Effective synthesis of novel O-acetylated compounds over ZrO2-Al2O3 solid acid

The solid acids such as ZrO₂, Al₂O₃ and ZrO₂-Al₂O₃ containing different ZrO₂ loadings (10–80 mol%) were prepared by solution combustion method (SCM) and characterized for their total surface acidity by NH₃-TPD/n-butylamine back titration method and crystallinity by powder X-ray diffraction (PXRD) technique. These solid acids were evaluated for their catalytic activity in the synthesis of novel O-acetylated products from substituted phenols, pyridine alcohols and aryl alcohols with acetic anhydride (AA) as an acetylating agent. The reaction conditions were optimized by varying the catalyst, molar ratio of the reactants, reaction temperature and amount of the catalyst. All the solid acids used in this study exhibited good catalytic activity in the reaction. In particular, ZrO₂-Al₂O₃ containing 80 mol% of ZrO₂ was found to be highly active in the acetylation reaction with high yield of acetylated products. Triangular correlation between the surface acidity, crystallinity and catalytic activity of solid acids was observed. These solid acids were found to be reactivable and reusable.     

Enantioselective synthesis of (2S,3′R,7′Z)-N-(3′-hydroxy-7′-tetradecenoyl)-homoserine lactone

A concise enantioselective total synthesis of (2S,3′R,7′Z)-N-(3′-hydroxy-7′-tetradecenoyl)-homoserine lactone is described. Key feature of this protocol is a catalytic asymmetric hydrogenation and a prophenol-zinc-catalyzed diazo addition to imine reaction as genesis of chirality. Moreover, flexibility is built in the synthesis to generate enantioenriched analogs using catalytic amount of enantioenriched C₂-symmetric ligands.     

Ruthenium-catalyzed cyclization of 3-en-1-ynyl imines with nucleophiles via tandem 5-exo-dig cyclization and nucleophilic addition

Treatment of 3-en-1-ynyl imines with TpRuPPh₃(CH₃CN)₂PF₆ catalyst (1 mol %) in DCE (50 °C, 6 h) effected catalytic cyclization with suitable nucleophiles and gave functionalized pyrroles in good yields. The reaction mechanism is proposed to proceed via (2-pyrrolyl)carbenoid intermediates derived from 5-exo-dig cyclization. This catalytic reaction works well with various nucleophiles, including water, alcohols and anilines.     

Chemo- and diastereoselective Bi(OTf)3-catalyzed benzylation of silyl nucleophiles

The direct alkylation of silyl enol ethers with para-methoxybenzylic alcohols or their corresponding acetates was efficiently catalyzed by Bi(OTf)₃ in CH₃NO₂ as the solvent. The reaction provided the α-benzylated carbonyl compounds in high yields after short reaction times using 1-2.5 mol % of the catalyst. Benzylic acetates other than para-methoxybenzylic acetates also underwent the reaction. High facial diastereoselectivities were observed with acetates derived from chiral α-branched para-methoxybenzylic alcohols. In addition, a catalytic reduction with Et₃SiH as the reducing agent is reported.     

A new catalytic system for the copolymerization of dicyclopentadiene with CO: PdCl2/phen/M(CF3SO3)n

A new three-component catalytic system, PdCl₂/phen/M(CF₃SO₃)_n, was studied in the copolymerization of dicyclopentadiene (DCPD) with CO. It was found that the PdCl₂/phen/CF₃SO₃H catalytic system gave a very low catalytic activity, and the PdCl₂/phen/M(CF₃SO₃)_n catalytic system exhibited high activity when M(CF₃SO₃)_n was introduced instead of CF₃SO₃H. The resultant cooligomer was analyzed using various techniques such as FT-IR, ¹H NMR, ¹³C NMR, DSC and TGA. The results indicated that the copolymer was a polyspiroketal (PS) of CO and DCPD. Due to the tension of the ring of DCPD, the degree of copolymerization is low and the degree of crystallinity is also not high. The effects of ligands, M(CF₃SO₃)_n, solvents, 1,4-benzoquinone/PdCl₂ molar ratio, and temperatures on the copolymerization have been discussed in detail. The results showed that this novel catalytic system exhibited highly efficient activity, especially when 1,10-phenanthroline (phen) was used as ligand and Cu(CF₃SO₃)₂ was used as cocatalyst. The corresponding reaction rate was 49 000 g PS/molPd h when the reaction was carried out at 60 °C and 3.0 MPa of CO. The weight average molecular weight (M_w) and the number average molecular weight (M_n) of the resultant cooligomer were 1180 g/mol and 564 g/mol, respectively.     

Regioselective ring-opening of epoxides with ortho-lithioanisoles catalyzed by BF3·OEt2

It is presented that a number of o-2-hydroxyalkylanisoles could be efficiently synthesized through the regioselective ring-opening reaction of epoxides with o-lithioanisoles in the presence of BF₃·OEt₂ Lewis-acid catalyst. Sterically demanding o-lithioanisoles had to be generated by exploiting the combination of ⁿBuLi and a catalytic amount of TMEDA (0.20 equiv) in Et₂O as the lithiator whereas ‘normal’ anisole could be lithiated at ortho-position by treatment with ⁿBuLi in THF as usual. Surprisingly, the availability of THF and a catalytic amount of TMEDA (0.20 equiv) in the reaction mixture was found to enhance the reaction yields dramatically. A complex aggregate formation by the co-operative ligation of THF and TMEDA to ortho-lithioanisole(s) was proposed to rationalize the high reactivity achieved in the ring-opening reaction of epoxides.     

A new strategy of tandem transetherification-intramolecular hetero Diels-Alder reaction with (E,Z)-mixture of ethyl 2-nitro-3-ethoxyacrylate and δ,ε-unsaturated alcohols leading to functionalized trans-fused bicyclic nitronates

Tandem reaction of (E,Z)-ethyl 2-nitro-3-ethoxyacrylate (E:Z=25:75) with δ,ε-unsaturated alcohols leading to functionalized trans-fused bicyclic nitronates as single stereoisomers in high yields has been developed under thermal condition and in the presence of a catalytic amount of a Lewis acid catalyst such as Yb(OTf)₃. This process involves the configurational control of transetherified intermediates under a rapid, reversible transetherification reaction pathway for affording stereoselective trans-fused cyclic nitronates as single stereoisomers in intramolecular hetero Diels-Alder reaction.     

Synthesis of 4a-carba-β-l-lyxofuranose, 4a-carba-β-l-arabinofuranose and 2,2,5-trimethyl-3a,6a-dihydro-cyclopenta[1,3]dioxol-4-one using Mn/CrCl3 mediated domino reactions and ring closing metathesis

A common method for the synthesis of 4a-carba-β-l-lyxofuranose and 4a-carba-β-l-arabinofuranose from d-mannose and 2,2,5-trimethyl-3a,6a-dihydro-cyclopenta[1,3]dioxol-4-one from d-ribose is described using catalytic Nozaki-Hiyama-Kishi (NHK) conditions and ring closing metathesis (RCM). In this transformation, ω-deoxy-ω-iodo manno/ribo furanoside undergoes reductive elimination in the presence of Mn/CrCl₃ to give the corresponding olefin-aldehyde which was trapped by nucleophile under the same conditions to afford the desired diolefinic species. The ring closing metathesis reaction on these diolefinic species with Grubbs second generation catalyst produced the required carbocycles.     

InCl3 as an efficient catalyst for synthesis of oxazolines under thermal, ultrasonic and microwave irradiations

Efficient synthesis of 2-oxazolines by the reaction of nitriles with β-aminoalcohols using InCl₃ as catalyst under reflux conditions is reported. This catalyst can be successfully applied to the chemoselective conversion of dicyanobenzenes to their corresponding mono- and bis-oxazolines. The application of ultrasonic and microwave irradiation improved the yields and reduced the reaction times. Another advantage of this catalytic system is its ability to carry out large-scale reactions under ultrasonic and MW irradiations. Alkylnitriles such as acetonitrile was also converted to its corresponding 2-methyloxazoline in the presence of catalytic amounts of InCl₃.     

rac-BINAP-PdCl2 catalyzed Heck reactions of 3-formylquinolin-2-yl chlorides with methyl acrylate: synthesis of methyl 3-(3-formylquinolin-2-yl) acrylates

rac-BINAP-PdCl₂ catalytic system catalyzed Heck reaction of 3-formylquinolin-2-yl chlorides with methyl acrylate in DMA is described to the synthesis of methyl 3-(3-formyl-quinolin-2-yl)-acrylates, in good to excellent yields. The reaction could be also extended with other activated alkenes to afford Heck products. Fused-benzene ring in heterocyclic and carbocyclic moieties was found to enhance the yields.     

Synthesis,spectroscopic characterization,X-ray crystal structure,biological screening and catalytic studies of organotin(IV) carboxylates of 3-(4-cyanophenyl) acrylic acid

A series of six organotin(IV) carboxylates [Me₂SnL₂] (1), [n-Bu₂SnL₂] (2), [n-Oct₂SnL₂] (3), [Me₃SnL] (4), n-Bu₃SnL (5) and [Ph₃SnL] (6), where L = 3-(4-cyanophenyl) acrylic acid have been synthesized and characterized by elemental analysis, FT-IR and NMR (¹H, ¹³C). The complex (4) was also analyzed by single crystal X-ray analysis which showed distorted trigonal bipyramidal geometry with polymeric bridging behavior. The complexes 1–6 were screened for antimicrobial activities and cytotoxicity. The results showed significant activity with few exceptions. The catalytic activity of complexes was assessed in transesterification reaction of Brassica campestris oil (triglycerides) to produce biodiesel (fatty acid methyl esters). The results showed that triorganotin(IV) complexes exhibited good catalytic activity than their di-analogues.     

3-Iodo-4-chalcogen-2H-benzopyran as a convenient precursor for the sonogashira cross-coupling: synthesis of 3-alkynyl-4-chalcogen-2H-benzopyrans

3-Iodo-4-chalcogen-2H-benzopyran derivatives underwent a direct Sonogashira cross-coupling reaction with several terminal alkynes in the presence of a catalytic amount of Pd(PPh₃)₂Cl₂ with CuI as a co-catalyst, using Et₃N as base and solvent. This cross-coupling reaction proceeded cleanly under mild conditions and was performed with propargylic alcohols, propargylic ethers, as well as alkyl and aryl alkynes, furnishing the correspondent 3-alkynyl-4-chalcogen-2H-benzopyrans in good yields.     

An Efficient Approach to 2-CF3-Indoles Based on ortho-Nitrobenzaldehydes

The catalytic olefination reaction of 2-nitrobenzaldehydes with CF₃CCl₃ afforded stereoselectively trifluoromethylated ortho-nitrostyrenes in up to 88% yield. The reaction of these alkenes with pyrrolidine permits preparation of α-CF₃-β-(2-nitroaryl) enamines. Subsequent one pot reduction of nitro-group by Fe-AcOH-H₂O system initiated intramolecular cyclization to afford 2-CF₃-indoles. Target products can be prepared in up to 85% yields. Broad synthetic scope of the reaction was shown as well as some followed up transformations of 2- CF₃-indole.     

A quantum chemical study on the mechanism of chiral N-oxides-catalyzed Strecker reaction

The mechanism for the Strecker reaction of silyl cyanide (H₃SiCN) and benzaldehyde N-methylimine (PhCHNCH₃) catalyzed by chiral 3,3′-dimethyl-2,2′-bipyridine N,N′-dioxide was investigated using the density functional theory (DFT) at the B3LYP/6-31G* level. The calculations revealed that the non-catalyzed reaction proceeded in a concerted way via a five-membered ring transition state, while the catalytic one occurred stepwisely via a hexacoordinate hypervalent silicate intermediate. It was predicted that both non-catalyzed and catalytic Strecker reactions involved two competitive reaction pathways, that is, addition followed by isomerization or isomerization followed by addition. The calculations indicated that two reaction pathways were comparable for both non-catalyzed and catalytic Strecker reactions. In the catalytic reaction, the strong electron donor (N-O) of chiral N-oxide played an important role in enhancing the reactivity and nucleophilicity of H₃SiCN by coordinating O atom to the Si atom of H₃SiCN. Chiral N-oxide could be used as a good catalyst for the reaction, which was in agreement with the experimental observations.     

Hydroesterification of styrene using an in situ formed Pd(OTs)2(PPh3)2 complex catalyst

Hydroesterification of styrene to 3-phenyl propionate 1, and 2-phenyl propionate 2, has been studied using a Pd(OTs)₂(PPh₃)₂ catalyst formed in situ from Pd(OAc)₂, PPh₃ and p-toluenesulfonic acid (p-tsa). Because of the weakly coordinating properties of the TsO⁻ ligand, the catalyst has vacant coordination sites capable of easy activation of reactants. The presence of water is found to be necessary for the reaction and hydrogen enhances the catalytic activity under certain conditions (with Pd:p-tsa=1). The beneficial effect of hydrogen, p-tsa and water is discussed in terms of favoring the formation of a Pd–H species, which initiates the catalytic cycle through the insertion of styrene into this bond with formation of a Pd-alkyl intermediate, which inserts CO to give a Pd-acyl intermediate, which, upon nucleophilic attack of the alkanol on the carbon atom of the acyl ligand, yields the final product and the starting hydride back to the catalytic cycle. p-tsa would favor the formation of a Pd–H species by reactivating any Pd(0) species that may form during the course of catalysis. Water would favor the formation of a Pd–H species through a reaction closely related to the water–gas shift reaction. The effect of various ligands, promoters, solvents and alcohols on catalytic activity as well as selectivity pattern has been studied. Regioselectivity to the branched product, 2, increases with decrease in basicity of the phosphorous ligands as well as steric bulk around the palladium center and polarity of the medium.     

Influence of chromium modification on the properties of MnOx-FeOx catalysts for the low-temperature selective catalytic reduction of NO by NH3

Catalytic properties of MnO_x-FeO_x complex oxide (hereafter denoted as Mn-Fe) catalysts modified with different loadings of chromium oxide were investigated by using the combination of physico-chemical techniques, such as N₂ physisorption, X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), in situ Fourier transform infrared spectroscopy (in situ FT-IR) and temperature-programmed reduction (TPR) and their catalytic activities were evaluated with the selective catalytic reduction (SCR) of NO_x by NH₃. It was found that with the addition of Cr, more NO could be removed in the low-temperature window (below 120 °C). Among the tested catalysts, Mn-Fe-Cr (2 : 2 : 1) catalyst exhibited the best catalytic performance at 80 °C with the NO conversion higher than 90%. The combination of the reaction and characterization results indicated that (1) the strong interaction among tertiary metal oxides existed in the catalysts when Cr was appropriately added, which made the active components better dispersed with less agglomeration and sintering and the largest BET specific surface area could be obtained; (2) Cr improved the low-temperature reducibility of the catalyst and promoted the formation of the active intermediate (–NH⁺₃), which favored the low-temperature SCR reaction.     

Nd(OTf)3-catalyzed intramolecular-intermolecular cascade cyclization reaction: An access to phenanthro[9,10-b]furan derivatives

An intramolecular-intermolecular cascade cyclization reaction via multi metal-carbene intermediates has been developed. This reaction uses catalytic amount of Nd(OTf)₃, which actives both alkyne and aldehyde moieties. This protocol provides a novel strategy for the synthesis of phenanthro[9,10-b]furans.     

Synthesis,structure, and catalytic activity of rare-earth metal amides with a neutral pyrrolyl-functionalized indolyl ligand

<正>1 Representation of complexes and selected bond distances and bond angles Figure S1 Structure of complex 4. Hydrogen atoms were omitted for clarity, ellipsoids set at the 30% probability level. Selected bond distances() and angles(°): Er(1)–Cl(1) 2.6180(18), Er(1)–N(1) 2.301(6), Er(1)–N(4) 2.232(6), Er(1)–N(5) 2.229(6), N(1)–Er(1)–Cl(1) 87.41(14), N(4)–Er(1)–Cl(1) 101.16(14), N(5)–Er(1)–Cl(1) 118.60(16), N(4)–Er(1)–N(1) 114.1(2), N(5)–Er(1)–N(1) 108.7(2), N(5)–Er(1)–N(4) 121.9(2).Figure S2 Structure of complex 5. Hydrogen atoms were omitted for clarity, ellipsoids set at the 30% probability level. Selected bond distances(o) and angles(°): Y(1)–Cl(1) 2.6212(12), Y(1)–N(1) 2.280(3), Y(1)–N(4) 2.214(3), Y(1)–N(5) 2.228(3), N(1)–Y(1)–Cl(1) 87.67(8), N(4)–Y(1)–Cl(1) 121.32(8), N(5)–Y(1)–Cl(1) 102.88(8), N(4)–Y(1)–N(1) 107.75(11), N(5)–Y(1)–N(1) 111.64(11), N(4)–Y(1)–N(5) 120.78(10).     

Stereoselective synthesis of α-glucosides from 3-O-propargyl protected glucal exploiting the alkynophilicity of AuCl3

The stereoselective synthesis of 2,3-unsaturated α-d-glucosides by the S_N2′ addition of diverse aglycones onto 4,6-di-O-benzyl-3-O-propargyl glucal was achieved using a catalytic quantity of AuCl₃. The Au catalyzed reaction was explored using various aliphatic, aromatic, alicyclic and monosaccharide aglycones. The current protocol tolerates diverse functional groups and is highly stereoselective, fast, catalytic and mild.     

PbS nanoparticles stabilized on HPG-modified FeNi3 as catalyst for synthesis of 2-amino-4H-chromene under mild conditions

FeNi₃\SiO₂\HPG\PbS magnetic nanoparticles (MNPs) catalyst was readily prepared from inexpensive starting materials in aqueous media which catalyzed the synthesis 2-amino-4H-chromene via intermittent microwave irradiation. X-ray diffraction, transmission electron micrographs, and scanning electron micrographs were employed to characterize the properties of the synthesized FeNi₃\SiO₂\HPG\PbS MNPs. High catalytic activity and ease of recovery from the reaction mixture using external magnet and several reuse times without significant losses in performance are additional eco-friendly attributes of this catalytic system.