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Ring Nitrogen Atom (ring + nitrogen_atom)
Selected AbstractsPhosphonylation of 2-Amino- and 2-Amido-3-bromopyridines and 2-Amino-3-chloroquinoxalines with Triethyl PhosphiteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2009M. Shaker S. Adam Abstract The Tavs reaction of 2-amino- and 2-acylamido-3-bromopyridines 1 and 2 with triethyl phosphite in the presence of palladium acetate or chloride allows the synthesis of 2-amino- and 2-acylamidopyridine-3-phosphonates 3 and 4. A second ring nitrogen atom causes strong activation and leads to excellent yields in the phosphonylation of 2-amino-3-chloroquinoxalines. 2,3-Dichloroquinoxaline does not need a catalyst and undergoes double phosphonylation with sodium diethyl phosphite under Michaelis,Becker conditions. The results show an activating influence of pyridine nitrogen (,M) and deactivating influence of the amino group (+M). The reactivity of 1 and 2 in the Tavs coupling is compared with that of the 3-NH-2-bromopyridine position isomers and 2-bromoanilines and discussed in terms of the opposite effects of pyridine and amino(amido) nitrogen and different position of the N atoms towards the reaction site. The advantage of the Tavs reaction is the easy optimization because neither auxiliary ligands are required nor a base to trap the halide or a solvent. Triethyl phosphite itself acts as ligand and forms Pd0{P(OEt)3}n in the initial phase of the reaction. The structures of the products and the expected intramolecular N,H···O=P hydrogen bridging bonds were proven by solution NMR and by X-ray crystal structure analysis of single crystalline 3c.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] A theoretical density functional study of association of Zn2+ with oxazolidine and its thio derivatives in the gas phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2010Zaki S. Safi Abstract We have performed density functional theory (DFT) calculations in order to study the gas-phase interaction of oxo- and thio-oxazolidine derivatives with Zn2+. The calculations were performed at B3LYP/6-311+(2df,2p) level of theory. It has been found, in all cases, that the direct association of Zn2+ with the carbonyl and thiocarbonyl groups takes place at the heteroatom attached to position 2 irrespective of its nature. This preference has been attributed to the resonance effects caused by the nearest heteroatoms (oxygen and nitrogen). The most stable complexes correspond to structures with Zn2+ bridging between the heteroatom at position 2 or 4 of the 4- or 2-enol (or the 4- or 2-enethiol) tautomer and the dehydrogenated ring nitrogen atom, N3. Zn2+ association has a clear catalytic effect on the tautomerization processes which connect the oxo,thione forms with the enol,enethiol tautomers. Hence, although the enol,enethiol tautomers of oxazolidine and its thio derivatives should not be observed in the gas phase, the corresponding Zn2+ complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Zn2+ binding energies. Copyright © 2010 John Wiley & Sons, Ltd. [source] Metal-stabilized rare tautomers: N4 metalated cytosine (M = Li+, Na+, K+, Rb+ and Cs+), theoretical viewsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2003Majid Monajjemi Abstract Ab initio calculations indicate that metalation of the exocyclic amino group of cytosine by the elements of Group IA (Li, Na, K, Rb and Cs) induces protonation of a nucleobase ring nitrogen atom, and hence causes a proton shift from an exocyclic to an endocyclic nitrogen atom. Thus, this metal-assisted process leads to the generation of rare nucleobase tautomers. The calculations suggest that this kind of metalation increases the protonation energies of the aromatic ring of the nucleobase. The present study reports the quantum chemistry analysis of the metal-assisted tautomerization. The calculations clearly demonstrate that metalation of the exocyclic amino group of the nucleobase significantly increases the protonation energy of the aromatic rings of the nucleobase. Also, absolute anisotropy shift, molecular orbital and natural bond orbital calculations are compatible with these results. Copyright © 2003 John Wiley & Sons, Ltd. [source] Metal Complexes of 4,11-Dimethyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) , Thermodynamic and Formation/Decomplexation Kinetic StudiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2009Ivona Svobodová Abstract The macrocyclic ligand with two methylphosphonic acid pendant arms, 4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (1,8-H4Me2te2p, H4L3), was synthesized by a new simple approach. The product of the reaction of quarternized formaldehyde cyclam aminal with the sodium salt of diethyl phosphite was hydrolyzed to give a very high yield of the title ligand. The (H6L3)2+ cation in the solid state is protonated on all ring nitrogen atoms and on each phosphonate group. In the solid-state structure of [Cu(H3L3)][Cu(H2L3)]PF6·3H2O, neutral as well as positively charged complex species are present. Molecular structures of both species are very similar having the copper(II) ion in a coordination environment between square-pyramidal and trigonal-bipyramidal arrangements (, = 0.43 and 0.48) with one pendant arm non-coordinated. The ligand forms stable complexes with transition-metal ions showing a high selectivity for divalent copper atoms. The formation of complexes of the ligand with CuII, ZnII and CdII is fast, confirming the acceleration of complexation due to the presence of the strongly coordinating pendant arms. Acid-assisted decomplexation is fast for all three metal ions. Therefore, the copper(II) complex is not suitable for medicinal applications employing copper radioisotopes, but the title ligand motive can be employed in copper(II) separation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] | ||||||||||