Selective synthesis of (Z)-2-enynyl-2-hydroxy-imidazolidine-4,5-diones via Cu(i)-mediated multicomponent coupling of terminal alkynes, carbodiimides and oxalyl chloride

(Z)-2-Enynyl-2-hydroxy-imidazolidine-4,5-diones are synthesized via Cu(i)-mediated (Z)-selective geminal coupling among two terminal alkynes, carbodiimides, and oxalyl chloride. Further transformation is explored.

SCOPE FOR THE DEVELOPMENT OF SPECTROSCOPIC METHODS IN DETERMINATION OF STEREOCHEMISTRY OF NATURAL PRODUCTS

India is a rich country in terms of biodiversity & natural products, but very little work is carried out on stereochemical & spectroscopic studies of natural products. Isomers of natural products are found to be active, but the detection of stereochemical/spectral data is not effectively achieved. There is tremendous scope for spectroscopic methods in the determination of stereochemistry of some novel natural products particularly on J based approach (coupling constant values) which reveals about configuration, conformation and reactivity. Coupling varies with the angle between bonds, ring size affects coupling, electronegative atom reduces coupling, ? system increases geminal coupling, proton attached to same carbon can be different (diastereotopic) and can couple to one another, and we have the Nuclear Overhauser Effect. With these connections stereochemistry of some novel natural products is explained by using coupling constant values (spectroscopic methods). The present review is aimed at highlighting the significance and need of stereochemical & spectral studies of natural products which can be explored as promising drugs of the future.

Remarkably Large 15N, 13C and 18O Isotope NMR Shifts of the Mono-coordinate Phosphorus Atoms in the Compounds (Me3 Si)iPrNCP, K+[iPrNCP]-and KOCP · 2 DME (DME = 1,2-Dimethoxyethane)

The 31P and 13C NMR spectra of the heteroatom-substituted λ3-phosphaalkynes (Me3Si)- iPrNCP (1), K+ [iPrNCPl- (2) and KOCP · 2 DME (3) are described (Me = methyl; iPr = isopropyl). In addition,15N NMR data of 1 and 2 as well as further NMR results of all accessible nuclei of 1 to 3 are reported. The absolute values of the coupling constants 1J(31P13C) of 1, 2 and 3, 18.2, 45.7 and 57.2 Hz, respectively, are considerably different; the geminal coupling constants 2J( 31P15N) of the first two compounds show a decrease in the reverse order, 15.1 and 3.3 Hz. 13C, 29Si,15N, and 18O isotope effects on the nuclear shielding of the 31P nucleus in the non isotope-enriched compounds 1, 2 or 3 are presented and discussed. The [mono-13C]isotopomers of 1, 2 and 3 exhibit extremely negative 31P13C one-bond isotope shifts varying from -211 to -223 ppb. Remarkably, for 1 and 2 large two-bond 31P15N isotope shifts of -32 and -84 ppb, respectively, are observed. An unexpectedly large two-bond 31P180 isotope effect of -124 ppb was assigned to the [mono-180]isotopomer of compound 3. A three-bond 31P13C isotope shift of -27 ppb was found in 2.

Geometrical isomerism and 19F NMR spectroscopy of octahedral perfluoroethyl- and perfluoropropyl-substituted β-diketonates and monothio-β-diketonates of rhodium(III)

In solution in acetone at room temperature, tris(perfluoropropanoyl and perfluorobutanoyl)benzoylmethanate complexes of rhodium(III) are shown by 19F NMR spectroscopy to exist as nearly statistical 1:3 mixtures of their respective fac and mer octahedral isomers, whereas the analogous perfluoroalkanoylthiobenzoylmethanate complexes have a fac-octahedral structure. For all four complexes studied, vicinal F-F coupling constants are too small (0-3 Hz) to lead to resolved multiplet peaks, so that perfluoroethyl groups show singlet resonances for their CF3 groups. Since four-bond coupling constants are significantly larger, ~9 Hz, perfluoropropyl groups show the expected multiplet resonances for their CF3 groups. In acetone, AB patterns, with geminal coupling constants equal to approx. 270 Hz, are observed for the CF2 groups next to the chelate ring (except for the perfluoropropanoylthiobenzoylmethanate complex). (These observations are modified by solvent. In toluene, one of the AB patterns of a mer-octahedral complex collapses to a single peak.) The AB spectra, which are subject to substituent and solvent effects, can be interpreted in terms of perfluoroalkyl groups rotating rapidly about the Cring-Calkyl bond, with an unsymmetric double potential well, giving unequal rotamer populations. Changes in the spectra were not noticeable over the temperature range accessible in the acetone and toluene solvents used.Key words: rotation, perfluoroalkyl groups, fluorine NMR spectra, fluorine-fluorine coupling constants, fluorinatedβ-diketonate complexes, monothio-beta-diketonates, rhodium complexes.

Carbonyliron-Lead Complexes: Multinuclear Magnetic Resonance Study in Solution and X-Ray Structure Determination of [Et2PbFe(CO)4]2

Complexes of the types R3Pb-Fe(CO)2Cp [R=Me (a). Et (1b), iPr (lc), iBu (Id)]. R2Pb[Fe(CO)2Cp]2 [R=Me (2a), Et (2b)], iPr2(Br)Pb-Fe(CO)2Cp (3c) and [R2PbFe(CO)4]2 [R=Me (4a), Et (4b). iPr (4c)], as well as the spiro-complexes Pb[Fe(CO)4PbR2]2 [R = Me (5a). Et (5b). iPr (5c)] and Pb[Fe(CO)4]4 (6) were studied by multinuclear magnetic resonance spectroscopy (1H. 13C, 207Pb NMR). For the first time, coupling constants 1J(207Pb57Fe) were determined, covering a range between 33.5 (6) and 117 Hz (4a). The magnitude of the geminal coupling constants ∣2J(207Pb207Pb) ∣ in the spiro-compounds 5 decreases from 1090.0 Hz (5a) to 377.0 Hz (5c). The signs of the coupling constants nJ(207Pb13C(R)) (n = 1, 2) and nJ(207Pb1H(R)) (n = 2, 3) were determined by various 2D NMR experiments. Among all known Pb(IV) compounds the lowest 207Pb nuclear magnetic shielding was found in Pb[Fe(CO)4]4 (6): δ207Pb +3586.6. According to the single crystal X-ray structure determination of 4b (orthorhombic; space group Pbca; a = 967.4, b = 1367.7, c = 1772.4 pm), the Pb2Fe2 ring is planar with bond angles FePbFe = 102.8° and PbFePb = 77.2°, and there is a relatively short transannular distance of 340.8 pm between the two lead atoms.

Notizen: Geminal Coupling Constants 2.J(15N13C) in 2-Substituted Pyridines, Measured by Hahn-Echo Extended (HEED) Pulse Sequences

Coupling constants 2J(15N13CR) and nJ(15N1HR) in 2-substituted pyridines [R = Me (1), CH=CH2 (2), C≡CH (3), C(O)H (4), C(O)Me (5)] have been measured by using Hahn-echo extended (HEED) pulse sequences for one- (1 D) and two-dimensional (2D) 13C/1H NMR (HEED-INEPT, HEED-HETCOR). The magnitude of |2J(15N13CR)| is hardly affected by the hybridization of 13CR. 15N NMR spectra, measured under conditions of ultra high resolution (UHR) confirm the values 2J(15N13CR). 2D 13C/1H HEED-HETCOR experiments show that the sign of 3J(15Ν1HR) is negative in 1, whereas the coupling constants 3J(15N1HR) in 4 and 4J(15N1HR) in 3 have a positive sign

119Sn NMR Spectroscopy of Some Iron-Tin Compounds – First Measurements of One-Bond Coupling Constants 1J(119Sn57Fe), Geminal Coupling Constants 2J(119SnFe119Sn) and the Dependence of 119Sn Chemical Shifts on the Nature of the Sn–Fe Bond

Carbonyliron tin complexes CpFe(CO)2–SnMe3 (1), cis-(CO)4Fe(SnMe3)2 (2), cis-(CO)4Fe(SnMe2Cl)2 (3), [R2SnFe(CO)4]2 (4a, R = Me; 4b, R = Bu), {Me2Sn[Fe(CO)4]2}2Sn (5), Me2Sn[Fe(CO)4]2Sn[Fe(CO)4]2 (6) and Sn[Fe(CO)4]4 (7) were studied by 119Sn NMR. It proved possible for the first time to observe coupling constants 1J(119Sn57Fe) in the range of 36 to 64 Hz. The large magnitude of geminal coupling constants |2J(119SnFe119Sn)| (1400 to 1800 Hz) in the cyclic compounds 4 to 6 indicates the presence of tin-tin interactions as an efficient coupling pathway. Extreme deshielding of 119Sn nuclei in the complexes 6 (δ119Sn + 953) and 7 (δ119Sn + 1532) is associated with three-centre FeSnFe bonds in these compounds.

Eine 15N-NMR-untersuchung einiger trimethylstannylhydrazine / A15N-NMR study of some trimethylstannylhydrazines

The trimethylstannylhydrazines (Me3Sn)2N-NMe2 (1), Me3Sn(Me)N-N(Me)SnMe3 (2), (Me3Sn)2N-N(Me)SnMe3 (3), and (M e3Sn)2N-N(Ph)SnMe3 (4) have been studied by δ15N NMR at natural abundance. A correlation between δ15N of hydrazines and δI5N of corresponding am ines (replacement of one N-atom by the CH-unit) is proposed in order to estimate δI5N values and to support the non-trivial assignment of 15N resonances of hydrazines. Geminal coupling constants 2J(119SnN 15N) have been observed for the first time. Their relative magnitude is related to the probability of the N-Sn bond being in cis-position with respect to the orientation of the lone electron pair at the 15N nucleus in the 119Sn-N-15N fragment. Treatment of 4 with phenylacetylene causes non-selective cleavage of the Sn-N bonds, leading to the trim ethylstannylhydrazines 5 and 6 which have been characterized by 119Sn and 15N NMR spectroscopy in solution