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Exocyclic Double Bond (exocyclic + double_bond)
Selected Abstracts4- exo - dig Cyclocarbopalladation: A Straightforward Synthesis of Cyclobutanediols from Acyclic ,-Bromopropargylic Diols under Microwave Irradiation Conditions,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2006Christophe Bour Abstract Treatment of acyclic ,-bromopropargylic diols with tributylstannylated alkynes under palladium catalysis and microwave irradiation conditions gives high yields of the bis(alkylidene)cyclobutanediol derivatives and cyclobutenediols through an efficient 4- exo - dig cyclocarbopalladation. The cyclization is general with a wide variety of alkyne derivatives and gives access to new cyclobutane ring systems bearing one exocyclic double bond and one eneyne substituent as well as bicyclic dienes sharing a common double bond that may be of interest for further elaborations of complex molecules. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Enantioselective Synthesis of Chiral Tetrahydroisoquinolines by Iridium-Catalyzed Asymmetric Hydrogenation of EnaminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Pu-Cha Yan Abstract Chiral iridium complexes based on spiro phosphoramidite ligands are demonstrated to be highly efficient catalysts for the asymmetric hydrogenation of unfunctionalized enamines with an exocyclic double bond. In combination with excess iodine or potassium iodide and under hydrogen pressure, the complex Ir/(Sa,R,R)- 3a provides chiral N -alkyltetrahydroisoquinolines in high yields with up to 98% ee. The L/Ir ratio of 2:1 is crucial for obtaining a high reaction rate and enantioselectivity. A deuterium labeling experiment showed that an inverse isotope effect exists in this reaction. A possible catalytic cycle including an iridium(III) species bearing two monophosphoramidite ligands is also proposed. [source] Use of some aryl and heteroaryl nitrilimines and nitrones in the synthesis of spiroheterocyclesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2004Eva Jedlovská 1,3-Dipolar cycloadditions of C-(5-nitro-2-furyl)- N -methyl nitrilimine (2a), C -(5-nitro-2-furyl)- N -phenyl nitrilimine (2b), C -4-nitrophenyl- N -methyl nitrilimine (2c) and C,N -diphenyl nitrilimine (2d) with 1-R-substituted 3,3-methylene-5,5-dimethylpyrrolidin-2-ones (1a-d) where R is H, acetyl, 1,1-dimethylethoxycarbonyl and 1-methylethenyl proceed with complete regioselectivity in good yields to afford 1,3,7-trisubstituted-6-oxo-8,8-dimethyl-1,2,7-triazaspiro[4,4]non-2-enes (5a-g) exclusively. Cycloaddition of C -(5-nitro-2-furyl)- N -phenylnitrone (3b) to the exocyclic double bond of the dipolarophile 1a proceeds to 2-phenyl-3-(5-nitro-2-furyl)-6-oxo-8,8-dimethyl-1-oxa-2,7-diazaspiro[4,4]nonane (7) with complete regio- and stereoselectivity. [source] Conformational and tautomeric eccentricities of 2-acetyl-1,8-dihydroxynaphthalenesMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2007Poul Erik Hansen Abstract Tautomerism in aromatic systems with oxygen substitutents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen,hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3CO methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B), each having two intramolecular O···HO hydrogen bonds: one involving an acetyl oxygen and the neighboring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT). DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O -1 and O -8 centers, which is modulated by formation of an OH-1···O-8 or OH-8···O1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH···O···C hydrogen bond are other factors. Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state. Copyright © 2006 John Wiley & Sons, Ltd. [source] Two stereoisomers of the rat toxicant norbormideACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2004Peter J. Steel The structures of two diastereoisomers of norbormide {systematic name: 5-[hydroxy(phenyl)(2-pyridyl)methyl]-8-[phenyl(2-pyridyl)methylene]-3a,4,7,7a-tetrahydro-4,7-methano-1H -isoindole-1,3(2H)-dione}, viz. the unsolvated molecule, C33H25N3O3, and the ethyl acetate hemisolvate, C33H25N3O3·0.5C4H8O2, have been determined unambiguously. They differ in the relative stereochemistry about the exocyclic double bond and the relative conformations of the aryl rings. Each compound exhibits both intra- and intermolecular hydrogen bonding. [source] Synthesis and HPLC enantioseparation of the cyclopropane analogue of valine (c3Val)CHIRALITY, Issue 1 2005Ana I. Jiménez Abstract A new and efficient method is presented for the preparation of the N -Boc-protected cyclopropane analogue of valine, 1-(N-tert -butoxycarbonyl)amino-2,2-dimethylcyclopropanecarboxylic acid, both in racemic and enantiomerically pure forms. Cyclopropanation of the exocyclic double bond of 2-phenyl-4-isopropylidene-5(4H)-oxazolone with diazomethane followed by elaboration of the heterocyclic moiety provided multigram quantities of the racemic target compound. Subsequent HPLC resolution of a racemic precursor on a noncommercial chiral stationary phase has given access to enantiomerically pure products. Almost 1.5 g of the first-eluted enantiomer and 1.0 g of the second-eluted enantiomer have been isolated in optically pure form using a 150 × 20 mm ID column containing mixed 10-undecenoate/3,5-dimethylphenylcarbamate of cellulose covalently bonded to allylsilica gel with a mixture of hexanes/tert -butyl methyl ether/ethyl acetate as the mobile phase. Chirality 17:22,29, 2005. ©2004 Wiley-Liss, Inc. [source] | ||||||||||