Structures of 4-Iminopyrido[1,2-a]pyrimidines, Pyrido[1,2-a]pyrimidin-4-ones, Pyridopyrimidinium Olates, and Thiazolo[3,2-a]pyrimidine Analogues

2012 ◽  
Vol 65 (4) ◽  
pp. 371 ◽  
Author(s):  
Paul V. Bernhardt ◽  
Curt Wentrup
Keyword(s):  
Nitrogen Atom ◽  
Ring Opening ◽  
Normal Range ◽  
X Ray ◽  
X Ray Crystallography ◽  
Structural Peculiarities ◽  
Ring Nitrogen ◽  
Structure Correlation ◽  
Pyrimidine Analogues ◽  
Ring Nitrogen Atom

The Structure-Correlation Principle of Bürgi and Dunitz is invoked in an analysis of the structures of 2-chloro-8-methyl-4-(2-(4-picolinyl)imino-4H-pyrido[1,2-a]pyrimidine 8, 7-chloro-5-(2-thiazolyl)imino-5H-thiazolo[3,2-a]pyrimidine 9, 2-methylamino-4H-pyrido[1,2-a]pyrimidin-4-one 10, 7-methylthio-5H-thiazolo[3,2-a]pyrimidin-5-one 11, 2,3-dihydro-7-methylthio-5H-thiazolo[3,2-a]pyrimidin-5-one 12, and 1-methyl-2-[(o-tert-butylphenyl)imino]-1,2-dihydropyrido[1,2-a]pyrimidin-1-ium-4-olate 13, which have been determined by X-ray crystallography. The most notable structural peculiarities are the long ‘amidine’ and ‘amide’ C–N bonds (1.40–1.50 Å) and the tilting of the ‘amidine’ C=N and ‘amide’ C=O groups towards a ring nitrogen atom (NCX = 114–118°). Also the ‘amidine’ C=N (1.28 Å) and ‘amide’ C=O bonds (1.22–1.24 Å) are long, i.e. in the normal range for resonance-stabilized amidines and amides in spite of the lack of such resonance in these compounds. These features mimic the transition states for ring opening to ketenes. The long amidine and amide C–N bonds and acute NCX angles are in accord with the observed thermal ring opening to ketenimines and ketenes, respectively.

Übergangsmetallkomplexe mit Nitroxidradikalen: Palladium-, Platin-, Pentamethylcyclopentadienyl-rhodium- und -iridium-Komplexe sowie α-Aminocarboxylatkomplexe mit Donor-haltigen Derivaten des 2,5-Dihydroimidazol-l-oxyls / Transition Metal Complexes of Nitroxide Radicals, Palladium, Platinum, Pentamethylcyclopentadienyl Rhodium and Iridium Complexes, and α-Aminocarboxylate Complexes with Derivatives of 2,5-Dihydroimidazole-l-oxyls

1998 ◽  
Vol 53 (1) ◽  
pp. 101-109 ◽  
Author(s):  
Frank Hintermaier ◽  
Sylvia Helding ◽  
Leonid B. Volodarsky ◽  
Karlheinz Sünkel ◽  
Kurt Polbom ◽  
...  
Keyword(s):  
Nitrogen Atom ◽  
Molecular Structures ◽  
Iridium Complexes ◽  
X Ray Diffraction ◽  
Chelate Complexes ◽  
X Ray ◽  
Ring Nitrogen ◽  
Derivatives Of ◽  
Ring Nitrogen Atom ◽  
Palladium Platinum

2,5-Dihydroimidazoline-l-oxyl radicals I, II with imino substituents coordinate to Pd(II) and Pt(II) complexes with formation of the N,N chelate complexes 1-6. With oxygen containing substituents either monodentate N-coordination to give 8 or N ,O chelate formation to give 9 takes place, depending on the position of the oxygen atom relative to the ring nitrogen atom. With radicals III that also have the second ring nitrogen atom oxidized and the Rh(III) or Ir(III) complexes [Cp*MCl2]2 the O , O chelates 11 -13 could be obtained, while with Na2PdCl4 the heterocycle was destroyed with formation of a N,N chelate complex 10 of an α-nitrosooxime ligand. The orthopalladated 2,2,5,5 tetramethyl-4-phenyl-2,5-dihydroimidazoline-l-oxyl complex 7a reacts with several a-amino acidates under splitting of the dichloro bridge with formation of the C,N/N,O-bis-chelate complexes 7b-f. The molecular structures of 2 and 10 were determined by X-ray diffraction.

1,5-(1,7)-Biradicals and Nitrenes Formed by Ring Opening of Hetarylnitrenes

2013 ◽  
Vol 66 (3) ◽  
pp. 286 ◽  
Author(s):  
Curt Wentrup ◽  
David Kvaskoff
Keyword(s):  
Electron Spin Resonance ◽  
Nitrogen Atom ◽  
Low Temperature ◽  
Electron Spin ◽  
Ring Opening ◽  
Matrix Isolation ◽  
Diazo Compounds ◽  
Spin Resonance ◽  
Ring Nitrogen ◽  
Ring Nitrogen Atom

Several aromatic and heteroaromatic nitrenes and carbenes undergo photochemical and sometimes also thermal ring opening. Depending on benz-annelation, the ring-opened species may have the character of either nitrenes (for α-annelation) or 1,5-(1,7-)-biradicals (for β-annelation). Both types have been observed, and they are clearly distinguished by their characteristic electron spin resonance spectra. In addition, ring opening of hetarylnitrenes to nitrile ylides can be observed whenever there is a meta-relationship between a ring nitrogen atom and the nitrene (or carbene) centre. The factors governing the two types of ring opening have been investigated. The nitrenes and carbenes are generated by either low temperature Ar matrix photolysis or flash vacuum thermolysis of azides, tetrazoles, triazoles, or diazo compounds with matrix isolation of the products.

Reaction of Imidazoles with Cyanogen Bromide: Cyanation at N 1 or Bromination at C 2?

1999 ◽  
Vol 52 (3) ◽  
pp. 159 ◽  
Author(s):  
Peter B. W. McCallum ◽  
M. Ross Grimmett ◽  
Allan G. Blackman ◽  
Rex T. Weavers
Keyword(s):  
Nitrogen Atom ◽  
Cyanogen Bromide ◽  
Lone Pair ◽  
Alkyl Substituent ◽  
Acetonitrile Solution ◽  
Crystal Data ◽  
X Ray ◽  
Ring Nitrogen ◽  
Ring Nitrogen Atom

The reaction in acetonitrile solution of a number of imidazoles(1H-, 1-methyl-, 2-methyl-, 4-methyl-, 1,2-, 1,4- and1,5-dimethyl-, 1-ethyl-, 1-benzyl- and 1-butyl-imidazole) and imidazolecomplexes([Co(NH3)5(imH)](ClO4)3,[Co(NH3)5(im)](ClO4)2 and[Co(NH3)5(1-Meim)](ClO4)3) with BrCN has beenstudied. Those imidazoles bearing an N-alkyl substituent and having a hydrogenat C2 react to give the 2-bromo products, while the N-H imidazoles react togive N-cyano derivatives. The product(s) from thereaction of 1,2-dimethylimidazole with BrCN could not be characterized. Of thecomplexes, only[Co(NH3)5(im)](ClO4)2 reacts, giving the 2-bromoproduct. Our observations suggest a lone pair on a ring nitrogen atom isnecessary for an imidazole to react with BrCN, and a possible mechanism issuggested. The X-ray structure of 2-methylimidazole-1-carbonitrile isreported. Crystal data (–143°C) forC5H5N3:monoclinic, P21/c, a10·201(5), b 7·110(3),c 7·227(3) Å, β 100·47(2)°,V 515·4(4) Å 3 , Z 4,dcalcd 1·380 gcm¯3 . Refinement of the structure converged withR1 0·0444 for 1183reflections with Fo >4F(Fo) andwR2 0·1259 for all 1278data.

Structural studies of some 1-polymethyleneimino-2,4-dinitrobenzenesand related compounds; crystal structure of 1-(cis-2′,6′-dimethylpiperidin-1′-yl)-2,4-dinitrobenzene

2000 ◽  
Vol 53 (8) ◽  
pp. 715 ◽  
Author(s):  
Maureen F. Mackay ◽  
Douglas J. Gale ◽  
John F. K. Wilshire
Keyword(s):  
Crystal Structure ◽  
Phenyl Ring ◽  
Ring Opening ◽  
Boat Conformation ◽  
Structural Studies ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Mean ◽  
Related Compounds ◽  
Solid State Conformation

The ultraviolet and 1H n.m.r. spectra of some 1-polymethyleneimino-2,4-dinitrobenzenes and related compounds are discussed. The effect of trifluoroacetic acid on these spectra was also investigated; with 1-azetidinyl-2,4-dinitrobenzene, acid-catalysed ring opening was observed. The solid-state conformation of 1-(cis-2′,6′-dimethylpiperidin-1′-yl)-2,4-dinitrobenzene has been defined by single-crystal X-ray crystallography. Triclinic crystals belong to the space group P–1 with a 8.165(1), b 7.865(1), c 11.148(1) Å, α 95.23(1), β 106.00(1), γ 92.63(1)˚ and Z 2. The structure was refined to a final R of 0.048 for the 2222 observed data. In the crystal, the phenyl ring adopts a slight boat conformation, while the amino and o-nitro groups are significantly twisted from the mean plane of the ring.

scholarly journals Synthesis, biophysical properties, and RNase H activity of 6’-difluoro[4.3.0]bicyclo-DNA

2019 ◽  
Vol 15 ◽  
pp. 79-88 ◽  
Author(s):  
Sibylle Frei ◽  
Adam K Katolik ◽  
Christian J Leumann
Keyword(s):  
Building Block ◽  
Ring Opening ◽  
Structural Investigation ◽  
Cyclopropane Ring ◽  
Cd Spectroscopy ◽  
Rnase H ◽  
Biophysical Properties ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cleavage Assay

Here we present the synthesis, the biophysical properties, and the RNase H profile of 6’-difluorinated [4.3.0]bicyclo-DNA (6’-diF-bc4,3-DNA). The difluorinated thymidine phosphoramidite building block was synthesized starting from an already known gem-difluorinated tricyclic glycal. This tricyclic siloxydifluorocyclopropane was converted into the [4.3.0]bicyclic nucleoside via cyclopropane ring-opening through the addition of an electrophilic iodine during the nucleosidation step followed by reduction. The gem-difluorinated bicyclic nucleoside was then converted into the corresponding phosphoramidite building block which was incorporated into oligonucleotides. Thermal denaturation experiments of these oligonucleotides hybridized to complementary DNA or RNA disclosed a significant destabilization of both duplex types (ΔT m/mod = −1.6 to −5.5 °C). However, in the DNA/RNA hybrid the amount of destabilization could be reduced by multiple insertions of the modified unit. In addition, CD spectroscopy of the oligonucleotides hybridized to RNA showed a similar structure than the natural DNA/RNA duplex. Furthermore, since the structural investigation on the nucleoside level by X-ray crystallography and ab initio calculations pointed to a furanose conformation in the southern region, a RNase H cleavage assay was conducted. This experiment revealed that the oligonucleotide containing five modified units was able to elicit the RNase H-mediated cleavage of the complementary RNA strand.

scholarly journals Exploring the Isomer Dependent SERS Spectra of (diphenylphosphoryl)(pyridin-2, -3, and -4-yl)methanol Adsorbed on Gold Nanocolloids

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Ewa Pięta ◽  
Edyta Proniewicz ◽  
Bogdan Boduszek ◽  
Tomasz K. Olszewski ◽  
Younkyoo Kim ◽  
...  
Keyword(s):  
Nitrogen Atom ◽  
Adsorption Process ◽  
Gold Surface ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Enhanced Raman Scattering ◽  
Ring Nitrogen ◽  
Derivatives Of ◽  
Ring Nitrogen Atom ◽  
Surface Changes

The surface-enhanced Raman scattering (SERS) spectra of three aminophosphonate derivatives of pyridine: (diphenylphosphoryl)(pyridin-2-yl)methanol (α-Pyr), (diphenylphosphoryl)(pyridin-3-yl)methanol (β-Pyr), and (diphenylphosphoryl)(pyridin-4-yl)methanol (γ-Pyr) were measured after immobilization onto colloidal gold surface. Changes in the wavenumber, broadness, and enhancement between the corresponding Raman and SERS bands allowed to deduce orientation of theα-,β-, andγ-isomers (α-,β-, andγ-refer to the position of the substituent relative to the ring nitrogen atom) of aminophosphonate derivatives of pyridine on the gold surface. Briefly, it was demonstrated that theα-Pyr andβ-Pyr show the same mode of adsorption, whereas the adsorption process of theγ-Pyr isomer differs in this regard that pyridine assists in the interaction with the gold surface.

Notizen: Kristallstruktur eines mesomeren Organozinnradikals1 / Crystal Structure of a Mesomeric Organo Tin Radical

1977 ◽  
Vol 32 (3) ◽  
pp. 355-356 ◽  
Author(s):  
Wolfgang Uber ◽  
Hartmut B. Stegmann ◽  
Klaus Scheeffleb ◽  
Joachim Strähle
Keyword(s):  
Crystal Structure ◽  
Nitrogen Atom ◽  
Additional Contribution ◽  
Coupling Constant ◽  
Tin Compounds ◽  
X Ray ◽  
X Ray Crystallography

o-Aminophenols react with organo tin compounds forming stable mesomeric complexes. The structure of one compound was determined by X-ray crystallography. The tin atom is chelated by two oxygen and one nitrogen atom. The nitrogen atom and the associated C and Sn atoms are in a plane and therefore the ESR tin coupling constant has an additional contribution by a π-σ-interaction through the N—Sn bond.

Oxidation of the Ring Nitrogen Atom

2002 ◽  
pp. 1
Author(s):  
G. Hajos ◽  
Z. Riedl
Keyword(s):  
Nitrogen Atom ◽  
Ring Nitrogen ◽  
Ring Nitrogen Atom

The geometry of 4-(1-ethoxyethylidene)-5-oxazolones and thiazolones: 1H and 13C studies and the crystal structure of 4-[(Z)-1-ethoxyethylidene]-2-phenyl-5-oxazolone

1985 ◽  
Vol 63 (12) ◽  
pp. 3618-3630 ◽  
Author(s):  
R. A. Bell ◽  
R. Faggiani ◽  
C. J. L. Lock ◽  
R. A. McLeod
Keyword(s):  
Crystal Structure ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Side Chain ◽  
Oxazole Ring ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cell Dimensions ◽  
Ring Nitrogen ◽  
E And Z Isomers

A series of E and Z isomers of substituted 4-(1-ethoxyethylidene)-5-oxazolones and thiazolones have been prepared and their 1H and 13C spectra recorded. The vinylic methyl 1H chemical shifts showed minimal differences between E and Z isomers whereas the vinylic OCH21H signals differed by 0.15–0.43 ppm, with the Z isomer being consistently the more deshielded. Both vinylic methyl and OCH2 groups showed different 13C resonances for each isomer, with the Z isomers being the more deshielded. The Z geometry was conclusively defined for one isomer of 4-(1-ethoxyethylidene)-2-phenyl-5-oxazolone, 5, by X-ray crystallography and this was sufficient to assign the geometry of the remaining pairs of E and Z isomers. Oxazolone 5 has the space group P21/n and cell dimensions a = 9.219(3), b = 19.899(5), c = 7.459(1) Å, β = 118.01(2)°, and has four formula units in the unit cell. Intensities were measured with use of MoKα radiation and a Nicolet P3 diffractometer. The crystal structure was determined by standard methods and refined to R1 = 0.0709, R2 = 0.0696 based on 1419 independent reflections. The molecule is essentially planar and most bond lengths and angles are normal. Exceptions are the very short C(olefin)—O(ether) bond (1.339(4) Å) and the large ether C—O—C angle (122.1(3)°) caused by extreme delocalization in the O(ether)CCCO(carbonyl) system. The planarity causes a number of strong intramolecular repulsive interactions, causing an exceptionally small external olefin angle, O(ether)CC(methyl), of 108.1(4)°. The ethoxyl side chain of 5 adopts a conformation in the solid state which places the methylene of the OCH2 group adjacent to the oxazole ring nitrogen. This conformation is proposed to persist in solution phases and is consistent with the observed 13C chemical shifts and known γ and δ substituent effects.

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