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Cope Rearrangements (cope + rearrangement)
Selected AbstractsSequential Platinum-Catalyzed Cycloisomerization and Cope Rearrangement of Dienynes,ANGEWANDTE CHEMIE, Issue 2 2010Sun Young Kim Mit Enin geht,s rund: Die Titelreaktionen ergeben bicyclische Systeme wie Bicyclo[3.2.2]nonadiene 1 oder tetrahydrierte kondensierte Ringe 2 in hohen Ausbeuten (siehe Schema; Z=NTs, O, CH2). [source] W(CO)5(L)-Catalyzed 6-endo-Selective Cyclization and Formal Cope Rearrangement of Allenyl Silyl Enol Ethers.CHEMINFORM, Issue 18 2007Tomoya Miura 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] New Chiral Synthons for Efficient Introduction of Bispropionates via Stereospecific Oxonia,Cope Rearrangements.CHEMINFORM, Issue 31 2006Yi-Hung Chen 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] Gas-Phase Electron-Diffraction Investigation and Quantum-Chemical Calculations of the Structure of 1,5-Dimethylsemibullvalene-2,4,6,8-tetracarboxylic DianhydrideHELVETICA CHIMICA ACTA, Issue 5 2003Svein Samdal The bridged homotropilidines have been of interest for decades because their molecules offer the potential for homoaromaticity. Although many of these have been shown not to be homoaromatic, the energy differences of the delocalized (homoaromatic) forms and the localized (nonhomoaromatic) ones, and the barriers to the interconversion of the localized forms via a Cope rearrangement, have been found to vary greatly. The title compound is a strong candidate for homoaromaticity, and, since the structures of the possible localized and delocalized forms could differ significantly, we have carried out an electron-diffraction investigation of it augmented by quantum-mechanical calculations with different basis sets at several levels of theory. Three models were explored: one representing a localized form of Cs symmetry, one a delocalized form of C2v symmetry, and one a 2,:,1 mixture of the localized/delocalized forms. Although none of the models could be ruled out, the experimental evidence slightly favors the Cs form. These results are consistent with those from the DFT B3PW91 calculations with basis sets ranging from 6-31G(d) to cc-pVTZ, which, surprisingly, predict essentially equal thermally corrected free energies for each. The results are discussed. [source] A joint study based on the electron localization function and catastrophe theory of the chameleonic and centauric models for the Cope rearrangement of 1,5-hexadiene and its cyano derivativesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2005Victor Polo Abstract A novel interpretation of the chameleonic and centauric models for the Cope rearrangements of 1,5-hexadiene (A) and different cyano derivatives (B: 2,5-dicyano, C: 1,3,4,6-tetracyano, and D: 1,3,5-tricyano) is presented by using the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT) on the reaction paths calculated at the B3LYP/6-31G(d,p) level. The progress of the reaction is monitorized by the changes of the ELF structural stability domains (SSD), each being change controlled by a turning point derived from CT. The reaction mechanism of the parent reaction A is characterized by nine ELF SSDs. All processes occur in the vicinity of the transition structure and corresponding to a concerted formation/breaking of C1C6 and C3C4 bonds, respectively, together with an accumulation of charge density onto C2 and C5 atoms. Reaction B presents the same number of ELF SSDs as A, but a different order appears; the presence of 2,5-dicyano substituents favors the formation of C1C6 bonds over the breaking of C3C4 bond process, changing the reaction mechanism from a concerted towards a stepwise, via a cyclohexane biradical intermediate. On the other side, reaction C presents the same type of turning points but two ELF SSD less than A or B; there is an enhancement of the C3C4 bond breaking process at an earlier stage of the reaction by delocalizing the electrons from the C3C4 bond among the cyano groups. In the case of competitive effects of cyano subsituents on each moiety, as it is for reaction D, seven different ELF SSDs have been identified separated by eight turning points (two of them occur simultaneously). Both processes, formation/breaking of C1C6 and C3C4 bonds, are slightly favored with respect to the parent reaction (A), and the TS presents mixed electronic features of both B and C. The employed methodology provides theoretical support for the centauric nature (half-allyl, half-radical) for the TS of D. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1427,1437, 2005 [source] An Unexpected Michael,Aldol,Smiles Rearrangement Sequence for the Synthesis of Versatile Optically Active Bicyclic Structures by Using Asymmetric OrganocatalysisCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2010Nicole Holub Dr. Abstract A facile and simple organocatalytic procedure to generate optically active 6-alkyl- and 6-aryl-substituted bicyclo[2.2.2]oct-5-en-2-ones is presented. The reaction is catalysed by a 9-amino-9-deoxyepiquinine trifluoroacetic acid salt, which activates ,,,-unsaturated cyclic ketones for the 1,4-addition of ,-keto benzothiazoyl sulfones in a stereoselective fashion. Subsequent intramolecular aldol reaction and Smiles rearrangement gives rise to important optically active bicycles, which are a common motif in natural products, ligands in asymmetric catalysis and substrates for Cope rearrangements, photochemical reactions, radical cyclisations and metathesis. Different bicyclic structures were obtained by utilisation of various cyclic enones or by performing ring-expanding reactions. Furthermore, two possible mechanistic pathways are outlined and discussed. [source] Organocatalytic Multicomponent ,-Methylenation/Diels,Alder Reactions: A Versatile Route to Substituted Cyclohexenecarbaldehyde DerivativesCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2008Yue Zou Abstract This article describes the design and optimization of an effective organocatalytic three-component domino ,-methylenation/Diels,Alder reaction to produce vinyl-substituted cyclohexenecarboxaldehydes in a highly regioselective fashion. In these one-pot transformations, 2-formyl-1,3-butadienes (4) were prepared in situ from ,,,-unsaturated aldehydes and formalin and were subsequently trapped with a variety of buta-1,3-dienes. The outcomes of the reactions were dependent on the electronic properties of the dienes. 1-Vinylcyclohexenecarbaldehydes 6 were formed by use of acyclic electron-rich dienes, while the initially formed cycloadducts of 4 with cyclopentadiene underwent Cope rearrangements, leading to the formation of tetrahydro-3H -indene-5-carbaldehyde compounds 7. The mechanisms involved in these reactions were deduced from experimental findings. Furthermore, the method was also extended to one-pot domino methylenation/Diels,Alder reactions of dihydrofurans and dihydropyrans to yield spirocyclic lactols 22. In these reactions, the unstable intermediate hydroxyethyl and hydroxypropyl acroleins behaved as dienophiles, undergoing cycloaddition reactions with dienes with good yields and selectivities. The wide variety of functionalized 1-vinylcyclohex-3-enecarbaldehydes 6, 4-vinylcyclohex-1-enecarbaldehydes 7, and spiro lactols 22 generated through the use of these organocatalytic domino processes as a diversity-oriented synthesis provided useful intermediates for the construction of novel odorants. [source] A Versatile Hexadiene Synthesis by Decarboxylative sp3,sp3 Coupling/Cope Rearrangement.CHEMINFORM, Issue 48 2006Shelli R. Waetzig 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] | ||||||||||