磷改性Cr2O3/Al2O3催化4-乙基酚转化制轻质芳烃

以烷基酚转化为轻质芳烃（苯和甲苯）为目标，制备了Cr₂O₃/Al₂O₃催化剂，并以4-乙基酚为模型化合物研究了其加氢反应性能。体积空速、氢油比、反应压力和温度升高时，脱烷基率、芳烃总选择性、轻质芳烃选择性呈先增大后减小的趋势，反应温度对转化率影响较大。以不同浓度磷酸对Cr₂O₃/Al₂O₃进行改性，随着磷酸用量的增大，催化剂酸量总体增大，主要是弱酸和中强酸，酸强度先增加后降低，磷酸用量较高时，弱酸增加幅度较大。与未改性相比，质量分数8%磷酸改性Cr₂O₃/Al₂O₃上4-乙基酚转化率99.5%，脱烷基率提升9.4%，达74.4%，轻质芳烃选择性提高4.0%，达到57.0%，以较高选择性实现了转化制轻质芳烃，同时，芳烃总选择性高达80.4%，较高程度保持了芳环不被破坏。提出了Cr₂O₃/Al₂O₃上4-乙基酚加氢反应的路径并对反应机理进行了研究。     

Synthesis, characterization, and reactivity of ruthenium diene/diamine complexes including catalytic hydrogenation of ketones

Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an excess of N,N,N',N'-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd, 1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II) precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N',N'-tetraethylethylene diamine (teeda) resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N-H functionalities in the coordinated diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod, amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective.     

有机磷化合物的研究 XXV: 溶剂性质对烯丙在膦酸酯碳阴离子和芳醛反应区域选择性的影响

本文研究烯丙基膦酸二乙酯碳阴离子和苯甲醛, 对甲基苯甲醛的反应, 考察了溶剂对反应区域选择性的影响.     

Palladium-Catalyzed Preparation of Dialkyl Allylphosphonates. A New Preparation of Diethyl 2-Oxoethylphosphonate

Palladium-catalyzed Michaelis-Arbuzov reaction of allyl acetates with trialkyl phosphites affords dialkyl allylphosphonates. Diethyl 2-oxoethylphosphonate is efficiently prepared by ozonization of diethyl allylphosphonate.     

Synthesis and evaluation of new phosphonated δ-lactam and glutarimide derivatives as angiotensin converting enzyme inhibitors

An efficient synthesis of new γ,δ-insaturated δ-lactam and glutarimide derivatives bearing a phosphonomethyl group from a common allylphosphonate precursor is described. Our approach is based on a two-step procedure involving the preparation of phosphonated-1,5-ketoester and −1,5-diester followed by an amidation–heterocyclization sequence. The first step proceeds via Michael's addition of ethyl acetoacetate and diethyl malonate on an allylphosphonate starting material. The second step consists of a base-promoted intramolecular amidation-cyclization sequence with primary amines, which accounts for the construction of δ-lactams and glutarimide skeletons. We performed the evaluation of angiotensin I-converting enzyme (ACE) inhibition using an in vitro enzyme assay on six new compounds. Five compounds showed potent ACE inhibitory activity, with IC₅₀ values ranging from 0.02 to 0.27 mg/ml. Compared with Captopril, used as a reference drug, two new glutarimide derivatives exhibited higher efficiency ACE inhibition activity.     

Synthese de Nouveaux Derives Phosphones a Chaine Perfluoree et Leurs Proprietes Adhesives Sur Acier

Ce mémoire décrit la synthèse de phosphonates comportant une chaîne perfluorée. Ces composés sont obtenus par la télomérisation d'allylphosphonates de dialkyle en présence d'un agent de transfert fluoré de type mercaptan. Ensuite, nous employons deux méthodes de déalkylation menant sélectivement soit au monoacide soit au diacide phosphonique. Tous ces produits comprenant une extrémité de chaîne phosphonée, sous forme acide ou ester, ont été caractérisés et leur adhésion respective sur des plaques d'acier est étudiée. Ces tests montrent que le monoacide phosphonique est un excellent promoteur d'adhésion et qu'il est aussi efficace que le diacide. This article describes the synthesis of phosphonic derivatives bearing a perfluorinated chain. These compounds have been synthetized by telomerization of dialkyl allylphosphonate with a fluorinated transfer agent type mercaptan. Then two methods of dealkylation leading selectively were used to mono or to diacid phosphonic moieties. All the products bearing phosphonic end-groups, more or less acidic, have been characterized and their own adhesion on steel plates is studied. These tests show that phosphonic monoacid is an excellent adhesion promoter on steel, as efficient as the diacid compound.     

Biosynthesis of Angular Furanocoumarins: Mechanism and Stereochemistry of the Oxidative Dealkylation of Columbianetin to Angelicin in Heracleum mantegazzianum (Apiaceae)

Deuterium-labelled 5-fluorocolumbianetin 13 was synthesized as a metabolic probe to examine the stereochemical course of the bioconversion of (+)-columbianetin ( 12 ) into the angular furocoumarin angelicin ( 5 ). In leaves of Heracleum mantegazzianum, oxidative dealkylation of the specifically deuterated fluorocolumbianetin 13 proceeded by syn-elimination of a D-atom, from C(9), and the vicinal 1-hydroxy-1-methylethyl substituent, yielding 5-fluoroangelicin ( 23 ). This matches the stereochemical course of the related reaction converting (+)-marmesin ( 10 ) into the linear furocoumarin psoralen ( 1 ). Key steps in the synthesis of 5-fluorocolumbianetin ( 13 ) were the copper-catalysed alkynylation/cyclization of 5-fluoro-8-iodoumbelliferone (15 ) followed by a transfer hydrogenation, which established the cis-orientation of the D-Atom and the 1-hydroxy-1-methylethyl substituent.     

Influence of Metallic Modification on Ethylbenzene Dealkylation over ZSM‐5 Zeolites

A series of metal‐modified HZSM‐5 catalysts were prepared by impregnation and were used for ethylbenzene dealkylation of the mixed C8 aromatics (ethylbenzene, m‐xylene and o‐xylene). The effects of different supported metals (Pt, Pd, Ni, Mo) on catalytic performance, including reaction conditions, were investigated. The physicochemical properties of catalysts were characterized by means of XRD, BET, TEM and NH₃‐TPD. Experimental results showed that metallic modification obviously increased the ethylbenzene conversion and reduced the coke deposition, greatly improving the catalyst stability. The distinction of ethylbenzene conversion depended on the interaction between hydrogenation reactivity and acidic cracking of bifunctional metal‐modified zeolites. Compared with Pt and Ni, Pd and Mo were easier to disperse into HZSM‐5 micropores during loading metals. The acidic density of different metal‐modified HZSM‐5 declined in the following order: HZSM‐5>Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. The activity of ethylene hydrogenation decreased with Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. In comparison, Pd/HZSM‐5 showed the best catalytic performance with both high activity and high selectivity, with less cracking loss of m‐xylene and o‐xylene. Moreover, the following reaction conditions were found to be preferable for ethylbenzene dealkylation over Pd/HZSM‐5: 340°C, 1.5 MPa H₂, WHSV 4 h^?1, H₂/C8 4 mol/mol.     

Diastereoselective synthesis of novel iminosugar-containing UDP-Galf mimics: potential inhibitors of UDP-Gal mutase and UDP-Galf transferases

Tetra-O-benzyl-D-glucofuranose was converted into uridine diphosphono-beta-Galf mimics based on an iminosugar skeleton linked to UMP by a 2-hydroxypropyl tether. The synthesis is based on the highly regio- and stereoselective cycloaddition of an original uridin-5'-yl allylphosphonate with a 1,4-dideoxy-1,4-iminogalactitol-derived cyclic nitrone, followed by the reductive elaboration of the cycloaddition product. The resulting iminogalactose-UMP conjugates are novel sugar nucleotide mimics which could be useful as inhibitors of UDP-Gal mutase and UDP-Galf transferases.     

Friedel-Crafts reactions in ionic liquids: the counter-ion effect on the dealkylation and acylation of methyl dehydroabietate

Ionic liquids with different counter-ion and alkyl substitutes were tested as solvents in the dealkylation and acylation of methyl dehydroabietate, a useful and inexpensive building block for the synthesis of higher diterpenes derivatives. Ionic liquids with halogen counter-ions are very active in both reactions with high rate constant and conversion, avoiding the use of the conventional solvents (benzene and carbon disulfide) in these reactions. In the dealkylation reaction, the change of counter-ion from halogens to tetrafluoroborate had a dramatic effect on the stereoselectivity, showing the importance of the counter-ion in the course of the reactions.     

Et3N-induced demethylation-annulation of 3-alkynyl-4-methoxy-2-pyridones and structurally related compounds in the synthesis of furan-fused heterocycles

Various 3-iodo-4-methoxypyridin-2-ones and related pyrone and coumarin derivatives have been demonstrated as readily available precursors of 2-substituted furan-fused heterocycles by means of in situ sequential Sonogashira-acetylide coupling, dealkylation, and regioselective furan annulation reactions. A Et3N-induced S(N)2 process has been established that accounts for the dealkylation process.     

Selective cleavage of the carbon-sulphur and carbon-oxygen bonds in methoxythioanisoles

Selective cleavage of thioether of ether functions in methoxythioanisoles in hexamethylphosphoramide (HMPA) with sodium gives methoxythiophenols by cleavage of the carbon-sulphur bond. Reactions with sodium isopropanethiolate give instead the thiomethoxyphenols by dealkylation of the methoxy function. When the methoxythioanisoles were treated first with sodium isopropanethiolate and then with sodium complete dealkylation was achieved with formation of mercaptophenols. The present methods have considerable advantages over existing procedures for the synthesis of methoxythiophenols, thiomethoxyphenols and mercaptophenols. The mechanistic implications of the reactions investigated are also discussed.     

Catalysis of the dealkylation of derivatives of 2,6-di-tert-butylphenol by heteropoly acids

Conclusions The tungsten heteropoly acids in acetic acid are the most active in the dealkylation of 4-alkyl-2,6-di-tert-butylphenols. The reaction is first order with respect to the substrate and with respect to the HPA, and water slows the reaction. It has been postulated that the dealkylation reaction is mediated mainly by the undissociated molecules of the HPA.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 752–756, April, 1987.     

Biosynthesis of Psoralen: Mechanism of a Cytochrome P450 Catalyzed Oxidative Bond Cleavage

In contrast to the stepwise oxidative dealkylation of steroids [Eq. (1)], (+)‐marmesin ( 1 ) is directly converted by the psoralen synthase (a cytochrome P450) into the phototoxic furanocoumarin psoralen ( 2 ) and acetone. The dealkylation proceeds as a syn elimination.     

First synthesis of 2-[alkylamino(diethoxyphosphoryl)methyl]acrylic ethyl esters

The ethyl α-bromomethyl-β-(diethoxyphosphoryl)acrylic acid ester 9 has been prepared by addition of bromine to allylphosphonate 7 then dehydrobromination with DBU in acetonitrile. Reaction of allylic bromide 9 with primary amines in a bimolecular S_N2′-type mecanism in methanol at low temperature, gives rise to the 2-[alkylamino(diethoxyphosphoryl)methyl]acrylic acid ethyl esters 6.     

Synthesis and utility of new amine/nucleobase addition products of allenylphosphonates

In the reaction of allenylphosphonates with amines/nucleobases, depending on the amine and the allenylphosphonate, either Z- or E-vinylphosphonate or allylphosphonate as a single isomer with a β-amino functionality was isolated. A simple route to phosphonates with a β-NH₂ group is developed by direct reaction with ammonia. In reactions with adenine, three different modes of reaction, with one of them involving an unusual cyclisation, are observed. The utility of (enamino)allyl phosphonate products thus obtained in the synthesis of (enamino)-1,3-butadienes via Horner-Wadsworth-Emmons (HWE) reaction is also demonstrated.     

Catalyst activity in alkylthiophene dealkylation

The transformations of 2-alkylthiophenes on various catalysts were studied. In the presence of oxide and sulfide catalysts, 2-methylthiophenes and 2-isopropylthiophenes underwent dealkylation to thiophene. The reaction was complicated by isomerization to 3-alkylthiophene and cracking. The dealkylation of 2-ethylthiophene occurred only in the presence of oxide catalysts. Side-chain dehydrogenation resulting in the formation of 2-vinylthiophene primarily occurred under the action of sulfide and some oxide catalysts. Acid catalysts (amorphous aluminosilicate and zeolites in the form of hydrogen) were the most active and selective in the dealkylation of 2-alkylthiophenes. It is believed that the dealkylation reaction of 2-alkylthiophenes on these catalysts occurs by means of a protolytic mechanism.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 97–103.Original Russian Text Copyright © 2005 by Mashkina, Chernov.     

Superelectrophilic amidine dications: dealkylation by triflate anion

Superelectrophiles: Formamides were designed that when treated with triflic anhydride would be transformed into superelectrophilic amidine dications. These dications were so electrophilic that they underwent in?situ dealkylation by the triflate anion (see scheme; Tf=trifluoromethanesulfonyl). DFT calculations were used to determine the mechanistic details of the dealkylation reaction.     

Synthesis of 2-substituted indoles via a palladium-catalyzed domino Heck reaction and dealkylation

A palladium-catalyzed domino Heck reaction and dealkylation for the preparation of 2-substituted indoles is described. This novel transformation is based on an intramolecular Heck reaction followed by dealkylation.     

Effect of heat treatment on the degradation of fiber anionites

The thermal transformations of anionites synthesized on the basis of a polyacrylonitrile fiber are studied. During the heat treatment of the weakly basic anionite FIBAN A-5, the cleavage of amino groups occurs via two routes. In the case of the strongly basic anionite FIBAN A-6, dealkylation and deamination occur during heating and the dealkylation of quaternary amino groups accompanied by formation of tertiary amino groups predominates. The thermal degradation of anionites proceeds much more intensely in an aqueous medium than in an atmosphere of inert gas owing to participation of water hydroxyl in the mentioned reactions.