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Nucleophilic Displacement (nucleophilic + displacement)
Selected AbstractsChemInform Abstract: A Straightforward Synthesis of Some Fused Aza-Arenes via Nucleophilic Displacement of a Ring Hydrogen Atom in Nitroarenes by Aromatic Hydrazone Anions.CHEMINFORM, Issue 30 2002Koji Uehata Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] Metal Complexes of Functionalized Sulfur-Containing Ligands.HELVETICA CHIMICA ACTA, Issue 7 2003Part XIX The title compounds were prepared starting from the dihydropyrrolones 4,6. Nucleophilic displacement and ring closure yielded the 1H -pyrrolo[3,2- c]isothiazol-5(4H)-ones 8 and 10. The fused systems formed salts with strong acids and electrophiles (15, 16), as well as with bases. Oxidation led either to S(2)-oxides (18a, 20a) or to the corresponding bicyclic sultams (18b, 20b), depending on the reaction conditions. The sulfinamide 18a was also obtained from the known 1,2-dithiolopyrrolone S -oxide 21 by a ring-opening/ring-closure reaction sequence. O -Methylation of 8 furnished the ,azafulvene' 17. The oxidative addition of [Pt(,2 -C2H4)L2] (24a: L=Ph3P, 24b: L=1/2,dppf, 24c: L=1/2,(R,R)-diop) to 18a and 20a led to the cis -amido-sulfenato Pt complexes 25 and 26a,c, respectively. [source] Synthesis of 1,2-Disubstituted Carbocyclic Nucleoside Analogues of CytidineHELVETICA CHIMICA ACTA, Issue 5 2006José González-Moa, María Abstract The synthesis of new 1,2-disubstituted, five- or six-ring-carbocyclic nucleoside analogues of cytidine, compounds 1 and 2a,d, are described. These compounds were obtained by aminolysis, starting from the corresponding uracil derivative, via nucleophilic displacement of a triazolyl (Scheme,1) or a (2,4,6-triisopropylphenyl)sulfonyl (TPS) group (Scheme,2) at 4-position of the pyrimidine ring. [source] 7-Halogenated 7-Deaza-2,-deoxyxanthine 2,-DeoxyribonucleosidesHELVETICA CHIMICA ACTA, Issue 6 2004Frank Seela The synthesis of the 7-halogenated derivatives 1b (7-bromo) and 1c (7-iodo) of 7-deaza-2,-deoxyxanthosine (1a) is described. A partial Br,I exchange was observed when the demethylation of 6-methoxy precursor compound 4b was performed with Me3SiCl/NaI. This reaction is circumvented by the nucleophilic displacement of the MeO group under strong alkaline conditions. The halogenated 7-deaza-2,-deoxyxanthosine derivatives 1b,c show a decreased S -conformer population of the sugar moiety compared to the nonhalogenated 1a. They are expected to form stronger triplexes when they replace 1a in the 1,dA,dT base triplet. [source] Synthesis of the Spermidine Alkaloids (,)-(2R,3R)- and (,)-(2R,3S)-3-Hydroxycelacinnine: Macrocyclization with Oxirane-Ring Opening and Inversion via Cyclic SulfamidatesHELVETICA CHIMICA ACTA, Issue 6 2003Nikolai The two epimers (,)- 1a and (,)- 1b of the macrocyclic lactam alkaloid 3-hydroxycelacinnine with the (2R,3R) and (2R,3S) absolute configurations, respectively, were synthesized by an alternative route involving macrocyclization with the regio- and stereoselective oxirane-ring opening by the terminal amino group (Schemes,2 and 6). Properly N -protected chiral trans -oxirane precursors provided (2R,3R)-macrocycles after a one-pot deprotection-macrocyclization step under moderate dilution (0.005,0.01M). The best yields (65,85%) were achieved with trifluoroacetyl protection. Macrocyclization of the corresponding cis -oxiranes was unsuccessful for steric reasons. Inversion at OHC(3) via nucleophilic displacement of the cyclic sulfamidate derivative with NaNO2 led to (2R,3S)-macrocycles. The synthesized (,)-(2R,3S)-3-hydroxycelacinnine ((,)- 1b) was identical to the natural alkaloid. [source] N - and C -acyclic thionuleoside analogues of 1,2,3-triazoleHETEROATOM CHEMISTRY, Issue 5 2004Najim A. Al-Masoudi Cycloaddition of the azide derivative 5 with 1,4-dihydroxybutyne afforded the N -thio-acyclic nucleoside 6, which prepared alternatively from coupling of the bromo derivative 8 with 2-acetoxy-ethylmercaptan. Deblocking of 6 gave the free nucleoside 7. Mesylation of 6 furnished the dimesylate 9, which gave three rearranged products 14,16 on treatment with chloride anion. These compounds might be obtained via the episulfonium ion 10, which is subjected to nucleophilic displacement and further sulfur participation. Deblocking of 14,16 afforded the free nucleoside analogues 17,19, and their structures were confirmed by COSY, ROESY, HMQC, and HMBC NMR techniques. Compound 16 was prepared alternatively from chlorination of alcohol 6 with Ph3P-CCl4. Carbomoylation of 6 led to the carbamate 20, which gave the free nucleoside analogue 21 on deblocking. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:380,387, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20030 [source] Synthesis and characterization of novel poly(arylene ether)s based on 9,10-bis-(4-fluoro-3-trifluoromethylphenyl) anthracene and 2,7-bis-(4-fluoro-3-trifluoromethylphenyl) fluoreneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Arun K. Salunke Abstract Two new bisfluoro monomers 9,10-bis-(4-fluoro-3-trifluoromethylphenyl) anthracene and 2,7-bis-(4-fluoro-3-trifluoromethylphenyl) fluorene have been synthesized by the cross-coupling reaction of 2-fluoro-3-trifluoromethyl phenyl boronic acid with 9,10-dibromo anthracene and 2,7-dibromo fluorine, respectively. These two bisfluoro compounds were used to prepare several poly(arylene ether)s by aromatic nucleophilic displacement of fluorine with various bisphenols; such as bisphenol-A, bisphenol-6F, bishydroxy biphenyl, and 9,9-bis-(4-hydroxyphenyl)-fluorene. The products obtained by displacement of the fluorine atoms exhibits weight-average molar masses up to 1.5 ×105 g mol,1 and number average molecular weight up to 6.8 × 104 g mol,1 in GPC. These poly(arylene ether)s show very high thermal stability even up to 490°C for 5% weight loss occurring at this temperature in TGA in synthetic air and showed glass transition temperature observed up to 310°C. All the polymers are soluble in a wide range of organic solvents, e.g., CHCl3, THF, NMP, and DMF. Films cast from DMF solution are brittle in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] A facile synthesis of substituted 3-amino-1H -quinazoline-2,4-dionesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2005Tuan P. Tran A new synthesis of a series of 3-amino-1H -quinazoline-2,4-diones is described. The 1H -quinazoline-2,4-dione 10 was made starting with fluorobenzoic acid in three high yielding steps. The key step of this synthesis involved the generation of the dianion of urea 7 and the subsequent intramolecular nucleophilic displacement of the 2-fluoro to form the quinazolinedione ring. The 3-amino moiety was incorporated using (2,4-dinitro-phenyl)-hydroxylamine as the aminating reagent. [source] The Hammett equation applied to the nucleophilic displacement of ions and ion pairs on substituted benzenesulphonatesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2001Sergio Alunni Abstract Nucleophilic substitution on meta - and para -substituted methyl benzenesulphonates was studied with two chloride salts with different structures: NBu4Cl or KCl-Kryptofix 2,2,2. Treating the results with the Acree equation shows that the reaction proceeds by two reaction paths, one involving the chloride ion and the other, slower one, involving the ion pairs. Treating the results with the Hammett equation gives consistent data, and shows that , is positive and nearly the same for the two reaction paths (,,,,+2). The reactivity of methyl p -nitrobenzenesulphonate was compared with that of the corresponding ethyl derivative, and it is shown that the methyl derivative reacts faster than the ethyl derivative in both paths. The results are interpreted based on the assumption that in both paths a negative charge is developed on the leaving group in the transition state, and that the activated complex is linear. Copyright © 2001 John Wiley and Sons, Ltd. [source] Synthesis and characterization of new hyperbranched poly(aryl ether oxadiazole)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2001Fang-Iy Wu Abstract A new AB2 monomer was synthesized for use in the preparation of a hyperbranched poly(aryl ether oxadiazole) with terminal phenol functionality. The AB2 monomer contains two phenolic groups and a single aryl fluoride group that is activated toward nucleophilic displacement by the attached oxadiazole ring. The nucleophilic substitution of the fluoride with the phenolate groups led to the formation of an ether linkage. Subsequently, a hyperbranched poly(aryl ether oxadiazole) having approximately a 44% degree of branching, as determined by a combination of model compound studies and 1H NMR, was obtained. The terminal phenolic groups underwent facile functionalization, furnishing hyperbranched polymers with a variety of functional chain ends. The nature of the chain-end groups had a significant influence on the physical properties of the polymers, such as the glass-transition temperature and their solubility. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3851,3860, 2001 [source] Diastereo- and Enantioselective Intramolecular [2+2],Photocycloaddition Reactions of 3-(,,-Alkenyl)- and 3-(,,-Alkenyloxy)-Substituted 5,6-Dihydro-1H -pyridin-2-onesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2010Dominik Albrecht Dr. Abstract 3-(,,-Alkenyl)-substituted 5,6-dihydro-1H -pyridin-2-ones 2,4 were prepared as photocycloaddition precursors either by cross-coupling from 3-iodo-5,6-dihydro-1H -pyridin-2-one (8) or,more favorably,from the corresponding ,-(,,-alkenyl)-substituted ,-valerolactams 9,11 by a selenylation/elimination sequence (56,62,% overall yield). 3-(,,-Alkenyloxy)-substituted 5,6-dihydro-1H -pyridin-2-ones 5 and 6 were accessible in 43 and 37,% overall yield from 3-diazopiperidin-2-one (15) by an ,,,-chloroselenylation reaction at the 3-position followed by nucleophilic displacement of a chloride ion with an ,-alkenolate and oxidative elimination of selenoxide. Upon irradiation at ,=254,nm, the precursor compounds underwent a clean intramolecular [2+2] photocycloaddition reaction. Substrates 2 and 5, tethered by a two-atom chain, exclusively delivered the respective crossed products 19 and 20, and substrates 3, 5, and 6, tethered by longer chains, gave the straight products 21,23. The completely regio- and diastereoselective photocycloaddition reactions proceeded in 63,83,% yield. Irradiation in the presence of the chiral templates (,)- 1 and (+)- 31 at ,75,°C in toluene rendered the reactions enantioselective with selectivities varying between 40 and 85,%,ee. Truncated template rac - 31 was prepared as a noranalogue of the well-established template 1 in eight steps and 56,% yield from the Kemp triacid (24). Subsequent resolution delivered the enantiomerically pure templates (,)- 31 and (+)- 31. The outcome of the reactions is compared to the results achieved with 4-substituted 5,6-dihydro-1H -pyridin-2-ones and quinolones. [source] Hydrolytic Reactions of Thymidine 5,- O -Phenyl- N -Alkylphosphoramidates, Models of Nucleoside 5,-Monophosphate ProdrugsCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2007Mikko Ora Dr. Abstract To obtain detailed data on the kinetics of hydrolytic reactions of triester-like nucleoside 5,- O -aryl- N -alkylphosphoramidates, potential prodrugs of antiviral nucleoside monophosphates, the hydrolysis of diastereomeric (RP/SP) thymidine 5,-{O -phenyl- N -[(1S)-2-oxo-2-methoxy-1-methylethyl]phosphoramidate} (3), a phosphoramidate derived from the methyl ester of L -alanine, has been followed by reversed-phase HPLC over the range from H0=0 to pH,8 at 90,°C. According to the time-dependent product distributions, the hydrolysis of 3 proceeds at pH<4 by two parallel routes, namely by nucleophilic displacement of the alaninyl ester moiety by a water molecule and by hydrolysis of the carboxylic ester linkage that allows intramolecular attack of the carboxy group on the phosphorus atom, thereby resulting in the departure of either thymidine or phenol without marked accumulation of any intermediates. Both routes represent about half of the overall disappearance of 3. The departure of phenol eventually leads to the formation of thymidine 5,-phosphate. At pH>5, the predominant reaction is hydrolysis of the carboxylic ester linkage followed by intramolecular displacement of a phenoxide ion by the carboxylate ion and hydrolysis of the resulting cyclic mixed anhydride into an acyclic diester-like thymidine 5,-phosphoramidate. The latter product accumulated quantitatively without any indication of further decomposition. Hydroxide-ion-catalyzed POPh bond cleavage of the starting material 3 occurred as a side reaction. Comparative measurements with thymidine 5,-{N -[(1S)-2-oxo-2-methoxy-1-methylethyl]phosphoramidate} (4) revealed that, under acidic conditions, this diester-like compound is hydrolyzed by PN bond cleavage three orders of magnitude more rapidly than the triester-like 3. At pH>5, the stability order is reversed, with 3 being hydrolyzed six times as rapidly as 4. Mechanisms of the partial reactions are discussed. [source] Protein Splicing Mechanisms and ApplicationsIUBMB LIFE, Issue 7 2005Francine B. Perler Abstract Inteins are protein splicing elements that employ standard enzyme strategies to excise themselves from precursor proteins and ligate the surrounding sequences (exteins). The protein splicing pathway consists of four nucleophilic displacements directed by the intein plus the first C-extein residue. The intein active site(s) are formed by folding of the intein within the precursor, which brings together the splice junctions and internal intein residues that assist catalysis. Inteins with non-canonical catalytic residues splice by modified pathways. Understanding intein proteolytic cleavage and ligation activities has led to the development of many novel applications in the fields of protein engineering, enzymology, microarray production, target detection and activation of transgenes in plants. Recent advances include intein-mediated attachment of proteins to solid supports for microarray or western blot analysis, linking nucleic acids to proteins and controllable splicing, which converts inteins into molecular switches. IUBMB Life, 57: 469-476, 2005 [source] | |||||||||||||||||||||||||