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Reaction Sequence (reaction + sequence)
Kinds of Reaction Sequence Selected AbstractsStereodefined Access to 3-Deoxy Sugars Through a Tandem Baylis,Hillman and Lewis Acid Catalyzed Reaction SequenceEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2010Palakodety Radha Krishna Abstract An innovative synthetic protocol is reported for the ready access to 3-deoxy sugars in both D and L forms as exclusive products (des >95,%) in high yields through a stereodefined Lewis acid catalyzed reaction sequence of the sugar-derived Baylis,Hillman adducts. [source] One-Pot Three-Step Synthesis of Naphtho[2,3- a]carbazole- 5,13-diones using a Tandem Radical Alkylation,Cyclization, Aromatization Reaction SequenceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010Chunyong Ding Abstract A three-step, one-pot tandem reaction including radical nucleophilic alkylation/cyclization/aromatization was developed using 0.3 equivalents of silver(I) acetate (AgOAc) as the catalyst and 2 equivalents of ammonium persulfate [(NH4)2S2O8] as the oxidant. This strategy is highly efficient for the assembly of pentacyclic complex carbazoles from aryl-fused bromobenzoquinones and indol-3-ylpropanoic acid acids in 52,72% overall yields (three steps). This new approach provides a significant improvement over the previously reported methods and would greatly facilitate analog library construction of pentacyclic complex carbazoles and benefit further biological evaluation of these compounds. [source] Synthesis of Pyridines and Pyrazines Using an Intramolecular Hydroamination-Based Reaction Sequence,ANGEWANDTE CHEMIE, Issue 44 2009Toni Rizk Richtig organisiert! Eine Vielzahl an Pyridinen und Pyrazinen lässt sich mit einer Sequenz aus intramolekularer Hydroaminierung, Isomerisierung und Aromatisierung effizient aus einfachen acyclischen Vorstufen herstellen (siehe Schema). p -Toluolsulfonsäure (2,Mol-%) katalysiert diesen neuartigen Ringschluss, bei dem die Oximeinheit die redoxneutrale Aromatisierung ermöglicht. [source] ChemInform Abstract: Synthesis of Pyridines and Pyrazines Using an Intramolecular Hydroamination-Based Reaction Sequence.CHEMINFORM, Issue 7 2010Toni Rizk 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] ChemInform Abstract: A Sakurai,Prins,Ritter Reaction Sequence for the Diastereoselective Synthesis of 4-Amidotetrahydropyrans Catalyzed by Bismuth Triflate.CHEMINFORM, Issue 3 2009Gowravaram Sabitha 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: Orthoplatinated Triarylphosphite as a Highly Efficient Catalyst for Addition Reactions of Arylboronic Acids with Aldehydes: Low Catalyst Loading Catalysis and a New Tandem Reaction Sequence.CHEMINFORM, Issue 45 2008Yuan-Xi Liao 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: Directed Diastereoselectivity in the Asymmetric Claisen/Metathesis Reaction Sequence.CHEMINFORM, Issue 41 2008Nicolas P. Probst 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] A Three-Component Approach to Isoquinoline Derivatives by Cycloaddition/Heck Reaction Sequence.CHEMINFORM, Issue 39 2007Masato Oikawa 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, please click on HTML or PDF. [source] A Two-Step Reaction Sequence for the Synthesis of Tetrahydronaphthalenes.CHEMINFORM, Issue 22 2005Gerhard Hilt Abstract For Abstract see ChemInform Abstract in Full Text. [source] Alternation of Chemoselective Control in Stille,Heck and Heck,Stille Reaction SequencesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Kye-Simeon Masters The communication by Kye-Simeon Masters and Bernard L. Flynn in Issue 4, 2009, pp. 530,536 (DOI: 10.1002/adsc.200800678), should have appeared in this issue dedicated to Professor Armin de Meijere. It was published in Issue 4, 2009, by mistake. On the title page, below the received and publication dates, the following dedication should appear: "Dedicated to Professor Armin de Meijere on the occasion of his 70th birthday." The editorial office apologizes for this mistake. [source] Alternation of Chemoselective Control in Stille,Heck and Heck,Stille Reaction SequencesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Kye-Simeon Masters Abstract Sequential and one-pot Stille,Heck and Heck,Stille reaction processes have been invoked to give divergent access to polycyclic ring systems. Both reaction conditions and substrate structure are important in determining the nature of the reaction products formed. The Heck,Stille reactions have involved a reversal of the usual Heck regioselectivity and both cine- and ipso- substitutions have been observed in the Stille reaction. [source] Effect of Controlling Parameters on the Reaction Sequences of Formation of Nitrogen-Containing Magnesium Aluminate Spinel from MgO, Al2O3, and AlNJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2004Siddhartha Bandyopadhyay The reaction sequences of the formation of nitrogen-containing magnesium aluminate spinel from MgO, Al2O3, and AlN were investigated as a function of temperature through dilatometric study and as a function of time through isothermal heat treatments. The natures of reactions are described through the appearance of phases in conjunction with densification behavior and the change in lattice parameter of the spinel phase. Although the dilatometric study provides the detail insights of the formation sequence, the isothermal runs reveal new information about the differential rate of reactivity of the reacting species that suggested a tentative controlling mechanism. Through the initial formation of magnesium aluminate, oxygen-rich solid solution (MgAlON) forms, which ultimately reacts with the rest of AlN to reach its nominal composition. Nitrogen diffusion through MgAlON lattice seems to be rate controlling. [source] ChemInform Abstract: Enantioselective Synthesis of 2-Methyl-1,2-syn- and 2-Methyl-1,2-anti-3-butenediols via Allene Hydroboration,Aldehyde Allylboration Reaction Sequences.CHEMINFORM, Issue 8 2010Ming Chen 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] Gas-phase ion chemistry in the ternary silane,propyne,phosphine systemJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2004Lorenza Operti Abstract The gas-phase ion chemistry of propyne,phosphine and silane,propyne,phosphine mixtures was studied by ion trap mass spectrometry. For the binary mixture, the effect of different partial pressures of the reagents on the yield of C and P-containing ions was evaluated. Reaction sequences and rate constants were determined and reaction efficiencies were calculated from comparison of experimental and collisional rate constants. In the ternary silane,propyne,phosphine systems, the reaction pathways leading to formation of SimCnPpHq+ ions were determined and the rate constants of the most important steps were measured. For some ion species, selected by double isolation procedures (MS/MS), the low ion abundances prevented determination of the reaction rate constants. Si, C and P-containing ions are mainly produced in reactions of SimPpHq+ ions with propyne, while the reactivity of the SimCnHq+ ions towards PH3 and of the CnPpHq+ ions towards SiH4 is very low. The formation of hydrogenated SiCP ions is interesting for their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained in a single step, by deposition from properly activated silane,propyne,phosphine mixtures. Copyright © 2004 John Wiley & Sons, Ltd. [source] quart -Feproline: Synthesis of a Very Rigid [3]Ferrocenophane-Derived Artificial Amino AcidEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2008Ludger Tebben Abstract Starting from the ,-(dimethylamino)[3]ferrocenophane derivative 1, a short reaction sequence was developed to form a doubly anellated dihydropyrrole derivative 6 containing the ferrocenophane framework. Intermediate 6 was used for the synthesis of the (R,S,pS)-enantiomer of the rigid artificial amino acid "quart -Feproline". (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Electron-Sponge Behavior, Reactivity and Electronic Structures of Cobalt-Centered Cubic Co9Te6(CO)8 ClustersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2008Mustapha Bencharif Abstract Extended investigations of the reaction sequence [Cp,2Nb(Te2)H]/CH3Li/[Co2(CO)8] (Cp, = tBuC5H4) led to the identification of Lin[3] {3 = [Co9Te6(CO)8]; n = 1, 2} salts through their transformation with [PPN]Cl into [PPN]n[3] (PPN = Ph3PNPPh3). These compounds form in the solid state columnar ([PPN][3]) or undulated 2D ([PPN]2[3]) supramolecular networks. Electrochemical studies of [Cp*2Nb(CO)2][3] (Cp* = C5Me5) or [Na(THF)6][3] revealed the presence of the redox couples [3],/[3]2,/[3]3,/[3]4,/[3]5, regardless of the nature of the cation, whereas in the anodic part oxidative degradation of the cluster takes place. This behavior is in agreement with the observation that [3], containing salts form with PPh3AuCl or dppe decomposition products like [(PPh3)2Au][CoCl3PPh3] or [Co(CO)2dppe]2(,-Te). A neutral cluster comprising the Co@Co8(,4 -Te)6 core formed in the reaction of [Cp*2Nb(CO)2][Co11Te7(CO)10] with PPh3AuCl, which gave [Co9Te6(CO)4(PPh3)4] (4) after oxidative cluster degradation and CO substitution. 4 was characterized by X-ray crystallography. DFT calculations carried out on all members of the [3]n (n = +1 to ,5) family and on related species indicate that there is no significant Jahn,Teller distortion (and therefore no connectivity change) for any of the considered electron counts. Magnetic investigations on [PPN][3] show that the ground state of [3], is a spin triplet with spins interacting antiferromagnetically in a 1D space.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] The First Heterohexametallic Transition-Metal ComplexEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2007Rico Packheiser Abstract The synthesis and characterisation of a first heteromultimetallic transition metal complex with six different metal atoms (Fe, Ru, Re, Au, Cu and Ti), connected through carbon-rich bridging units, are reported. Complex {1-[(,2 -dppf)(,5 -C5H5)RuC,C]-3-[(bipy*)(CO)3ReC,C]-5-[PPh2AuC,C-bipy({[Ti](,-,,,-C,CSiMe3)2}Cu)]C6H3}PF6 is accessible in a consecutive reaction sequence by applying building blocks from a ligand and coordination complex library. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Permanganate Oxidation Revisited: Synthesis of 3-Deoxy-2-uloses via Indium-Mediated Chain Elongation of CarbohydratesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Christoph Schmölzer Abstract Application of the Barbier-type indium-mediated allylation method to suitable substrates offers access to carbohydrates bearing a terminal olefin moiety. The C,C bond forming reaction generates a defined stereochemistry of the new chiral center and tolerates a wide variety of starting aldehydes thus allowing modifications in the carbohydrate backbone. Further transformations of the alkene moiety via an environmentally benign and subtle controlled protocol using potassium permanganate gives rise to the structural motif of 3-deoxy-2-uloses in good yields. The final part of the reaction sequence focuses on the deprotection of the acetyl groups essential for the success of the oxidation step. The acidic and labile 3-deoxy position of the target molecule is prone to elimination applying standard deacetylation conditions and therefore demands derivatisation of the molecule. The introduction of a thioketal moiety using microwave conditions shows promising results and subsequent standard transformations are applicable leading to the desired products. [source] Stereodefined Access to 3-Deoxy Sugars Through a Tandem Baylis,Hillman and Lewis Acid Catalyzed Reaction SequenceEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2010Palakodety Radha Krishna Abstract An innovative synthetic protocol is reported for the ready access to 3-deoxy sugars in both D and L forms as exclusive products (des >95,%) in high yields through a stereodefined Lewis acid catalyzed reaction sequence of the sugar-derived Baylis,Hillman adducts. [source] Cascade Annulation Reactions To Access the Structural Cores of Stereochemically Unusual Strychnos AlkaloidsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2009Ricardo Delgado Abstract A new cascade annulation reaction has been developed to access the core structures of a novel family of strychnos alkaloids with a unique stereochemical arrangement. The new annulation cascade is facilitated by the development of a robust reaction sequence to access extremely sensitive N -acyliminium ions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] The Mechanism of the Stetter Reaction , A DFT StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2008Kirsty J. Hawkes Abstract On the basis of Breslow's mechanism for benzoin condensation, a model asymmetric Stetter reaction has been investigated using DFT methods. In contrast to the concerted benzoin condensation, after formation of the Breslow intermediate the Stetter reaction is found to be a two-step process in which the rate-determining C,C coupling of the Breslow intermediate and the Michael acceptor precedes final proton transfer. In addition, the enolamine is found to play a significant role in the stereochemistry of the product, with the energy difference between stereoisomers of this intermediate reflected throughout the remainder of the reaction sequence. Consequently, electronic and steric control of the stereochemistry of this intermediate should directly enhance the ee values of the product. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Superacid-Catalyzed Dimerization/Cyclization of Isopropenyl-PAHs , Novel Pathways to PAH Dimers, Phenalenes and Their Stable CarbocationsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2008Cédric Brulé Abstract The isopropenyl derivatives of representative classes of polycyclic aromatic hydrocarbons (PAHs) having four and five fused-ring systems, namely pyrene, chrysene, benzo[c]phenanthrene (BcPh), dibenzo[a,c]anthracene (benzo[f]tetraphene) and perylene, were synthesized by Wittig olefination from the corresponding acetyl-PAHs. Under the influence of triflic acid (TfOH), the isopropenyl derivatives were converted to novel PAH dimers and/or phenalenes in a simple one-pot procedure. A plausible mechanism for this process has been outlined, and the synthetic scope of this chemistry has been explored. Structural features in the PAH dimers were examined by DFT. As representative initial and final carbocation intermediates in the reaction sequence, stable carbocations derived from 3-isopropenylperylene and from 4,6,6-trimethyl-6H -dibenzo[a,kl]anthracene were generated and studied directly by NMR spectroscopy. The NMR characteristics and charge delocalization modes in the resulting benzylic carbocations are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Development of Pharmaceutical Drugs, Drug Intermediates and Ingredients by Using Direct Organo-Click ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2008Dhevalapally B. Ramachary Abstract Here we report on our studies of the use of combinations of amino acids, amines, K2CO3 or Cs2CO3 and CuSO4/Cu for catalysing green cascade reactions. We aimed to prepare the highly reactive and substituted olefin species 7 and 8, under very mild and environmentally friendly conditions, thus giving the hydrogenated products 10 and 12 through the action of Hantzsch ester (4) by self-catalysis through decreasing the HOMO,LUMO energy gaps between olefins 7/8 and Hantzsch ester (4) through biomimetic reductions. Highly useful compounds 10 to 14 were assembled from simple substrates such as aldehydes 1, ketones 2, CH acids 3, Hantzsch ester (4) and alkyl halides 5 by diversity-oriented green synthesis involving cascade olefination/hydrogenation (O/H), olefination/hydrogenation/alkylation (O/H/A) and hydrogenation/olefination/hydrogenation (H/O/H) reaction sequences in one-pot fashion with stereospecific organo- and organo-/metal-carbonate catalysis. Highly functionalized diverse compounds such as 10 to 14 are biologically active products and have found wide applications as pharmaceutical drugs, drug intermediates and drug ingredients. For the first time in organocatalysis, we report the O/H/A/TE reaction to furnish high yields of transesterification products 11 by simply mixing the reactants under proline/K2CO3 catalysis conditions. Additionally, a novel organocatalytic H/O/H reaction sequence for the synthesis of alkyl-substituted aromatics has been developed. Furthermore, for the first time we have developed organocatalysed cascade olefination/hydrogenation/hydrolysis (O/H/H) reactions to furnish highly useful materials such as 2-oxochroman-3-carboxylic acid (14kc) and 2-amino-4H -chromene-3-carbonitrile (14kj) in good yields. Experimentally simple and environmentally friendly organocatalytic two-carbon homologation through cascade O/H/H reactions of aldehydes 1, Meldrum's acid (3c), Hantzsch ester (4) and acetic acid/triethylamine in ethanol has been demonstrated. Additionally, we have developed a green synthesis of the highly substituted 1,2,3-triazole 17 from simple substrates through a two-step combination of olefination/hydrogenation/alkylation and Huisgen cycloaddition reaction sequences under stereospecific organocopper catalysis conditions. In this paper we have found strong support for our hypothesis that, "decreasing the HOMO,LUMO energy gap between olefins 7/8 and Hantzsch ester (4) will drive the biomimetic hydrogenation reaction by self-catalysis". This self-catalysis was further confirmed with many varieties of examples.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Fluorous "Racemic" Mixture Synthesis: Simultaneous Strategy for Demixing and Enantioseparation of Racemic Fluorous-Tagged ProductsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2007Takayuki Tonoi Abstract Reported herein is the concept of fluorous "racemic" mixture synthesis (FRMS), which is applied to two types of proof-of-concept experiments. Mixtures of racemic O -benzoylmandelate derivatives and prochiral crotonamide derivatives, respectively, bearing different lengths of fluorous-cleavable tags are taken through a segmented reaction sequence to provide their enantiomers, as well as their individual derivatives, by virtue of chiral ,-cyclodextrin columns. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis of New Tetrazole-Substituted Pyroaminoadipic and Pipecolic Acid DerivativesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2005Fatimazohra Lenda Abstract Racemic 5-aryl- and 5-(arylmethyl)tetrazolyl-substituted pyroaminoadipic and pipecolic acid derivatives were diastereoselectively synthesized from dimethyl meso -2,5-dibromoadipate (1) in good yields under mild reaction conditions. The key step of this reaction sequence is the selective N2 -alkylation of 5-substituted tetrazoles with 1. The reactive 2-bromo-5-tetrazolyladipate derivatives 2a,g were generated and treated with sodium azide, followed by Pd/C-catalyzed hydrogenation, to provide lactams 4a,g. The chemoselective reduction of the amide carbonyl group of 4a,g with BH3, followed by acid hydrolysis, provided 5-tetrazolylpipecolic acids in racemic form. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Efficient Synthesis of Structurally Diverse Diazabicycloalkanes: Scaffolds for Modular Dipeptide Mimetics with Tunable Backbone ConformationsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2004Wolfgang Maison Abstract A stereoselective synthesis of new dipeptide mimetics based on a diazabicycloalkane scaffold is reported. The route starts from enantiomerically pure azabicycloalkenes 1 that are bis(hydroxylated) and coupled N -terminally to a second amino acid. The key step of the reaction sequence is an oxidative cleavage of the resulting dipeptides 5 to give highly functionalised diazabicycloalkanes 6, which can be easily converted into a number of dipeptide mimetics with defined and variable stereochemistry and a number of different amino acid side chains. The backbone dihedral angles within these dipeptide mimetics can be tuned by varying the stereochemistry and the ring sizes of the diazabicycloalkane scaffold. The syntheses of conformationally constrained dipeptide analogues in four to five steps are presented. With the syntheses of dipeptide mimetics 19a,c, suitable linker moieties for conjugation of diazabicycloalkanes to other functional molecules like markers or solid phases are introduced, making these compounds modular dipeptide mimetics that might find applications as modular ligands or as solid-phase-attached scaffolds in combinatorial chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Polyphase evolution and reaction sequence of compositional domains in metabasalt: a model based on local chemical equilibrium and metamorphic differentiationGEOLOGICAL JOURNAL, Issue 3-4 2000T. M. Toóth Abstract Eclogitic garnet amphibolite samples from the Southern Steep Belt of the Central Alps show evidence of several stages of metamorphic evolution and exhumation. A method for unravelling this evolution is presented and applied to these samples. It involves a combination of detailed petrographic analysis and microchemical characterization with quantitative models of the thermodynamically stable phase relations for specific compositional domains of each sample. Preserved mineral relics and textural evidence are compared to model predictions to identify the important irreversible reactions. The interpretation of the exhumation history is thus based on the consistency of a wide spectrum of observations with predicted phase diagrams, leading to robust reconstruction of a pressure,temperature (P,T) path even where the mineralogical relics in samples are insufficient, due to retrogression, to warrant application of multi-equilibrium thermobarometric techniques. The formation of compositionally different domains in the metabasalt samples studied is attributed to prograde growth of porphyroblasts (e.g. garnet, plagioclase, zoisite) in the matrix, implying substantial metamorphic differentiation at the scale of a few millimetres. Chemical interaction among different domains during the subsequent P,T evolution is shown to have been very limited. This led to different reaction sequences during exhumation, in which relics preserved in different domains reflect a range of continually changing P,T conditions. For samples from a single outcrop, we deduce a Barrovian prograde path to eclogite facies (23,±,3,kbar, 750,±,50°C), followed by (rapid) decompression to 8,±,1,kbar and 675,±,25°C, and a final heating phase at similar pressures reaching 750,±,40°C. This evolution is attributed to the Alpine cycle involving subduction,collision and slab breakoff,extrusion of tectonic fragments that make up the Southern Steep Belt of the Central Alps. Copyright © 2000 John Wiley & Sons, Ltd. [source] Benzo[a]heptalenes from Heptaleno[1,2- c]furans.HELVETICA CHIMICA ACTA, Issue 4 2007Abstract It is shown in this ,Part 2' that heptaleno[1,2- c]furans 1 react thermally in a Diels,Alder -type [4+2] cycloaddition at the furan ring with vinylene carbonate (VC), phenylsulfonylallene (PSA), , -(acetyloxy)acrylonitrile (AAN), and (1Z)-1,2-bis(phenylsulfonyl)ethene (ZSE) to yield the corresponding 1,4-epoxybenzo[d]heptalenes (cf. Schemes,1, 5, 6, and 8). The thermal reaction of 1a and 1b with VC at 130° and 150°, respectively, leads mainly to the 2,3- endo -cyclocarbonates 2,3- endo - 2a and - 2b and in minor amounts to the 2,3- exo -cyclocarbonates 2,3- exo - 2a and - 2b. In some cases, the (P*)- and (M*)-configured epimers were isolated and characterized (Scheme,1). Base-catalyzed cleavage of 2,3- endo - 2 gave the corresponding 2,3-diols 3, which were further transformed via reductive cleavage of their dimesylates 4 into the benzo[a]heptalenes 5a and 5b, respectively (Scheme,2). In another reaction sequence, the 2,3-diols 3 were converted into their cyclic carbonothioates 6, which on treatment with (EtO)3P gave the deoxygenated 1,4-dihydro-1,4-epoxybenzo[d]heptalenes 7. These were rearranged by acid catalysis into the benzo[a]heptalen-4-ols 8a and 8b, respectively (Scheme,2). Cyclocarbonate 2,3- endo - 2b reacted with lithium diisopropylamide (LDA) at ,70° under regioselective ring opening to the 3-hydroxy-substituted benzo[d]heptalen-2-yl carbamate 2,3- endo - 9b (Scheme,3). The latter was O -methylated to 2,3- endo -(P*)- 10b. The further way, to get finally the benzo[a]heptalene 13b with MeO groups in 1,2,3-position, could not be realized due to the fact that we found no way to cleave the carbamate group of 2,3- endo -(P*)- 10b without touching its 1,4-epoxy bridge (Scheme,3). The reaction of 1a with PSA in toluene at 120° was successful, in a way that we found regioisomeric as well as epimeric cycloadducts (Scheme,5). Unfortunately, the attempts to rearrange the products under strong-base catalysis as it had been shown successfully with other furan,PSA adducts were unsuccessful (Scheme,4). The thermal cycloaddition reaction of 1a and 1b with AAN yielded again regioisomeric and epimeric adducts, which could easily be transformed into the corresponding 2- and 3-oxo products (Scheme,6). Only the latter ones could be rearranged with Ac2O/H2SO4 into the corresponding benzo[a]heptalene-3,4-diol diacetates 20a and 20b, respectively, or with trimethylsilyl trifluoromethanesulfonate (TfOSiMe3/Et3N), followed by treatment with NH4Cl/H2O, into the corresponding benzo[a]heptalen-3,4-diols 21a and 21b (Scheme,7). The thermal cycloaddition reaction of 1 with ZSE in toluene gave the cycloadducts 2,3- exo - 22a and - 22b as well as 2- exo,3- endo - 22c in high yields (Scheme,8). All three adducts eliminated, by treatment with base, benzenesulfinic acid and yielded the corresponding 3-(phenylsulfonyl)-1,4-epoxybenzo[d]heptalenes 25. The latter turned out to be excellent Michael acceptors for H2O2 in basic media (Scheme,9). The Michael adducts lost H2O on treatment with Ac2O in pyridine and gave the 3-(phenylsulfonyl)benzo[d]heptalen-2-ones 28a and 3- exo - 28b, respectively. Rearrangement of these compounds in the presence of Ac2O/AcONa lead to the formation of the corresponding 3-(phenylsulfonyl)benzo[a]heptalene-1,2-diol diacetates 30a and 30b, which on treatment with MeONa/MeI gave the corresponding MeO-substituted compounds 31a and 31b. The reductive elimination of the PhSO2 group led finally to the 1,2-dimethoxybenzo[a]heptalenes 32a and 32b. Deprotonation experiments of 32a with t -BuLi/N,N,N,,N,-tetramethylethane-1,2-diamine (tmeda) and quenching with D2O showed that the most acid CH bond is HC(3) (Scheme,9). Some of the new structures were established by X-ray crystal-diffraction analyses (cf. Figs.,1, 3, 4, and 5). Moreover, nine of the new benzo[a]heptalenes were resolved on an anal. Chiralcel OD-H column, and their CD spectra were measured (cf. Figs.,8 and 9). As a result, the 1,2-dimethoxybenzo[a]heptalenes 32a and 32b showed unexpectedly new Cotton -effect bands just below 300,nm, which were assigned to chiral exciton coupling between the heptalene and benzo part of the structurally highly twisted compounds. The PhSO2 -substituted benzo[a]heptalenes 30b and 31b showed, in addition, a further pair of Cotton -effect bands in the range of 275,245,nm, due to chiral exciton coupling of the benzo[a]heptalene chromophore and the phenylsulfonyl chromophore (cf. Fig.,10). [source] Metal Complexes of Functionalized Sulfur-Containing Ligands.HELVETICA CHIMICA ACTA, Issue 7 2003Part XIX The title compounds were prepared starting from the dihydropyrrolones 4,6. Nucleophilic displacement and ring closure yielded the 1H -pyrrolo[3,2- c]isothiazol-5(4H)-ones 8 and 10. The fused systems formed salts with strong acids and electrophiles (15, 16), as well as with bases. Oxidation led either to S(2)-oxides (18a, 20a) or to the corresponding bicyclic sultams (18b, 20b), depending on the reaction conditions. The sulfinamide 18a was also obtained from the known 1,2-dithiolopyrrolone S -oxide 21 by a ring-opening/ring-closure reaction sequence. O -Methylation of 8 furnished the ,azafulvene' 17. The oxidative addition of [Pt(,2 -C2H4)L2] (24a: L=Ph3P, 24b: L=1/2,dppf, 24c: L=1/2,(R,R)-diop) to 18a and 20a led to the cis -amido-sulfenato Pt complexes 25 and 26a,c, respectively. [source] Enders' SAMP-Hydrazone as Traceless Auxiliary in the Asymmetric 1,4-Addition of Cuprates to EnonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Karsten Sammet Abstract Conjugate additions of Gilman cyanocuprates to (S)- N -amino-2-(methoxymethyl)pyrrolidine (SAMP)-hydrazones 4, 5 derived from cyclic and acyclic ,,,-unsaturated ketones were investigated. A protocol utilizing copper(II) sulfate/ammonium chloride was evolved, which allowed cleavage of SAMP (S)- 1 under the hydrolysis and work-up conditions, followed by recovery of the auxiliary with ethylenediaminetetraacetic acid (EDTA). The enantioselectivity of cuprate additions was dominated for cyclic SAMP-hydrazones 4 by the cuprate alkyl substituent and the ring size, in the case of acyclic arylidene SAMP-hydrazones 5, however, by the nature of the aryl substituent. Electron-donating substituents gave poor enantiomeric excesses, whereas electron-withdrawing groups provided excellent ee values of 98,99%. The configuration of the new stereocenter was determined to be (R). Moreover, a reaction sequence was developed which integrates a tandem 1,4-addition/methylation and traceless hydrolytic cleavage of the auxiliary (S)- 1 in a one-pot reaction, resulting in enantiomerically pure methyl ketones 11,13, each of them with>99% ee. [source] | |||||||||||||||||||||||||||||||