to carry out. Using this method, a variety of six-membered functionalized carbocyclic compounds can be easily prepared in medium to excellent yields at room temperature.      

Palladium‐catalyzed cyanation reaction of aryl halides using K4[Fe(CN)6] as non‐toxic source of cyanide under microwave irradiation

An efficient method for preparation of aryl nitriles—using [Pd{C₆H₂(CH₂CH₂ NH₂)‐(OMe)₂,3,4} (µ‐Br)]₂ complex as an efficient catalyst and K₄[Fe(CN)₆] as a green cyanide source—from aryl bromides, aryl iodides and aryl chlorides under microwave irradiation has been reported. This complex has been demonstrated to be an active and efficient catalyst for this reaction. Using a catalytic amount of this synthesized palladium complex in DMF at 130 °C led to production of the cyanoarenes in excellent yields in short reaction times. Copyright © 2010 John Wiley & Sons, Ltd.     

Ruthenium-Catalyzed Coupling Reaction of Benzylic Halides

Abstract

Reported herein is a novel method on dechlorination coupling reaction of halides by using RuCl₂(PPh₃)₃ catalyst under a hydrogen atmosphere with benzene as the solvent, which affords alkanes in excellent yields.     

A green-chemistry approach for the efficient synthesis of triazolo benzoxazepines or triazolo benzodiazepines in aqueous micellar system

A convenient route for the synthesis of triazole fused benzoxazepines or benzodiazepines in aqueous micellar medium has been described. The two step one-pot synthesis involves Sonogashira reaction of prop-2-ynyl 2-azidobenzoates and aryl iodides followed by intramolecular azide–alkyne cyclization using Pd(CH₃CN)₂Cl₂ as catalyst and ethanedial,1,2-bis(2-methyl-2-phenylhydrazone) as ligand, under atmospheric condition. The method excludes the use of copper salts as catalyst as well as hazardous organic solvents.     

Die Dimerisierung von Di(n-butyl)fluorphosphan und seine Reaktion mit Benzaldehyd

The Dimerization of Di(n-butyl)fluorophosphane and its Reaction with Benzaldehyde The phosphorus atom of organylfluorophosphanes possesses electrophilic as well as nucleophilic properties. This dualistic character decisively determines both their disproportionation and their reaction with aldehydes. The phoshanylphoshorane n-Bu₂P? PF₂(n-Bu)₂, 1 b , has been proved to be the intermediat product of the disproportionation of n-Bu₂PF. In the presence of an equimolar amount of Et₃N an equilibrium exists between 1 b and the monomeric n-Bu₂PF. n-Bu₂PF react with benzaldehyde forming the phosphinitophoshorane n-Bu₂P′? O? CHPh? PF₂(n-Bu)₂, 3 a. Reliable information on the reaction pathway has been obtained by means of crossing experiments.     

Clean and atom-economic synthesis of octahydroacridines: application to essential oil of citronella

A green and efficient method for the synthesis of octahydroacridine (OHA) has been developed by a simple one-pot hetero-Diels-Alder reaction starting from (+)-citronellal and N-arylamines in the presence of a solid supported catalyst (SiO₂/ZnCl₂), under MW irradiation and without any solvent. The method was used in the direct preparation of OHA from citronella oil in good yield.     

Oxidation of o‐phenylenediamine to 2,3‐diaminophenazine in the presence of cubic ferrites MFe2O4 (M = Mn,Co, Ni,Zn) and the application in colorimetric detection of H2O2

Metal ferrites nanocrystallites, MFe₂O₄ (M = Mn, Co, Ni, Zn) were prepared by coprecipitation method and characterized by a combination of physico‐chemical and spectroscopic techniques. MFe₂O₄ nanoparticles having particle size in the range 10–35 nm were tested as catalysts in the oxidation of o‐phenylenediamine (OPD) to 2,3–diaminophenazine (DAP) using hydrogen peroxide as oxidant at room temperature. Kinetic data was collected for the catalytic oxidation of OPD to DAP by monitoring the UV–vis absorbance at 415 nm and fit well to the Michaelis–Menten model yielding kinetic parameters K_m (Michaelis–Menten constant) and V_max (maximum rate of reaction). MnFe₂O₄ nanoparticles provide the highest catalytic activity in the oxidation of OPD to DAP at room temperature. A colorimetric method was developed based on the MnFe₂O₄/OPD system for the detection of H₂O₂ in reaction solution. The method has a detection limit of 30 μM for H₂O₂ and wide linear range.     

Stereocontrolled synthesis of hydroxyethylamine isosteres via chiral sulfoxide chemistry

A novel synthesis of enantiopure hydroxyethylamine isosteres 1 has been developed. Reaction of lithiated β-sulfinylethylamines 3 with N-Cbz-imines generated in situ from α-amino-sulfones 4 afforded in good to excellent yields and moderate stereocontrol the 2-sulfinyl-1,3-diamines 2. The latter were submitted to the nonoxidative Pummerer reaction (NOPR) in CH₂Cl₂, that produced the target compounds 1 in very good yields with inversion of configuration. In some cases, the use of acetonitrile as solvent resulted in a double-inversion pathway, leading for example to the oxazolidinone 5. The total synthesis of an epimer of Saquinavir has been achieved by this method.     

Copper‐Assisted/Copper‐Free Synthesis of Functionalized Dibenzo[b,f]oxepins and Their Analogs via a One‐Pot Tandem Reaction

A simple, convenient, and efficient method for the formation of functionalized dibenzo[b,f]oxepins and their analogs bearing both electron‐donating and electron‐withdrawing groups has been developed via a one‐pot cascade reaction. Most starting materials are commercially available 2‐(2‐hydroxyphenyl)acetonitriles and 2‐haloarylaldehydes. The procedure makes use of Cs₂CO₃ as the base, and DMF as solvent under copper‐assisted/copper‐free conditions. The reaction has a comprehensive group tolerance for substrates. Most of the reactions were complete within 1 h in good‐to‐excellent yields, and the reaction temperatures were relatively low. The protocol could be scaled up to grams without lowering the yield. A reaction mechanism was also proposed.     

Efficient,Iron-Catalyzed Synthesis of 2-Mercaptobenzothiazole Through S-Arylation/Heterocyclization of 2-Haloaniline with Potassium Xanthate

A mild and practical method for the synthesis of 2-mercaptobenzothiazole has been developed by using iron as an efficient catalyst. The present tandem reaction process allows access to a wide range of 2-mercaptobenzothiazoles in good to excellent yields by the reaction of 2-haloaniline with potassium O-ethyl dithiocarbonate in the presence of FeF₃ as a catalyst and 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl as a ligand under an atmosphere of argon.     

Green synthesis of (−)-isopulegol from (+)-citronellal: application to essential oil of citronella

A simple green and efficient method has been developed for the synthesis of (−)-isopulegol from (+)-citronellal in the presence of a solid supported catalyst (SiO₂/ZnCl₂), under solvent-free conditions and MW irradiation. It was also found that the same technology is applicable to the direct preparation of (−)-isopulegol from the essential oil of citronella (Cymbopogon nardus, growing in southern Brazil) in excellent yield.     

TiO2-coated graphene oxide-molybdate complex as a new separable nanocatalyst for the synthesis of pyrrole derivatives by Paal-Knorr reaction

The preparation of chemical and pharmaceutical compounds through organic reactions has always been associated with the production of environmental waste. Growth population and concerns about ecological pollution increase the interest in using heterogeneous solid catalysts with capabilities such as increasing reaction efficiency and reducing the production of by-products, as well as the ability to separate and reuse. To develop and benefit such catalysts as much as possible, in this study, using graphene oxide (GO) as a support, we succeeded in preparing a heterogeneous catalyst with a high contact surface, excellent performance, and recyclability. Graphene oxide nanosheets were synthesized according to Hummer’s method. hexamolybdate anions ([n-Bu₄N]₂[Mo₆O₁₉]) were placed on this support as a catalytically active site using linkers. The structure of this catalyst was confirmed by XRD, FT-IR, EDS, SEM, TEM, TGA, Raman, and nitrogen adsorption–desorption analyses, and it was used to produce pyrroles by the Paal-Knorr method. The performance of the synthesized nanocatalyst was satisfactory for all the derivatives studied. Recovery and reuse of GO@TiO₂@(CH₂)₃N = Mo[Mo₅O₁₈] after catalytic reactions were examined. This catalyst could be quickly recovered by simple filtration and recycled ten times without significant loss of its catalytic activity.     

Metal sulfide: An efficient promoter for the synthesis of 2-mercaptobenzothiazoles from 2-haloanilines and carbon disulfide

A convenient method has been developed for the preparation of a variety of 2-mercaptobenzothiazoles from 2-haloanilines and CS₂ mediated by metal sulfide. In this reaction, 2-haloanilines reacted with CS₂ in the presence of Na₂S?·?9H₂O to form 2-mercaptobenzothiazoles. Na₂S?·?9H₂O functioned both as an activator of CS₂ and as a base. Furthermore, NMR analysis was used to identify the different reaction mechanisms of 2-haloanilines and CS₂ mediated by Na₂S or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), which demonstrated that Na₂S interacted only with CS₂, while DBU reacted with both 2-iodoaniline and CS₂.     

Carbon black supported PtCu nanoparticles derived from mix-phased Cu precursor for high-performanced oxygen reduction reaction in acid medium

Alloying high-cost Pt with transition metals has been considered as an effective route to synthesize the electrocatalysts with low Pt loading and excellent activity towards oxygen reduction reaction (ORR) under acid solution. The galvanic replacement method, as featured with efficiency and simplicity, is widely reported to produce Pt-based bimetallic alloys and thereby declare the significance of reductive transition metal precursor on the enhancement of ORR performance. Herein, mix-phased Cu−Cu₂O precursor was applied to prepare carbon black supported highly dispersed PtCu alloy nanoparticles (PtCu/C). The proper Cu−Cu₂O ratios can exactly facilitate the generation of small sized PtCu alloy nanoparticles with regulated bimetallic content. Meanwhile, the Cu₂O phase is revealed to benefit the electron transfer from Pt to Cu and thus improve the intrinsic activity of Pt active sites. And the metallic Cu can favor the promotion of electrochemical active surface area. Consequently, the as-prepared PtCu/C behaves impressive ORR activity with half-wave potential of 0.88 V (vs. RHE) and mass activity of 0.49 A cm⁻² mg_Pt⁻¹ at 0.8 V, which is 9.8 times of commercial Pt/C catalysts. Our work will offer helpful advices for the development and regulation of novel Pt-based alloy materials towards diverse electrocatalysis.