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Common Intermediate (common + intermediate)
Selected AbstractsSynthesis of the Tetrahydroisoquinoline Alkaloid (.+-.)-Renieramycin G and a (.+-.)-Lemonomycinone Analogue from a Common Intermediate.CHEMINFORM, Issue 4 2006Philip Magnus No abstract is available for this article. [source] Synthesis of the Carbon Framework of the Stephaoxocanes Employing a Sequential RCM/Pomeranz,Fritsch ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2007Andrea B. J. Bracca Abstract The syntheses of two cyclodeca[ij]isoquinoline derivatives, which embody the carbon framework of stephaoxocanidine, excentricine and the recently isolated stephalonganines A, B and C, are reported. The target tricyclic compounds were prepared from isovanillin, employing a ring-closing metathesis approach towards the synthesis of a benzocyclodecane-type common intermediate; different modifications of thePomeranz,Fritsch protocol allowed the installation of the heterocyclic ring.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Reactions of Methyl Diazoacetate with (E)- and (Z)-1,2-Bis(trifluoromethyl)ethene-1,2-dicarbonitrile: Novel and Unanticipated Pathways,HELVETICA CHIMICA ACTA, Issue 1 2007Rolf Huisgen Abstract The cycloadditions of methyl diazoacetate to 2,3-bis(trifluoromethyl)fumaronitrile ((E)- BTE) and 2,3-bis(trifluoromethyl)maleonitrile ((Z)- BTE) furnish the 4,5-dihydro-1H -pyrazoles 13. The retention of dipolarophile configuration proceeds for (E)- BTE with >,99.93% and for (Z)- BTE with >,99.8% (CDCl3, 25°), suggesting concertedness. Base catalysis (1,4-diazabicyclo[2.2.2]octane (DABCO), proton sponge) converts the cycloadducts, trans - 13 and cis - 13, to a 94,:,6 equilibrium mixture (CDCl3, r.t.); the first step is N -deprotonation, since reaction with methyl fluorosulfonate affords the 4,5-dihydro-1-methyl-1H -pyrazoles. Competing with the cis/trans isomerization of 13 is the formation of a bis(dehydrofluoro) dimer (two diastereoisomers), the structure of which was elucidated by IR, 19F-NMR, and 13C-NMR spectroscopy. The reaction slows when DABCO is bound by HF, but F, as base keeps the conversion to 22 going and binds HF. The diazo group in 22 suggests a common intermediate for cis/trans isomerization of 13 and conversion to 22: reversible ring opening of N -deprotonated 13 provides 18, a derivative of methyl diazoacetate with a carbanionic substituent. Mechanistic comparison with the reaction of diazomethane and dimethyl 2,3-dicyanofumarate, a related tetra-acceptor-ethylene, brings to light unanticipated divergencies. [source] Substituent effect and multisite protonation in the fragmentation of alkyl benzoatesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2002Chagit Denekamp Abstract The dissociation of protonated alkyl benzoates (para H, CN, OMe and NO2) into protonated benzoic acids and alkyl cations was studied in the gas phase. It was found that the product ratio depends on the substituent at the para position of the phenyl ring. The substituent effect is probably the result of the formation of an ion,neutral complex intermediate that decomposes to an ion and a neutral, according to the relative proton affinities of the two moieties. The experimental results and theoretical calculations indicate that the favored protonation site in these compounds is the ester's carbonyl and that proton transfer from the phenyl ring to the ester group is very likely to occur under chemical ionization conditions. It is most probable that the carbonyl protonated form is a common intermediate in the fragmentation process, regardless of the protonation site. Copyright © 2002 John Wiley & Sons, Ltd. [source] Challenge of synthetic celluloseJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2005Shiro Kobayashi Abstract This article focuses on why and how the chemical synthesis of cellulose was accomplished. The synthesis of cellulose was an important, challenging problem for half a century in polymer chemistry. For the synthesis, a new method of enzymatic polymerization was developed. A monomer of ,- D -cellobiosyl fluoride (,-CF) was designed and subjected to cellulase catalysis, which led to synthetic cellulose for the first time. Cellulase is a hydrolysis enzyme of cellulose; cellulase, inherently catalyzing the bond cleavage of cellulose in vivo, catalyzes the bond formation via the polycondensation of ,-CF in vitro. It is thought that the polymerization and hydrolysis involve a common intermediate (transition state). This view led us to a new concept, a transition-state analogue substrate, for the design of the monomer. The preparation of cellulase proteins with biotechnology revealed the enzymatic catalytic functions in the hydrolysis and polymerization to cellulose. High-order molecular structures were in situ formed and observed as fibrils (cellulose I) and spherulites (cellulose II). In situ small-angle neutron scattering measurements suggested a fractal surface formation of a synthetic cellulose assembly. The principle of cellulose synthesis was extended to the synthesis of other natural polysaccharides, such as xylan and amylose, and unnatural polysaccharides. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 693,710, 2005 [source] Synthesis and Biological Activity of Some 1,3-Dihydro-2H -3-benzazepin-2-ones with a Piperazine Moiety as Bradycardic AgentsARCHIV DER PHARMAZIE, Issue 2 2010Hong-Yu Liang Abstract A series of 1,3-dihydro-2H -3-benzazepin-2-ones with a piperazine moiety were designed and synthesized by treating the common intermediate of 1,3-dihydro-7,8-dimethoxy-3-[3-(1-piperazinyl)propyl]-2H -3-benzazepin-2-ones with a variety of N -aryl-2-chloroacetamides and acyl chlorides. Their structures have been characterized by 1H-NMR, MS, and elemental analysis. The title compounds were evaluated for their bradycardic activity in vitro. Most of the synthesized compounds exhibited some vasorelaxant activity and heart-rate-reducing activity with bradycardic potency. [source] Cobalt-Mediated Linear 2:1 Co-oligomerization of Alkynes with Enol Ethers to Give 1-Alkoxy-1,3,5-Trienes: A Missing Mode of ReactivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2010David Leb, uf Dr. Abstract A variety of 1,6-heptadiynes and certain borylalkynes co-oligomerize with enol ethers in the presence of [CpCo(C2H4)2] (Cp=cyclopentadienyl) to furnish the hitherto elusive acyclic 2:1 products, 1,3,5-trien-1-ol ethers, in preference to or in competition with the alternative pathway that leads to the standard [2+2+2] cycloadducts, 5-alkoxy-1,3-cyclohexadienes. Minor variations, such as lengthening the diyne tether, cause reversion to the standard mechanism. The trienes, including synthetically potent borylated derivatives, are generated with excellent levels of chemo-, regio-, and diastereoselectivity, and are obtained directly by decomplexation of the crude mixtures during chromatography. The cyclohexadienes are isolated as the corresponding dehydroalkoxylated arenes. In one example, even ethene functions as a linear cotrimerization partner. The alkoxytrienes are thermally labile with respect to 6,-electrocyclization,elimination to give the same arenes that are the products of cycloaddition. The latter, regardless of the mechanism of their formation, can be viewed as the result of a formal [2+2+2] cyclization of the starting alkynes with acetylene. One-pot conditions for the exclusive formation of arenes are developed. DFT computations indicate that cyclohexadiene and triene formation share a common intermediate, a cobaltacycloheptadiene, from which reductive elimination and ,-hydride elimination compete. [source] The Reaction of o -Alkynylarene and Heteroarene Carboxaldehyde Derivatives with Iodonium Ions and Nucleophiles: A Versatile and Regioselective Synthesis of 1H -Isochromene, Naphthalene, Indole, Benzofuran, and Benzothiophene CompoundsCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2006José Barluenga Prof. Dr. Abstract The reaction of o -alkynylbenzaldehydes 1 with different alcohols, silylated nucleophiles 5, electron-rich arenes 10, and heteroarenes 12 in the presence of the reagent IPy2BF4, at room temperature, gave functionalized 4-iodo-1H -isochromenes 2, 6, 11, and 13 in a regioselective manner. When alkynes 16 and alkenes 19 and 20 were used as nucleophiles, a regioselective benzannulation reaction took place to form 1-iodonaphthalenes 17 and 1-naphthyl ketones 18, respectively. Moreover, the latter process has been adapted to accomplish the synthesis of indole, benzofuran, and benzothiophene derivatives (23, 27, and 28, respectively). The three patterns of reactivity observed for the o -alkynylbenzaldehyde derivatives with IPy2BF4 stem from a common iodinated isobenzopyrylium ion intermediate, A, that evolves in a different way depending on the nucleophile present in the reaction medium. A mechanism is proposed and the different reaction pathways observed as a function of the type of nucleophile are discussed. Furthermore, the reaction of the o -hexynylbenzaldehyde 1,b with styrene was monitored by NMR spectroscopy. Compound III, a resting state for the common intermediate in the absence of acid, has been isolated. Its evolution in acid media has been also tested, thereby providing support to the proposed mechanism. [source] | ||||||||||||||||||||||