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Michael Acceptors (michael + acceptor)
Selected AbstractsEffect of the Michael Acceptor in the Asymmetric Intramolecular Stetter Reaction.CHEMINFORM, Issue 7 2004Mark S. Kerr Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Novel Bifunctional Michael AcceptorsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2004Laura Mediavilla Urbaneja Abstract The conjugated dienones 1a, 1c,e, and 1g were synthesized by aldol reaction of cyclohex-2-enones 3 with aldehydes or ketones and subsequent elimination. Whereas the acetone adducts could be converted into the desired products 1a/g by treatment with CeCl3·7H2O/NaI, the dienones 1c,e were obtained by Appel bromination and dehydrobromination with triethylamine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] ChemInform Abstract: A Homogeneous, Recyclable Rhodium(I) Catalyst for the Hydroarylation of Michael Acceptors.CHEMINFORM, Issue 26 2009Ranjan Jana 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] ,-Alkyl-,-allylation of Michael Acceptors Through the Palladium-Catalyzed Three-Component Coupling Between Allylic Substrates, Trialkylboranes, and Activated Olefins.CHEMINFORM, Issue 32 2006Nitin T. Patil 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] Cyclohexenones as Michael Acceptors in the Staunton,Weinreb Annulation: A Simple Stannane Modification for the Synthesis of Polycyclic Systems.CHEMINFORM, Issue 12 2006Bryan Hill 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] Synthesis of Anomerically Pure Vinyl Sulfone-Modified Pent-2-enofuranosides and Hex-2-enopyranosides: A Group of Highly Reactive Michael Acceptors for Accessing Carbohydrate Based Synthons.CHEMINFORM, Issue 51 2003Aditya Kumar Sanki Abstract For Abstract see ChemInform Abstract in Full Text. [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] A Three-Component Reaction Based on a Remote-Group-Directed Dynamic Kinetic Aza-Michael Addition: Stereoselective Synthesis of Imidazolidin-4-onesCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010Zhenghu Xu Dr. In control: An ,-amino amide reacted with an aldehyde and a Michael acceptor to form stable imidazolidin-4-ones with high stereoselectivity. A dynamic kinetic aza-Michael addition was discovered and applied to the three-component reaction to enforce high stereoselectivity. A remote group was incorporated to invert the reaction process and direct the reaction towards the desired product (see scheme). [source] Short and Stereoselective Total Synthesis of ,-11,13-Didehydroguaianes and -guaianolides: Synthesis of (±)-Achalensolide and (±)-Pechueloic Acid; Revision of the Structure of (+)-Rupestonic Acid,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2009Thomas Sainte-Luce Banchelin Abstract (±)-Pechueloic acid (1), (±)-rupestonic acid (3), and (±)-achalensolide (5) (guaian-8,12-olide class) were prepared stereoselectively in only nine steps from the commercially available tropylium cation via central intermediate 6, which is used as a general and efficient precursor to bicyclo[5.3.0]decane sesquiterpenes. The method does not require function protection. It is highly regio- and stereoselective thanks to an efficient C-1 epimerization, a selective C-8,9 hydrogenation, and a stereocontrolled 1,6 conjugate addition of an acrylate equivalent. These ,-11,13-didehydroguaianes and-guaianolides are good Michael acceptors and hence biologically active. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] An Expedient Synthesis of Perfluorinated Tetraazamacrocycles: New Ligands for Copper-Catalyzed Oxidation under Fluorous Biphasic ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2006Augustin de Castries Abstract Conjugate additions of cyclam to perfluorohexyl vinyl sulfone and sulfoxide, which act as efficient fluorous Michael acceptors, readily give access to new fluoro-ponytail tetraazamacrocycles in good yields. The solubility of the N -tetrasubstituted macrocycles depends dramatically on the nature of the polar function (SO or SO2): the sulfoxide cyclam derivative is soluble in perfluorodecaline (pfd) and perfluoromethylcyclohexane (pfmc) while the sulfonyl derivative is almost insoluble in organic or fluorous solvents. In agreement with the well known affinity of cyclam for copper(II) ions, stable copper complexes of the fluorous macrocyclic ligands have been isolated and characterized. In chloroform/methanol, complexes with four perfluorinated tails have been obtained from reaction of the tetra- N -perfluorohexylsulfinyl-substituted macrocycle with copper nitrate and copper perfluorocarboxylate. In trifluoroethanol, a selective retro-Michael reaction has been observed and the same reaction specifically gives copper complexes of the tri- N -substituted macrocycle. Complexes with three and four fluorous tails associated with perfluorocarboxylate counteranions are soluble in fluorous solvents (pfd and pfmc). These copper complexes were tested as catalysts for the oxidation of cyclohexene by molecular oxygen in the presence of tert -butyl hydroperoxide (tbhp). The oxidation reactions proceed under fluorous biphasic conditions and the catalyst can be recovered and reused. Quenching experiments indicate that cyclohexenyl hydroperoxide is the main oxidation product of the reaction performed with or without tbhp. Interestingly, these perfluorinated copper complexes are good, recyclable catalysts for the oxidation of cyclohexene by molecular oxygen without tbhp at room temperature and 65 °C.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [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] Organocatalyzed Conjugate Addition of Carbonyl Compounds to Nitrodienes/Nitroenynes and Synthetic ApplicationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010Sébastien Belot Abstract The purpose of this study is to point out the synthetic utility of a new class of Michael acceptors (nitrodienes and nitroenynes). The highly enantioselective organocatalytic Michael addition of carbonyl compounds to these functionalized nitroolefins has been carried out in the presence of (S)-diphenylprolinol silyl ether to achieve some interesting building blocks in high selectivities. The adducts thus obtained can be easily converted by taking advantage of the corresponding unsaturated carbon-carbon bond. In presence of the double bond, metathesis or electrophilic activation could be carried out whereas in the presence of the triple bond electrophilic activation could be conducted. We thus focused on a gold-catalyzed cyclization of the bis-homopropargylic alcohol to afford the corresponding substituted tetrahydrofuran. Then, we also demonstrated that organic and gold catalysts were compatible in a one-pot process. Indeed, we developed a one-pot enantioselective organocatalytic Michael addition to a nitroenyne followed by a gold-catalyzed acetalization/cyclization to achieve tetrahydrofuranyl ethers in high diastereo- and enantioselectivities with excellent yields. [source] Efficient synthesis of 3,5-functionalized isoxazoles and isoxazolines via 1,3-dipolar cycloaddition reactions of 1-propargyl- and 1-allylbenzotriazolesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2000Alan R. Katritzky 3-Aryl-5-(benzotriazol-1-ylmethyl)- 10a-f and 3- p -methoxyphenyl-5-(,-benzotriazol-1-yl-,-ethoxymethyl)-isoxazole (13) were prepared in high yields by 1,3-dipolar cycloadditions of 1-propargyl-benzotriazole (5) and (,-ethoxypropargyl)benzotriazole (8), respectively, with nitrite oxides 3a-f (prepared in situ from benzohydroximoyl chlorides 2a-f). The benzotriazol-1-ylmethyl moiety was further elaborated by sequential lithiation and reaction with aldehydes, alkyl halides and Michael acceptors. Similar 1,3-cycloadditions using 1-allylbenzotriazole (6) and 1-(,-ethoxyallyl)benzotriazole (7) afforded 3,5-substituted isoxazolines 11b, f and 12 in excellent yields. [source] Kinetic study of electrochemically induced Michael reactions of o -benzoquinones with 2-acetylcyclohexanone and 2-acetylcyclopentanoneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2007Davood Nematollahi Abstract The reaction of electrochemically generated o -benzoquinones (2a-f) as Michael acceptors with 2-acetylcyclohexanone (ACH) and 2-acetylcyclopentanone (ACP), as nucleophiles has been studied in various pHs using cyclic voltammetry. The results indicate that the participation of o -benzoquinones (2a-f) in the Michael reaction with acetylcyclohexanone (ACH) to form the corresponding catechol derivatives (4a-f). Based on an EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||