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61.
4-Hydroxy-5,5-dimethylimidazolines tethered at N-1 to an aryl sulfide undergo an unprecedented acid-catalysed domino reaction, involving double methyl transposition, heterocyclisation, isomerisation of thiazetidinium ion and, finally, pi-cyclisation. In this way a one-pot synthesis of original tricyclic N,S-acetals was developed. The same triheterocyclic products can be prepared also starting from the corresponding 5-hydroxy isomers (in this case the cascade of reactions does not involve methyl transposition). 相似文献
62.
Jakubowicz K Wong YS Chiaroni A Bénéchie M Marazano C 《The Journal of organic chemistry》2005,70(19):7780-7783
[reaction: see text] 3-Alkyl-1,4-dihydropyridines dimerize in acidic medium, at low temperature, to give polycyclic imminium salts derivatives that were reduced to afford new polycyclic diamine scaffolds. The reaction can be extended to enantiopure series starting from R-(+)- or S-(-)-1-phenylethylamine. Long exposure of the polycyclic imminium salt intermediates to air moisture at 20 degrees C resulted in formation of new amide derivatives. This is probably due to the addition of water followed by an intramolecular oxido-reduction process. 相似文献
63.
Luc Maurette 《Tetrahedron》2004,60(44):10077-10098
Three different kinds of ring carbo-mers of [5]cyclitol ethers were targeted as challenging examples of functional [5]pericyclynes. Three tertiary pentaaryl-carbo-[5]cyclitol methyl ethers were synthesized through a [11+4] ring-closing double addition of triphenyl- and tri-p-anisyl-undecatetrayn-diides to dibenzoylacetylene. These compounds, obtained as oily mixtures of stereoisomers, are stable and can behave as acetylenic ligands of one or two Co2(CO)6 units. NMR analysis reveals that the broad diasteroisomeric dispersity of a triether, is consistently reduced in the symmetrized pentaether. Three bis-secondary triaryl-carbo-[5]cyclitol methyl ethers with adjacent CH(OR) vertices were synthesized through a similar [11+4] ring-closing process, where the same tetrayn-diides add to both the carbaldehyde ends of the (η2-OCH-CC-CHO)Co2(CO)6 complex. Despite the possibility of tautomeric isomerization, the occurrence of two adjacent bis-propargylic carbinol vertices does not diminish the stability of the [5]pericyclyne framework. Finally, two bis-secondary carbo-[5]cyclitol methyl ethers with non-adjacent CH(OH) vertices were synthesized through an alternative [10+5] ring-closing process. The bis-secondary carbo-[5]cyclitols are regarded as isohypsic equivalents of the challenging [C,C]5carbo-cyclopentadienyl cation. A diphenyl-hexaoxy-[5]pericyclyne with two non-adjacent secondary carbinol vertices was also prepared through a [10+5] ring-closing strategy: this molecule is an isohypsic equivalent of the previously calculated zwitterionic carbo-cyclopentadienone, which could be observed as a DCI/NH3-MS fragment after treatment with SnCl2/HCl. Analytical HPLC showed that the C11 triphenyl-undecatetrayne precursor of the [11+4] strategy was obtained as a statistical 1:2:1 mixture of the three possible diastereoisomers. Semi-preparative HPLC allowed for the resolution of this mixture. The pure major diastereoisomer was employed to prepare a partly resolved sample of pentamethoxy-pentaphenyl-[5]pericyclyne. Analytical HPLC showed that the latter corresponds to the statistical distribution of the expected three residual diastereoisomers. Semi-preparative HPLC finally afforded samples of diastereoisomerically pure pentamethoxy-[5]pericyclyne as crystalline solids. 相似文献
64.
The total synthesis of (±) dihydroreynosin and of (±) 1-oxocostic acid (R = H) are illustrative examples for a short entry into 1-oxygenated eudesmanes via an easily accessible key intermediate . 相似文献
65.
Cavé C Desmaële D d'Angelo J Riche C Chiaroni A 《The Journal of organic chemistry》1996,61(13):4361-4368
The Michael-type addition of chiral imines, derived from racemic alpha-substituted cyclanones and optically active 1-phenylethylamine, to electrophilic alkenes, in neutral conditions, constitutes one of the most efficient methods for the stereocontrolled construction of quaternary carbon centers. In order to create an additional stereogenic center at the alpha- or beta-position to the quaternary one, the behavior of a variety of alpha- and beta-substituted alkenyl acceptors was examined. In general, these additions are highly regioselective, the alkylation taking place predominantly, if not exclusively, at the more substituted alpha-side of the imine function; however, in some cases (electrophilic alkenes 28 and 49), significant amounts (10-15%) of regioisomeric adducts were obtained. With the exception of methyl propiolate 52, a remarkable control of the absolute configuration of the adducts were always observed with these Michael acceptors. According to the general rule we have previously proposed, the alkylation process takes place preferentially on the less hindered pi-face of the more substituted secondary enamine, in tautomeric equilibrium with the starting imine. An excellent diastereocontrol was always obtained by using the present alpha- and beta-substituted alkenes. These stereochemical outcomes can be interpreted by invoking that the reaction proceeds through a compact approach of the reactants, the hydrogen atom at the nitrogen center of the enamine being transferred to the alpha-vinylic carbon atom of the acceptor, concertedly with the creation of the C-C bond. In this respect the "endo-approach" 58, in which the electron-withdrawing group of the acceptor faced to the nitrogen atom of the enamine (case of acceptors 10, methyl methacrylate, 24, 28, 43, 47, and 49) largely prevails over the "exo-approach" 59 (case of acceptor 38). This predominant "endo-preference" can be reasonably interpreted in terms of a cooperative effect between steric and stereoelectronic factors. 相似文献
66.
Marie-Lise Bourguet-Kondracki Marie-Th r se Martin Mich le Guyot 《Tetrahedron letters》1992,33(52):8079-8080
Smenoqualone, a novel quinonic terpenoid with a rearranged drimane skeleton was isolated from a marine sponge Smenospongia sp. The stereostructure was determined by detailed analyses of 1H and 13C NMR spectra, 1H-1H COSY, 1H-13C correlations via HMQC, HMBC and NOE difference NMR experiments. 相似文献
67.
Poriel C Ferrand Y le Maux P Raul-Berthelot J Simonneaux G 《Chemical communications (Cambridge, England)》2003,(9):1104-1105
Anodic oxidation of tetraspirobifluorene-manganese porphyrin lead to the coating of the working electrode by insoluble electroactive poly(9,9'-spirobifluorene-manganese porphyrin) films for which electrochemical behaviour and physicochemical properties are described; these polymeric materials are able to catalyze the heterogeneous epoxidation of styrene with iodobenzene diacetate and iodosylbenzene. 相似文献
68.
69.
Maria Vittoria SpaneddaVu Dinh Hoang Benoit Crousse Danièle Bonnet-Delpon Jean-Pierre Bégué 《Tetrahedron letters》2003,44(2):217-219
Hexafluoroisopropanol and trifluoroethanol are found to promote imino-Diels-Alder reactions of the N-aryl aldimine 1 with alkyl vinyl ethers to afford the corresponding tetrahydroquinolines in good yields without Lewis acid under mild and neutral conditions. The reaction is also efficient in a three component process from aldehyde, amine and vinyl ethers. 相似文献
70.
U. Ströle 《Fresenius' Journal of Analytical Chemistry》1955,144(4):256-264
Zusammenfassung Bei der Chromatographie auf Carboxylpapier herrschen definierte Ionenaustauschvorgänge vor, die sich theoretisch näherungsweise ableiten lassen. Durch Variation von Carboxylgehalt und austauschfähigem Kation im Papier, sowie vonph-Wert, Pufferkapazität und Kationenstärke in der entwickelnden Lösung ist es möglich, die für die chromatographische Trennung der drei basischen Aminosäuren günstigsten Bedingungen festzustellen. Es ist zu erwarten, daß sich auf Carboxylpapier weitere, kationenbildende Stoffe trennen lassen, die sich entweder in ihrer Affinität zur Oxycellulose oder in ihrer Basizität oder in beidem voneinander unterscheiden.Die Arbeit wurde durch wertvolle Kritik von Herrn Professor Dr. Th. Wieland gefördert. Wesentliche Anregungen stammen auch von Herrn Dr. W. Vollmer. Im Labor wurden die Chromatogramme sämtlich von Frau E. v. Dungen ausgeführt. 相似文献