Cinchona Alkaloid‐Catalyzed Enantioselective Direct Aldol Reaction of N‐Boc‐Oxindoles with Polymeric Ethyl Glyoxylate

The first enantioselective direct aldol addition of N‐Boc‐oxindoles to polymeric ethyl glyoxylate is presented. The reaction is performed by using as low as 0.1 mol% (DHQ)₂PHAL and gives access to α‐hydroxycarboxylate derivatives bearing adjacent secondary alcohol and quaternary stereocenters with high levels of diastereo‐ and enantiocontrol. The use of ethyl glyoxylate in its polymeric form represents an important advantage for synthetic applications and allows us to directly install a C₂ unit ready to be converted in useful building blocks. A further one‐pot protection/deprotection sequence catalyzed by Zn(ClO₄)₂⋅6 H₂O preserved the α‐hydroxycarboxylates from racemization by means of a parasitic alcohol‐catalyzed retroaldol reaction.     

The Hydroamination of methyl acrylates with amines over zeolites

H-form zeolites, H-FAU and H-BEA have been studied as heterogeneous catalysts for the hydroamination. They catalyzed the reaction of methyl acrylate with aniline to give N-[2-(methoxycarbonyl)ethyl]aniline (1) as a main product. H-BEA and H-FAU zeolites efficiently catalyzed the hydroamination to afford anti-Markovnikov adduct as a main product. The conversion of aniline around 55–85% was achieved within 18 h over H-BEA and H-FAU zeolites with SiO₂/Al₂O₃ molar ratio of 25–30; however, the formation of N,N-bis[2-(methoxycarbonyl)ethyl]aniline (2) as a product of double addition of methyl acrylate to aniline has also been observed as a by-product over H-BEA and H-FAU catalysts. The influences of the reaction parameters such as temperature and catalyst amount, and type of α,β-unsaturated esters and amines have been also investigated.     

Nano ZrP2O7 Catalyzed Multicomponent Reaction for an Easy Access of 4H-pyrans and 1,4-dihydropyridines

ZrP₂O₇ nanoparticle catalyzed one-pot synthesis of 4H-pyran scaffolds installing a one-pot three-component coupling reaction of an aldehyde, malononitrile, and ethyl acetoacetate. Also the synthesis of 1,4-dihydropyridines was investigated by using aldehydes, ethyl acetoacetate and ammonium acetate as utilizing nano structured ZrP₂O₇ as an efficient catalyst in ethanol. The attractive features of this process are mild reaction conditions, reusability of the catalyst, short reaction times, easy isolation of the products, and excellent yields.     

Reaction of arylidenehydrazono-4-aryl-2,3-dihydrothiazole-5-carbonitriles with diethyl acetylenedicarboxylate. Synthesis of (Z)-ethyl 2-[((Z)-2-(E)-arylidenehydrazono)-4-oxo-thiazolidine-5-ylidene]acetates. NMR investigation

(Z)-Ethyl 2-[((Z)-2-(E)-arylidenehydrazono)-4-oxo-thiazolidine-5-ylidene]acetates were synthesized by three different methods: (a) reaction of arylidenehydrazono-4-aryl-2,3-dihydrothiazole-5-carbonitriles with diethyl acetylenedicarboxylate (DEAD) in acetic acid with prolonged reflux, (b) reaction between thiosemicarbazones, 2-arylidenemalononitriles and DEAD under conventional conditions or microwave irradiation, (c) one-pot three-component reaction of thiosemicarbazone derivatives, ylidene and DEAD. The thiazolinone adducts were obtained in good to excellent yields. NMR of the obtained products was investigated.     

Lipase-catalyzed esterification of citronellol with lauric acid in supercritical carbon dioxide/co-solvent media

Direct esterification of citronellol and lauric acid catalyzed by immobilized lipase B from Candida antarctica was performed in supercritical carbon dioxide with different organic solvents and ionic liquids serving as co-solvents. The highest concentration of citronellol laurate after 1 h of reaction performance (3.95 mmol/g substrates) was obtained in SC CO₂ with ethyl methylketone serving as a co-solvent. The optimal temperature and pressure for citronellol laurate synthesis in SC CO₂/EMK medium was determined to be 60 °C and 10 MPa.     

Preparation of rapeseed oil esters of lower aliphatic alcohols

Rapeseed oil esters with lower aliphatic alcohols (C₁−C₄) were prepared in simple batch mode using an alkali (KOH) or acid (H₂SO₄) catalyst. The transesterification reaction conditions were optimized in order to obtain high yields of esters of the quality defined by standards for biodiesel fuels and for a short reaction time. Under these conditions it was possible to prepare only the methyl and ethyl esters catalyzed by KOH. Propyl and butyl esters were obtained only under acid catalysis conditions. The reaction catalyzed by H₂SO₄ was successfully accelerated using slightly higher catalyst concentrations at the boiling points of the alcohols used. The branched-chain alcohols reacted more slowly than their linear homologs, while t-butanol did not react at all. It was also possible to transesterify rapeseed oil using a mixture of alcohols characteristic of the end products of some fermentation processes (e.g., the acetone-butanol fermentation). A simple calculation was made which showed that, because of the higher price of longer-chain alcohols and because of the more intensive energy input during production the esters of these alcohols, they are economically unfavorable as biodiesel fuels when compared with the methyl ester.     

Comparison of the reactivities of 2-mercaptoaniline and 2-hydroxyaniline with 2-chloronicotinoyl chloride

The reaction between equimolar 2-chloronicotinoyl chloride and 2-mercaptopyridine in ClCH₂CH₂Cl, after 30 minutes refluxing in ClCH₂CH₂Cl solution, produced pyrido[2,3,b][1,5]benzothiazepin-5(H)one 7, and 6-[3-(2-benzothiazolyl)pyridin-2-yl)thio]-N-[3-(2-benzothiazolyl)pyridin-2-yl]aniline 8. In contrast, the reaction using the same reaction conditions between equimolar 2-chloronico- tinoyl chloride and 2-hydroxypyridine, produced the simple amide, 2-chloro-N-(2-hydroxyphenyl) nicotinamide 9. 2-Chloro-N-(2-mercaptophenyl)nicotinamide was considered to be a common intermediate in the formation of 7 and 8. The characterizations of 7–9 were achieved by X-ray crystallography. The conformations of 7 and 8 in the solid state can be described as “U” and “V”-shaped, respectively.     

Nickel‐Catalyzed Regio‐ and Stereoselective Reductive Coupling of Oxa‐ and Azabicyclic Alkenes with Enones and Electron‐Rich Alkynes

A nickel‐catalyzed regio‐ and stereoselective reductive coupling of oxa‐ and azabicyclic alkenes with activated alkenes and electron‐rich alkynes is described. Thus, 7‐oxabenzonorbornadienes underwent reductive coupling with various vinyl ketones such as ethyl, methyl, propyl and α‐methyl‐substituted vinyl ketones, in the presence of a nickel(II) iodide (NiI₂), zinc (Zn), and water catalyst system in acetonitrile at 50 °C for 14 h to afford 2‐alkylnaphthalenes in good to excellent yields. Under similar reaction conditions, 7‐azabenzonorbornadiene derivatives provided cis‐2‐alkyl‐1,2‐dihydronaphthalene derivatives in high yields. On the other hand, the nickel(II) iodide, tris(4‐fluorophenyl)phoshine [P(4‐FC₆H₄)₃] and zinc catalyst system successfully catalyzed the reductive coupling reaction of electron‐rich alkynes, with 7‐aza‐ and 7‐oxabenzonorbornadienes to give cis‐2‐alkenyl‐1,2‐dihydronaphthalene derivatives in good to excellent yields. In the reaction, a mild reducing agent (zinc) and simple hydrogen source (water) were used.

     

Asymmetric Glyoxylate-Ene Reactions Catalyzed by Chiral Pd(II) Complexes in the Ionic Liquid [bmim][PF6]

The room temperature ionic liquid [bmim][PF₆] was employed as the reaction medium in the asymmetric glyoxylate-ene reaction of α-methyl styrene (4a) with ethyl glyoxylate using chiral palladium(II) complexes as the catalysts. [Pd(S-BINAP)(3,5-CF₃-PhCN)₂](SbF₆)₂ (1b) showed the highest catalytic activity. Under the reaction conditions of 40 °C, 0.5 h, and 1b/4a molar ratio of 0.05, ethyl α-hydroxy-4-phenyl-4-pentenoate was obtained in excellent chemical yield (94 %) with high enantioselectivity (70 %). Other α-hydroxy esters can also be obtained in high chemical yields and enantioselectities through the glyoxylate-ene reactions of alkenes with glyoxylates catalyzed by 1b in [bmim][PF₆]. Moreover, the ionic liquid [bmim][PF₆] which contained the palladium(II) complex could be recycled and reused several times without significant loss of the catalytic activity.     

Lipase made active in hydrophobic media by coupling with polyethylene glycol

Lipases from various microorganisms were chemically modified with polyethylene glycol derivatives: 2,4-bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine (activated PEG₂, a chain-shaped polymer) and copolymer of polyoxyethylene allyl methyl diether and maleic anhydride (activated PM, a comb-shaped polymer). Because each polymer is amphipathic, the modified lipases become soluble not only in aqueous solution but also in hydrophobic media. They exhibit potent catalytic actions for ester synthesis and ester exchange reactions, the reverse reaction of hydrolysis, in transparent organic solvents and also in oily substrates without organic solvents. With PEG₂-lipases, macrocyclic lactone and gefarnate (geranyl farnesylacetate) were synthesized in high yields from 16-hydroxy-hexadecanoic acid ethyl ester and from farnesylacetic acid and geraniol in organic solvents, respectively. The modified lipase catalyzed the esterification preferentially with the (R)-isomer of secondary alcohols. Because the ester synthesis reactions with modified lipase proceeded in the transparent benzene system, the kinetic parameters (Michaelis constant and maximum velocity) were obtained by reciprocal plotting according to the Michaelis equation. With comb-shaped polymer as modifier, PM-lipase catalyzed effectively the reverse reaction of hydrolysis in organic solvents. The properties of each modified lipase are discussed in relation to those of the nonmodified lipase. Presented at the 84th Annual Meeting of the American Oil Chemists' Society held on April 25–29, 1993, in Anaheim, CA.     

Investigation on the Esterification of Fatty Acids Catalyzed by the H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> heteropolyacid

In this work, the H₃PW₁₂O₄₀ heteropolyacid (HPW) was employed as a homogeneous catalyst to promote the efficient esterification (ethanolysis) of a number of saturated and unsaturated fatty acids (myristic, palmitic, stearic, oleic, and linoleic) under mild reaction conditions. HPW showed a similar activity to those observed for p-toluene sulfonic acid (PTSA) and sulfuric acid (H₂SO₄), the other acidic catalysts we compared them with in this study. In the HPW-catalyzed esterification of stearic acid, the addition of water caused a remarkable decrease in the ethyl stearate yields. On the other hand, the increase in the HPW concentration (up to a maximum value) promoted a proportional improvement in the oleic acid to ethyl oleate conversion. Kinetic measurements using oleic acid as a prototype substrate revealed that the esterification reactions catalyzed by HPW, H₂SO₄, and PTSA are of first-order in relation to the fatty acid concentration. Finally, the catalytic activity of HPW remained unaltered even after several recovery/reutilization cycles whereas the tungsten content in the final product (biodiesel produced by the HPW-catalyzed esterification of oleic acid) was found to be at an acceptably low level (0.0095 mg of W per g of biodiesel).     

Ring transformation and cyclization reactions of 1,1-dioxo-1,2-thiazines – syntheses of pyridines and benzo[c]thiazines with new substitution pattern

In presence of ammonia/ammonium acetate the 3,5-dimethyl-2-phenyl-1,1-dioxo-1,2-thiazine-4-carbaldehyde ( 1 ) reacts with ethyl cyanoacetate to the ethyl 2-cyano-4-[1-methyl-2-methylthio-2-(N-phenylsulfamoyl)vinyl)-hexa-2,4-dienoate] ( 3 ) and the Knoevenagel condensation product 4-(2-ethoxycarbonyl-2-cyanovinyl)-3,5-dimethyl-6-methylthio-1,1-dioxo-2-phenyl-2H-1,2-thiazine ( 2 a). The 4-(2,2-dicyanovinyl)-3,5-dimethyl-6-methylthio-1,1-dioxo-2-phenyl-2H-1,2-thiazine ( 2b ) is obtained from 1 and malononitril. The masked 1,5-dicarbonyl compound 2a undergoes ring transformation to the 3-cyano-1,6-dimethyl-5-[1-methylthio-2-(N-phenylsulfamoyl)vinyl]pyridin-2-one ( 5 ) with methylamine. With ethanolic ethoxide the condensation products 2a,b afford the 7-amino-6-ethoxycarbonyl-4-methylthio-2,2-dioxo-1-phenyl-benzo[c]1,2-thiazine ( 6a ), respectively the corresponding 6-cyano derivative 6b , while 3 cyclizises to furnish ethyl 2-amino-6-methyl-5-[1-methyl-2-methylthio-2-(N-phenyl-sulfamoyl)vinyl]nicotinate ( 4 ).     

Synthesis and characterization of copolymers with alternating 1,4-bis(5'-acetyl-2'-thienyl)benzene or 1,3-bis(5'-acetyl-2'-thienyl)benzene chromophore and disiloxane units

Summary Activated (Ph₃P)₃RuH₂CO (Ru) catalyzed copolymerization of 1,4-bis(5'-acetyl-2'-thienyl)benzene (I) and 1,3-divinyltetramethyldisiloxane (II) yields alt-copoly[3,3,5,5-tetramethyl-4-oxa-3,5-disila-1,7-heptanylene/2',2"-diacetyl-5',5"-(1,4-benzene)-3',3"-bis (thiophenylene)] (III). On the other hand, Ru catalyzed copolymerization of 1,3-bis(5'-acetyl-2'-thienyl)benzene (IV) and II fails. Nevertheless, Ru catalyzed reaction of IV with excess vinylpentamethyldisiloxane (V) yields 1,3-bis(4'-pentamethyldisiloxy-ethyl-5'-acetyl-2'-thienyl)benzene (VI). VI undergoes acid catalyzed siloxane equilibration polymerization to give alt-copoly[3,3,5,5-tetramethyl-4-oxa-3,5-disila-1,7-heptanylene/2',2"-diacetyl-5',5"-(1,3-benzene)-3',3"-bis(thiophenylene)] (VII) and hexamethyldisiloxane. Copolymers III and VII have been characterized. Received: 26 July 1999/Revised version: 12 October 1999/Accepted: 12 October 1999     

Ligand Controlled Highly Selective Copper‐Catalyzed Borylcuprations of Allenes with Bis(pinacolato)diboron

Copper‐catalyzed highly selective borylcuprations of allenes with bis(pinacolato)diboron produce two different types of alkenylboranes by applying a ligand effect. In the presence of tris(para‐methoxyphenyl)phosphine [P(C₆H₄OMe‐p)₃], the reaction of aryl‐1,2‐dienes affords 2‐alken‐2‐yl boronates as the only product with exclusive Z‐geometry; the regioselectivity is switched to afford the 1‐alken‐2‐yl boronates as the major products when the bidentate phosphine 2,2′‐bis(diphenylphosphino)biphenyl is used as the ligand.     

Transfer hydrogenation and transfer hydrogenolysis: XII. Selective hydrogenation of fatty acid methyl esters by various hydrogen donors

The selective hydrogenation of methyl linoleate was studied using various organic compounds as hydrogen sources in the presence of homogeneous and metallic palladium catalysts. Complete selectivity to monoenes and relatively little formation of isolatedtrans double bonds were realized by the hydrogen transfer from L-ascorbic acid at 47% conversion of starting material to hydrogenation products. The hydrogenation bytrans-1,2-cyclohexanediol catalyzed by RuH₂(PPh₃)₄ also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH₂(PPh₃)₄, also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH₂(PPh₃)₄, the presence of these hydroxy compounds increased the isomerization of methyl elaidate tocis-monoenes.     

Sonochemical synthesis of 3-methyl-4-arylmethylene isoxazole-5(4H)-ones by amine-modified montmorillonite nanoclay

Ultrasound irradiation was applied for the rapid and clean synthesis of 3-methyl-4-arylmethylene isoxazole-5(4H)-ones through condensation of hydroxylamine hydrochloride, ethyl acetoacetate and benzaldehyde derivatives. This methodology was effectively catalyzed by amine functionalized montmorillonite K10 nanoclay (NH₂-MMT). Compared with conventional methods, this protocol has promising features for the reaction response such as shorter reaction times, easier work-up, ease of separation of pure product with high yields and simplicity in the experimental procedure.     

Update: An Efficient Synthesis of Poly(ethylene glycol)‐Supported Iron(II) Porphyrin Using a Click Reaction and its Application for the Catalytic Olefination of Aldehydes

The facile synthesis of polyethylene glycol (PEG)‐immobilized iron(II) porphyrin using a copper‐catalyzed azide‐alkyne [3+2] cycloaddition “click” reaction is reported. The prepared complex 5 (PEG‐C₅₁H₃₉FeN₇O) was found to be an efficient catalyst for the selective olefination of aldehydes with ethyl diazoacetate in the presence of triphenylphosphine, and afforded excellent olefin yields with high (E) selectivities. The PEG‐supported catalyst 5 was readily recovered by precipitation and filtration, and was recycled through ten runs without significant activity loss.     

Heterogeneous Enantioselective Synthesis of a Dihydropyran Using Cu-Exchanged Microporous and Mesoporous Materials Modified by Bis(oxazoline)

The formation of dihydropyran from the Diels–Alder reaction between E-ethyl-2-oxo-3-pentenonate and vinyl ethyl ether is investigated using copper (II) bis(oxazoline) as catalyst. The homogeneously and heterogeneously catalyzed reactions are contrasted. Immobilization using mesoporous materials (Cu-MCM-41, Cu-AlSBA-15, Cu-MSU-2) and zeolite Y is found to produce an effective heterogeneous catalyst. Although the level of enantioselection is not high in this initial study, the CuH-zeolite Y/bis(oxazoline) catalyst gives the highest ee (41% ee), which is significantly higher than that observed for the Cu(OTf)₂ homogeneous catalyst (20% ee) under comparable conditions. In addition, with the heterogeneously catalyzed reaction, the enantioselection changes from the initial 2R,4S product to the 2S,4R diastereoisomer. This behavior is not observed with the homogeneously catalyzed reaction, which always yields the 2R,4S product. These results are discussed in terms of the confinement of the catalyst complex within the pores of the heterogeneous catalyst.     

Upgrading of Lignin-Derived Compounds: Reactions of Eugenol Catalyzed by HY Zeolite and by Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Abstract  

The conversion of eugenol (4-allyl-2-methoxyphenol), a compound derived from the lignin in woody biomass, was catalyzed by HY zeolite at 573 K and atmospheric pressure. The main products were isoeugenol and guaiacol, formed by isomerization and by deallylation, respectively. Substituted guaiacols with saturated side-chains (4-methylguaiacol, 4-ethylguaiacol, and 4-propylguaiacol) were also formed, by hydrogen transfer and alkylation reactions. The pseudo-first-order rate constant for the overall disappearance of eugenol was found to be 12.4 L (g of catalyst)/h. When the catalyst was Pt/γ-Al₂O₃ used in the presence of H₂, significant hydrogenation of the propenyl side-chain took place, accompanied by isomerization, and hydrodeoxygenation. Under similar operating conditions, the reaction catalyzed by Pt/γ-Al₂O₃ in the presence of H₂ gave a higher eugenol conversion (X = 0.70) than the reaction catalyzed by HY zeolite (X = 0.11), primarily because of the dominant hydrogenation observed with the former catalyst. In the absence of H₂ as a co-reactant, the acidic γ-Al₂O₃ support in Pt/γ-Al₂O₃ evidently catalyzed all the classes of reactions catalyzed by HY zeolite.     

Study of thermal and dyeing behavior of isotactic polypropylene fiber graft copolymerized with acrylate monomers using preirradiation method

In an attempt to modify isotactic polypropylene (IPP) fiber, grafting of acrylate monomers such as methyl acrylate (MA) and ethyl acrylate (EA) onto IPP has been carried out by preirradiation method in aqueous medium. Percentage of grafting has been determined as a function of various reaction parameters. Rate of grafting (R_g) and induction period (I_p) have been evaluated as a function of total initial monomer concentration. Methyl acrylate was found to be more reactive than ethyl acrylate toward grafting. Thermogravimetric analysis (TGA) indicates that the thermal stability of polypropylene fiber is significantly improved upon grafting. While polypropylene fiber could not be dyed by crystal violet, the grafted fiber was dyed with crystal violet, and the dye uptake has been quantitatively determined by spectrometric method. © 1994 John Wiley & Sons, Inc.