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High Regioselectivity (high + regioselectivity)
Selected AbstractsChemInform Abstract: High Regioselectivity in Electrochemical ,-Methoxylation of N-Protected Cyclic Amines.CHEMINFORM, Issue 41 2008Samuel S. Libendi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: High Regioselectivity in Propylene Hydroformylation Using Rhodium-Bisphosphite Catalysts Is Due to Properties of the SRS Diastereomer.CHEMINFORM, Issue 7 2002John R. Briggs Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] 1,3-Dipolar cycloaddition reaction of 4,5-dihydro-1H -imidazole 3-oxides with alkynesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2006Sergey A. Popov 4,5-Dihydro-1H -imidazole 3-oxides bearing different substituents at positions 1 and 2 of the heterocycle were shown to react with a wide range of acceptor-substituted alkynes forming corrsponding cycloadducts - derivatives of 1,2,3,7a-tetrahydroimidazo[1,2- b]isoxazole. High regioselectivity of this process stipulated by conjugation of the nitrogen atom with the nitrone group was revealed. [source] Cover Picture: Bidentate Ligands by Self-Assembly through Hydrogen Bonding: A General Room Temperature/Ambient Pressure Regioselective Hydroformylation of Terminal Alkenes (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-13 2005Catal. Abstract The cover picture shows a typical industrial reaction, hydroformylation of terminal alkenes, made possible in a test tube with ambient pressure and room temperature with high regioselectivities. For more details, see the Communication by Wolfgang Seiche, Alexander Schuschkowski, and Bernhard Breit on pages 1488,1494. [source] Regio- and stereoselective synthesis of isoxazolidine derivatives by asymmetric 1,3-dipolar cycloaddition reaction of chiral nitrones with 1-propene-1,3-sultoneJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2008Hong-Kui Zhang Asymmetric 1,3-dipolar cycloadditions of chiral nitrones to 1-propene-1,3-sultone (1) were investigated. Chiral nitrones 6a-e reacted with sultone 1 in toluene at 90 °C for 24-36 h to give the corresponding isoxazolidines in moderate yields with high regioselectivities and stereoselectivities. The diastereoselectivity of this reaction varied with the choice of dipolarophile and the steric demands of nitrones. When sultone 1 was allowed to react chiral nitrone 6e, a much better diastereoselectivity of up to 5.1:1 was observed. [source] Organocatalyzed Highly Enantioselective Direct Aldol Reactions of Aldehydes with Hydroxyacetone and Fluoroacetone in Aqueous Media: The Use of Water To Control RegioselectivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Xiao-Hua Chen Abstract An organocatalyst prepared from (2R,3R)-diethyl 2-amino-3-hydroxysuccinate and L -proline exhibited high regio- and enantioselectivities for the direct aldol reactions of hydroxyacetone and fluoroacetone with aldehydes in aqueous media. It was found that water could be used to control the regioselectivity. The presence of 20,30 mol,% of the catalyst afforded the direct aldol reactions of a wide range of aldehydes with hydroxyacetone to give the otherwise disfavored products with excellent enantioselectivities, ranging from 91 to 99,%,ee, and high regioselectivities. Aldolizations of fluoroacetone with aldehydes mediated by 30 mol,% of the organocatalyst in aqueous media preferentially occurred at the methyl group, yielding products with high enantioselectivities (up to 91,%,ee); however, these additions took place dominantly at the fluoromethyl group in THF. Optically active 3,5-disubstituted tetrahydrofurans and (2S,4R)-dihydroxy-4-biphenylbutyric acid were prepared by starting from the aldol reaction of hydroxyacetone. Theoretical studies on the role of water in controlling the regioselectivity revealed that the hydrogen bonds formed between the amide oxygen of proline amide, the hydroxy of hydroxyacetone, and water are responsible for the regioselectivity by microsolvation with explicit one water molecule as a hydrogen-bond donor and/or an acceptor. [source] Peroxide/Potassium Iodide Redox Systems for in situ Oxyiodination of Organic Compounds under Liquid-Phase and Solvent-Free ConditionsHELVETICA CHIMICA ACTA, Issue 2 2010Gattu Venkateshwarlu Abstract Iodination of certain aromatic amines and phenols are triggered by the oxidation of KI by peroxy compounds such as tert -butyl hydroperoxide (tBuOOH) under liquid-phase and solvent-free conditions by grinding the reactants in a mortar with a pestle. The reactions afforded corresponding iodo derivatives in good yield with high regioselectivity (Table,1). [source] Synthesis of Some Novel Thioxanthenone-Fused Azacrown Ethers, and Their Use as New Catalysts in the Efficient, Mild, and Regioselective Conversion of Epoxides to , -Hydroxy Thiocyanates with Ammonium ThiocyanateHELVETICA CHIMICA ACTA, Issue 7 2007Hashem Sharghi Abstract The regioselective ring-opening reactions of some epoxides with ammonium thiocyanate in the presence of a series of new 9H -thioxanthen-9-one-fused azacrown ethers, i.e., 7,11 (Scheme,1), and also of dibenzo[18]crown-6 (12), Kryptofix®22 (13), and benzo[15]crown-5 (14) were studied (Tables 1 and 2). The epoxides were subjected to cleavage by NH4SCN in the presence of these catalysts under mild conditions in various aprotic solvents. Reagents and conditions were identified for the synthesis of individual , -hydroxy thiocyanates in high yield and with more than 90% regioselectivity. The results can be discussed in terms of a four-step mechanism (Scheme,2): 1) formation of a complex between catalyst and NH4SCN, 2) release of SCN, from the complex, 3) reaction of the released SCN, at the sterically less hindered site of the epoxide, and 4) regeneration of the catalyst. The major advantages of this method are the high regioselectivity, the simple regeneration of the catalyst, the reuse of it through several cycles without a decrease of activity, and the ease of workup of the reaction mixtures. [source] Highly Linear-Selective Hydroformylation of 1-Alkenes using Formaldehyde as a Syngas SubstituteADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Gouki Makado Abstract A highly linear-selective hydroformylation of 1-alkenes using formaldehyde without the direct use of syngas is described. One rhodium(I) complex catalyzes two processes in the overall hydroformylation of 1-alkenes using formaldehyde as the syngas substitute to give hydroformylated aldehydes with excellent regioselectivities. A high regioselectivity (linear/branched=up to 98/2) and chemical yield (up to 95%) can be achieved by the simultaneous use of two types of phosphanes as ligands. [source] Highly Efficient Halogenation of Organic Compounds with Halides Catalyzed by Cerium(III) Chloride Heptahydrate Using Hydrogen Peroxide as the Terminal Oxidant in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Habib Firouzabadi Abstract In this article a new environmentally friendly catalytic method is described for the efficient monoiodination and bromination of arenes and also iodoetherification and iodolactonization of olefins using hydrogen peroxide as the terminal oxidant. The method is based on using sodium iodide or sodium bromide, hydrogen peroxide (35%) and cerium(III) chloride as an effective catalyst in water at room temperature or under reflux conditions. By this protocol, iodination of anilines proceeded with high regioselectivity at the para position with the formation of small amounts of the ortho isomers. However, bromination of anilines proceeded with absolute regioselectivity to give the para isomers as the sole products in high yields. Iodinations and brominations of m -xylene, toluene, chloro- and bromobenzenes were proceeded with excellent regioselectivity to produce the para isomers as the sole products. Benzene was also halogenated by this catalytic system to give the monohalogenated benzene in good yields. Iodoetherification and iodolactonization of olefins also proceeded easily in high yields at room temperature. However, the bromination of olefins by this protocol failed and the starting materials were detected intact. [source] Highly Regioselective and Rapid Hydroformylation of Alkyl Acrylates Catalyzed by a Rhodium Complex with a Tetraphosphorus LigandADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Shichao Yu Abstract Alkyl acrylates have been hydroformylated to the linear aldehydes with high regioselectivity (linear/branch>99/1) and extraordinarily high average turnover frequencies (up to 5400,h,1) by using a rhodium complex with a tetraphosphorus ligand. This protocol is in sharp contrast to the most of other processes that favor production of the branched aldehyde (typically>95% branched for most Rh-catalyzed reaction systems). The high turnover number achieved by this new catalytic system is also remarkable considering the less reactive character of alkyl acrylates to the hydroformylation reaction conditions. [source] Novel [Ruthenium(substituted-tetramethylcyclopentadiene) (2-quinolinecarboxylato)(allyl)] Hexafluorophosphate Complexes as Efficient Catalysts for Highly Regioselective Nucleophilic Substitution of Aliphatic Allylic SubstratesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2008Hui-Jun Zhang Abstract Stable [ruthenium(R-substituted-tetramethylcyclopentadiene)(2-quinolinecarboxylato)(1-R,-substituted-allyl) hexafluorophosphate (R=Me, R,=H, Me, n- Pr, Ph; R=t- Bu, R,=Me) and [ruthenium(pentamethylcyclopentadiene)(2-quinolinecarboxylato)(1- n -propylallyl)] tetrafluoroborate (4,a), as allylruthenium(IV) complexes, have been synthesized in one step, starting from [ruthenium(R-substituted-tetramethylcyclopentadiene)tris(acetonitrile) hexafluorophosphate or tetrafluoroborate complexes, quinaldic acid, and allylic alcohols. Single stereoisomers are obtained and the X-ray single crystal structure determinations of 3b (R=t- Bu, R,=Me) and 4,a allow one to specify the preferred arrangement. Complexes 3a (R=R,=Me) and 3b are involved as precatalysts favoring the formation of branched products in regioselective nucleophilic allylic substitution reactions, starting from ethyl 2- (E) -hexen-1-yl carbonate and chlorohexene as unsymmetrical aliphatic allylic substrates. Phenols, dimethyl malonate, and primary (aniline) and secondary (pyrrolidine, piperidine) amines have been used as nucleophiles under mild basic conditions. For the first time, the regioselectivity in favor of the branched product obtained from purely aliphatic allylic substrates is close to the high regioselectivity previously reached starting from cinnamyl-type substrates in the presence of ruthenium catalysts. [source] A Modular Approach to ,-Arylated Carbonyl Compounds via Indium Tris(bistriflylamide)-Catalyzed Regioselective Addition of ,-Ketoesters to 1,3-DiynesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-13 2005Masaharu Nakamura Abstract A modular synthesis of ,-arylated carbonyl compounds has been achieved by the combination of an indium-catalyzed regioselective addition of ,-keto esters to conjugated diynes and a palladium-catalyzed benzannulation reaction. Indium tris(bistriflylamide), In(NTf2)3, was found to be an efficient catalyst for the first addition reaction of ,-keto esters to diynes. The reaction proceeds with perfect regioselectivity to give conjugated enynes in high yield. The second palladium-catalyzed benzannulation proceeds in high to excellent yield and with high regioselectivity for a variety of diynes. This two-step ,-arylation of carbonyl compounds thus proceeds in a catalytic manner without loss of elements in the starting materials. The reaction may be performed in a single pot without isolation of the product of the first step. [source] Synthesis and physicochemical properties of new 1N o -(m - and p -) bromobenzyl substituted derivatives of 5-(aminodialkyl)methylcytosineJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2007Dorota Prukala Simple alkylation of 5-(aminodialkyl)methylcytosine a-d gives twelve new, potentially biologically active 1N o -(m - or p -) bromobenzyl derivatives of 5-substituted cytosine 1-12 with high regioselectivity. The structures of all compounds have been confirmed by elemental analysis, IR, 1H NMR and 13C NMR spectroscopic measurements. [source] Reaction of 4,5,6-triaminopyrimidine and 2,4,5,6-tetraaminopyrimidine with 3-dimethylaminopropiophenones.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 20003-dihydropyrimido[, 4]diazepines, 5- b][, Synthesis of new 4-aryl- Several new 6-amino- and 6,8-diamino-4-aryl-2,3-dihydropyrimido[4,5- b][1,4]diazepines were obtained from the reaction of 4,5,6-triaminopyrimidine 1a and 2,4,5,6-tetraaminopyrimidine 1b with one equivalent of 3-dimethylaminopropiophenones 2 in absolute ethanol. Structure analysis of 6-amino- and 6,8-diamino-4-aryl-2,3-dihydropyrimido[4,5- b][1,4]diazepines 3a-i, determined by detailed nmr measurements, reveals a high regioselectivity of this reaction. [source] Controlled cationic polymerization of cyclopentadiene with B(C6F5)3 as a coinitiator in the presence of waterJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008Sergei V. Kostjuk Abstract The controlled cationic polymerization of cyclopentadiene (CPD) at 20 °C using 1-(4-methoxyphenyl)ethanol (1)/B(C6F5)3 initiating system in the presence of fairly large amount of water is reported. The number,average molecular weights of the obtained polymers increased in direct proportion to monomer conversion in agreement with calculated values and were inversely proportional to initiator concentration, while the molecular weight distribution slightly broadened during the polymerization (Mw/Mn , 1.15,1.60). 1H NMR analyses confirmed that the polymerization proceeds via reversible activation of the COH bond derived from the initiator to generate the growing cationic species, although some loss of hydroxyl functionality happened in the course of the polymerization. It was also shown that the enchainment in cationic polymerization of CPD was affected by the nature of the solvent(s): for instance, polymers with high regioselectivity ([1,4] up to 70%) were obtained in acetonitrile, whereas lower values (around 60%) were found in CH2Cl2/CH3CN mixtures. Aqueous suspension polymerization of CPD using the same initiating system was successfully performed and allowed to synthesize primarily hydroxyl-terminated oligomers (Fn = 0.8,0.9) with Mn , 1000 g mol,1 and broad MWD (Mw/Mn , 2.2). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4734,4747, 2008 [source] An Inverse Substrate Orientation for the Regioselective Acylation of 3,,5,-Diaminonucleosides Catalyzed by Candida antarctica lipase B?CHEMBIOCHEM, Issue 8 2005Iván Lavandera Dr. Abstract Candida antarctica lipase B (CAL-B) catalyzes the regioselective acylation of natural thymidine with oxime esters and also the regioselective acylation of an analogue, 3,,5,-diamino-3,,5,-dideoxythymidine with nonactivated esters. In both cases, acylation favors the less hindered 5,-position over the 3,-position by upto 80-fold. Computer modeling of phosphonate transition-state analogues for the acylation of thymidine suggests that CAL-B favors acylation of the 5,-position because this orientation allows the thymine ring to bind in a hydrophobic pocket and forms stronger key hydrogen bonds than acylation of the 3,-position. On the other hand, computer modeling of phosphonamidate analogues of the transition states for acylation of either the 3,- or 5,-amino groups in 3,,5,-diamino-3,,5,-dideoxythymidine shows similar orientations and hydrogen bonds and, thus, does not explain the high regioselectivity. However, computer modeling of inverse structures, in which the acyl chain binds in the nucleophile pocket and vice versa, does rationalize the observed regioselectivity. The inverse structures fit the 5,-, but not the 3,-intermediate thymine ring, into the hydrophobic pocket, and form a weak new hydrogen bond between the O-2 carbonyl atom of the thymine and the nucleophile amine only for the 5,-intermediate. A water molecule might transfer a proton from the ammonium group to the active-site histidine. As a test of this inverse orientation, we compared the acylation of thymidine and 3,,5,-diamino-3,,5,-dideoxythymidine with butyryl acyl donors and with isosteric methoxyacetyl acyl donors. Both acyl donors reacted at equal rates with thymidine, but the methoxyacetyl acyl donor reacted four times faster than the butyryl acyl donor with 3,,5,-diamino-3,,5,-dideoxythymidine. This faster rate is consistent with an inverse orientation for 3,,5,-diamino-3,,5,-dideoxythymidine, in which the ether oxygen atom of the methoxyacetyl group can form a similar hydrogen bond to the nucleophilic amine. This combination of modeling and experiments suggests that such lipase-catalyzed reactions of apparently close substrate analogues like alcohols and amines might follow different pathways. [source] Synthesis and Electrochemical Studies of Bingel,Hirsch Derivatives of M3N@Ih -C80 (M=Sc, Lu)CHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2010Julio Abstract Bingel,Hirsch derivatives of the trimetallic nitride template endohedral metallofullerenes (TNT-EMFs) Sc3N@Ih -C80 and Lu3N@Ih -C80 were prepared by reacting these compounds with 2-bromodiethyl malonate, 2-bromo-1,3-dipyrrolidin-1-ylpropane-1,3-dionate bromide, and 9-bromo fluorene. The mono-adducts were isolated and their 1H,NMR spectra showed that the addition occurred with high regioselectivity at the [6,6] bonds of the Ih -C80 fullerene cage. Electrochemical analysis showed that the reductive electrochemistry behavior of these derivatives is irreversible at a scan rate of 100,mV,s,1, which is comparable to the behavior of the pristine fullerene species. The first reduction potential of each derivative is either cathodically or anodically shifted by a different value, depending on the attached addend. Bis-adducts containing EtOOC-C-COOEt and HC-COOEt addends were isolated by HPLC and in the case of Sc3N@Ih -C80 the first reduction potential exhibits a larger shift towards negative potentials when compared to the mono-adduct. This observation is important for designing acceptor materials for the construction of bulk heterojunction (BHJ) organic solar cells, since the polyfunctionalization not only increases the solubility of the fullerene species but also offers a promising approach for bringing the LUMO energy levels closer for the donor and the acceptor materials. [source] Palladium Pincer Complex Catalyzed Cross-Coupling of Vinyl Epoxides and Aziridines with Organoboronic AcidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2005Johan Kjellgren Abstract Palladium-catalyzed cross-coupling of vinyl epoxides and aziridines with organoboronic acids was performed by using 0.5,2.5 mol,% pincer-complex catalyst. The reactions proceed under mild conditions affording allyl alcohols and amines with high regioselectivity and in good to excellent yields. Under the applied reaction conditions aromatic chloro-, bromo- and iodo substituents are tolerated. Our results indicate that the mechanism of the pincer complex catalyzed and the corresponding palladium(0) catalyzed process is substantially different. It was concluded that the transformations proceed via transmetalation of the organoboronic acids to the pincer-complex catalyst followed by an SN2,-type opening of the vinyl epoxide or aziridine substrate. In this process the palladium atom is kept in oxidation state +2 under the entire catalytic process, and therefore oxidative side reactions can be avoided. [source] | ||||||||||||||||||||||