Filters
Results 1 - 10 of 656
Results 1 - 10 of 656.
Search took: 0.027 seconds
| Sort by: date | relevance |
[en] Elimination reactions of (E)-2,4,6-(NO_2)_3C_6H_2CH=NOC(O)C_6H_4X (3) promoted by R_2NH/R_2NH_2"+ in 70 mol% MeCN (aq) have been studied. The reactions produced elimination products and exhibited second-order kinetics. The β and |β_l_g| values remained nearly the same for all leaving groups and bases. The results can be described by the negligible p_x_y interaction coefficient, p_x_y = ∂β/∂pK_l_g = ∂β_l_g/∂pK_B_H ≈ 0, which provides a strong support for the (E1cb)_i_r_r mechanism. For eliminations from (E)-ArCH=NOC(O)C_6H_4X (1, 3) and (E)-2,4,6-(NO_2)_3C_6H_2CH=NOAr' (2, 3), the change of the β-aryl group (Ar) from 2,4-dinitrophenyl (1) to 2,4,6-trinitrophenyl (3) increased the rate by 270-fold without appreciable change in the transition state structure. On the other hand, the leaving group (OAr') variation from benzoate (3) to 4-nitrophenoxy (2) induced a change in reaction mechanism from (E1cb)_i_r_r to E2. These results have been attributed to the cyclic transition state for the nitrile-forming eliminations involving the benzoate leaving group.
Journal
Bulletin of the Korean Chemical Society; ISSN 0253-2964; 
; v. 37(6); p. 871-876
; v. 37(6); p. 871-876
[en] The new electrochemically induced multicomponent assembling was found: the electrocatalytic transformation of benzaldehydes, N,N′-dimethylbarbituric acid, and kojic acid has been carried out in alcohols in an undivided cell in the presence of sodium halides with the selective formation of the earlier unknown substituted 5-[[3-hydroxy-6-(hydroxymethyl)-4-oxo-4H-pyran-2-yl](phenyl)methyl]-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-triones in 65–88% yields and with 325–440% current efficiency. This new multicomponent process provides facile and efficient way to the novel type of separated by C-aryl-substituted spacer both 4-oxo-4H-pyran and 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione pharmacology active systems, which are promising compounds for different biomedical applications. Graphic abstract:
Journal
[en] We have studied the nitrile-forming elimination reactions from 1 promoted by R2NH in MeCN. The reaction proceeded by (E1cb)irr mechanism. Change of the β-aryl group from 2,4-dinitrophenyl to a more strongly electron-withdrawing 2,4,6-trinitrophenyl increased the reaction rate by 470-fold, shifted the transition state toward more reactant-like, and changed the reaction mechanism from E2 to (E1cb)irr. To the best of our knowledge, this is the first example of nitrile-forming elimination reaction that proceeds by the (E1cb)irr mechanism in MeCN. Noteworthy is the carbanion stabilizing ability of the 2,4,6-trinitrophenyl group in aprotic solvent. Nitrile-forming elimination reactions of (E)-benzaldoxime derivatives have been extensively investigated under various conditions. The reactions proceeded by the E2 mechanism in MeCN despite the fact that the reactants have syn stereochemistry, poor leaving, and sp2 hybridized β-carbon atom, all of which favor E1cb- or E1cb-like transition state. Moreover, the transition state structures were relatively insensitive to the variation of the reactant structures. The results have been attributed to the poor anion solvating ability of MeCN, which favors E2 transition state with maximum charge dispersal. For eliminations from strongly activated (E)-2,4-(NO2)2C6H3CH=NOC(O)C6H4X, a change in the reaction mechanism from E2 to (E1cb)irr was observed as the base-solvent was changed from R2NH in MeCN to R2NH/R2NH2+ in 70 mol % MeCN(aq). A combination of a strong electron-withdrawing β-aryl group and anion-solvating protic solvent was required for the mechanistic change
Journal
Bulletin of the Korean Chemical Society; ISSN 0253-2964; ; v. 31(4); p. 1043-1046
; v. 31(4); p. 1043-1046
[en] The nickel-catalyzed reaction of 1,1'-bis(dimethylsilyl)ferrocene (1) with carbonyls such as benzaldehyde, 4-cyanobezaldehyde, trimethylacetaldehyde, acetophenone, and benzophenone afforded 3-oxa-2,5-disilacyclo-1,1'-ferrocene. In contrast, the reaction of (1) with isobutyraldehyde under the same reaction condition yielded the diinsertion products formed via the insertion of two aldehyde ligands into the Si-H bond of 1,1'-bis(dimethylsilyl)ferrocene
Journal
Journal of the Korean Chemical Society; ISSN 1017-2548; ; v. 46(2); p. 139-144
; v. 46(2); p. 139-144
[en] The reactions of various substituted methylpyrimidines and bicyclic 1,2,4-triazolo[1,5-a] pyrimidines containing methyl groups in the pyrimidine ring with substituted benzaldehydes and heterocyclic aldehydes of the pyrazole and furan series have been studied. As a result, a series of styryl- and vinyl pyrimidine derivatives containing conjugated π-bonds were synthesized. In some examples, in particular, in the reaction of 2-hydroxy-4-methyl-6-phenylpyrimidine with para-dimethylamino- and para-diethylaminobenzaldehydes not styryl derivatives were isolated but the addition products of the starting reagents – 2-hydroxy-4-[(2-(4-dialkylamino)-phenyl)-2-hydroxyethyl)]-6-phenylpyrimidines, i.e. the hydration products of the expected styryl derivatives
Journal
[en] The reaction of 6-chloro-2-hydrazinoquinoxaline 4-oxide (10) with acetylacetone or dibenzoylmethane gave 6-chloro-2-(3,5-disubstituted pyrazol-1-yl)quinoxaline 4-oxide (11) through the intramolecular cyclization. The chlorination of compound 11 with phosphoryl chloride afforded 3,6-dichloro-2-(3,5-disubstituted pyrazol-l-yl)quinoxalines (12), whose reaction with hydrazine hydrate provided 6-chloro-3-hydrazino-2-(3,4-disubstituted pyrazol-l-yl)quinoxalines (13). The reaction of compound 13 with substituted benzaldehydes, benzenesulfonyl chloride, substituted benzoyl chlorides or acyl chlorides gave novel pyrazolylquinoxalines
Journal
Journal of the Korean Chemical Society; ISSN 1017-2548; ; v. 44(3); p. 229-236
; v. 44(3); p. 229-236
[en] The preparation of [5-C14]-TTC, [5, 5'-di-C14]NT (neotetrazolium) and [5, 5'-di-C14]-BT (tetrazolium blue) starting from benzaldehyde- [1-C14] has been accomplished. The yields for both mono- and ditetrazolium salts are high, and the products can be obtained with high sp. activity. The purity of the samples was investigated by paper chromatography. In the case of ditetrazolium salts some impurities could be detected and conclusions drawn as to their structure and quantity. A method has been developed to prepare C14- labelled ditetrazolium salts of high purity. The formation of the formazan, the precursor of the tetrazolium salt, goes through an unstable intermediate of tetrazene-type structure which rearranges rapidly in basic medium, to yield the formazan. The tetrazene intermediate can be isolated under suitable conditions. By using C14-labelled benzaldehyde phenylhydrazone this rearrangement was investigated and a verification of its intramolecular character given. (author)
[fr]
On a procede a la preparation de [5-C14]-TTC, de [5,5'-di-C14] NT (neotetrazolium) et de [5,5'-di-C14]-VT (bleu de tetrazolium), en partant du benzaldehyde-[1-C14]. On a pu obtenir un grand rendement, tant pour les sels de monotetrazolium que pour les sels de ditetrazolium, et des produits d'une activite specifique elevee. La purete des echantillons a ete examinee par chromatographie sur papier. Dans le cas des sels de ditetrazolium, on a pu deceler quelques impuretes et tirer des conclusions quant a leur structure et quantite. On a mis au point une methode permettant de preparer des sels de ditetrazolium marques au carbone-14 et presentant une grande purete. Dans la synthese du formazan, precurseur du sel de tetrazolium, on obtient un produit intermediaire instable d'une structure analogue a celle du tetrazene; ce produit se transforme rapidement en milieu alcalin pour donner du formazan. Le tetrazene intermediaire peut etre isole dans des conditions appropriees. On a etudie cette transformation en utilisant du benzaldehyde-phenylhydrazone marque au carbone-14, et l'on a pu verifier ainsi qu'il s'agit d'une reaction intramoleculaire. (author)[es]
Partiendo del benzaldehido-(1-14C), el autor ha sintetizado el TTC-(5-14C), el NT-(5, 5'-di-14C) (neotetrazolio) y el BT- (5, 5'-di-14C) (azul de tetrazolio). Las sales de mono- o ditetrazolio se obtienen con buen rendimiento y se logran productos de elevada actividad especifica. El autor determino la pureza de las muestras por cromatografia sobre papel. En las sales de ditetrazolio encontro algunas impurezas, que consiguio determinar cuantitativamente; asimismo establecio algunas caracteristicas de sus estructuras. Por otra parte, elaboro un metodo para obtener sales de ditetrazolio marcadas con 14C de elevada pureza. En la sintesis del formazan, el precursor de la sal de tetrazolio, se obtiene un producto intermedio inestable cuya estructura es similar a la del tetraceno. Este compuesto sufre una rapida transposicion en medio alcalino para dar lugar al formazan. Es posible aislar el producto intermedio si se trabaja en condiciones adecuadas. El autor estudia la transposicion utilizando la fenilhidrazona del benzaldehido marcado con 14C, y ha podido comprobar que se trata de una reaccion intramolecular. (author)[ru]
Iskhodya iz benzal'degida - [1-C14] udalos' izgotovit' [5-C14]-TTC, [5,5'di-C14]-NT (neoterazolij) [5,5'di-C14]-BT (sinij tetrazolij). Vykhody kak dlya monotetrazoliya, tak i dlya ditetrazoliya dostatochno znachitel'ny i produkty mogut byt' polucheny s bol'shoj udel'noj aktivnost'yu. Stepen' chistoty obraztsov byla issledovana pri pomoshchi khromatograficheskoj bumagi. V solyakh ditetrazoliya bylo obnaruzheno nekotoroe kolichestvo primesej, chto pozvolilo vyvesti zaklyucheniya otnositel'no ikh struktury i kolichestva. Byl vyrabotan metod mechennykh C14 solej ditetrazoliya vysokoj chistoty. Obrazovanie formazana, predshestvennika solej tetrazoliya, prokhodit cherez neustojchivuyu promezhutochnuyu stadiyu strukturnogo tipa tetrazona, bystro peregruppiruyushchegosya v shchelochnoj srede, chtoby dat' formazan. V podkhodyashchikh usloviyakh promezhutochnyj tetrazon mozhet byt' otdelen. Ispol'zovanie mechennogo C14 benzal'degidfenilgidrazoniya pozvolilo issledovat' ehtu peregruppirovku i proverit' ukazyvaemuyu mezhmolekulyarnuyu strukturu. (author)Source
International Atomic Energy Agency, Vienna (Austria); United Nations Educational, Scientific and Cultural Organization, Paris (France); 652 p; Mar 1962; p. 91-96; Conference on the Use of Radioisotopes in the Physical Sciences and Industry; Copenhagen (Denmark); 6-17 Sep 1960; ISSN 0074-1884; ; 1 fig, 2 tabs, 16 refs
; 1 fig, 2 tabs, 16 refs
[en] Nickel(II) complexes of the following Schiff base ligands derived from 4 (dimethylamino)benzaldehyde were synthesised: (Z)-1-(4-(dimethylamino)benzylideneamino)- propan-1-ol through condensation with 1-amino-propan-1-ol, (N1E,N2E)-N1,N2-bis(4- dimethylamino)benzylidene)benzene-1,2-diamine through condensation with benzene-1,2-diamine and 2-((4-dimethylamino)benzylidene)amino)phenol through condensation with 2-aminophenol. The synthesised Schiff bases and the resultant Ni(II) complexes were all isolated as crystals and characterized by melting point, elemental analysis, infrared spectroscopy, NMR spectroscopy, mass spectrometry and by conductance measurements. Antioxidant activity of the Ni(II) complexes was tested by assay with the free radical compound 2,2-diphenyl-1-picrylhydrazyl (DPPH). (author)
Journal
Journal of the Chemical Society of Pakistan; ISSN 0253-5106; ; v. 42(2); p. 238-242
; v. 42(2); p. 238-242
| 1 | 2 | 3 | Next |