Conformational analysis-V.: A lanthanide induced shift (L.I.S.) N.M.R. investigation of conformational isomerism in aromatic aldehydes and ketones

An L.I.S. N.M.R. investigation of conformational isomerism in meta-nitrobenzaldehyde and furan- and thiophene-3-aldehydes, and of the conformation of acetophenone has been carried out. With the diamagnetic (complexation) contributions to the observed shifts removed by means of experiments with La (fod)₃ and the application of our previously-described lanthanide ion complexing model, the pseudo-contact shifts have been used to obtain the precise conformational preferences of the aldehydes. They exist to the extent of 45%, 100% and 80% respectively in the $\text{O}$-$\text{trans}$ conformation, findings which are good agreement with the previously-reported values. The L.I.S.'s for acetophenone are in best agreement with a planar molecule, although the definition is not as good in this case. These examples suggest that the L.I.S. technique is of general applicability in the determination of conformer populations and the conformations of aromatic aldehydes and ketones.     

The total synthesis of (±) kawain via a hetero-diels-alder cycloaddition

The hetero-Diels-Alder reaction between 1,3-dimethoxy-1-trimethylsilyloxybutadiene $\text{4}$, and cinnamaldehyde$\text{5}$, produces (±) kawain in 75% and 84% yield respectively when catalyzed by Eu(fod)₃ or Yb(fod)₃. When Ag(fod) is employed as the catalyst a unique condensation reaction occurs which produces two acyclic diastereomers in 72% yield.     

Influence of chemical exchange on the temperature dependence of Eu(fod)3-induced shifts

Temperature dependences of the paramagnetic shifts induced by Eu(fod)₃ in ¹H NMR spectra of ethylene oxide in carbon disulphide solution are obtained in the temperature range from +40 to ? 100°C at 100 MHz and from +30 to ?60°C at 60 MHz. The influence of chemical exchange leads to a decrease of the observed paramagnetic shifts with decreasing temperature. It is shown that a modified Swift and Connick equation can be used to describe the observed dependences. Upper limits of the mean lifetimes of the Eu(fod)₃-ethylene oxide adduct are τ_p < 1·7 × 10^?8 s at 14 °C and τ_p < 1 × 10^?8 s at 20 °C, respectively. The corresponding activation energy is equal to V_a = 13·7 kcal/mol.     

Large lanthanide-induced chemical shifts in cobalt complexes of enethials (α,β-unsaturated thioaldehydes)

Eu(fod)₃-, Yb(fod)₃- and Pr(fod)₃-induced chemical shifts of the ‘thioaldehydic’ protons in enethial ligands complexed to a cobalt cyclopentadienyl group are unusually large and in the same direction (10–30 ppm downfield per mole of shift reagent per mole of substrate). The shifts of the protons induced by Eu(fod)₃ and Pr(fod)₃ in the enethial ligands show an alternation in sign on proceeding away from the sulfur atom. In contrast to the results with the fod reagents, the ytterbium and lanthanum shift reagents Yb(thd)₃ and La(thd)₃ caused only small shifts of protons in the 2-phenylpropenethial ligand. No induced shifts with the Eu or Pr reagents were observed for a cyclopentadienyl cobalt complex of dithioglyoxal. The induced shifts in these enethial complexes may be caused by varying blends of complex formation, contact and pseudocontact shifts. Caution is advised in assigning origins to lanthanide induced shifts in such organometallic systems.     

v-Triazolines. part XXI. Spiro[bicyclo[2.2.1]hept-2-ene[54']1',2'.s'-triazole]derivatives from cyclopentadiene and 5-amino-4-methylene-v-triazolines

1R^*, 4R^*, 5S^*, 5'S^*-5'-Amino-1'-(4-nitrophenyl)-4',5'-dihydrospiro[bicyclo [2.2. 1]hept-2-ene[5.4]-1',2',3'-triazoles]$\text{2}$ have been obtained both by ?4 +2]-cycloaddition of cyclopentadiene to amino-methylene-1-(4-nitrophenyl)-4,5-dihydro-v-triazoles $\text{1}$ and by [3+2]-cycloaddition of 4-nitrophenylazide to 5-aminomethylene-2-norborenes $\text{4}$. The configuration has been fully established by X-ray crystallographic analysis. The course of the cycloaddition and the thermal behaviour of $\text{2}$ are discussed.     

XPS of coordination compounds: additive ligand effect in some copper(I) and copper(II) chelates with 1,2 phosphino (or phosphine/oxide)-sulfido ethane ligands

XPS spectra of Ph₂P-CH₂-CH₂-S-R ligands, of their P-oxides and of the corresponding 1: 2 complexes with Cu(I) and Cu(II) indicate a moderate donor shift on complexation of about 0.4 eV for S, and 0.3 eV for P on the 2p signals, and confirm complete chelation for both ligands in their metal complexes. The chemical shifts of Cu2P_{$\text{3}\text{2}$} b.e. values can be quantitatively described by a model of additive ligand contribution, for which parameter values of -0.2 eV for -S-, and -0.5+-0.6 eV for -0^? donors are proposed.     

Synthesis of 2-alkylthio (or trifluoromethylthio)-2-halogenoethenyl derivatives by means of wittig (under phase transfer conditions) or wittig-horner reactions. Application in the field of pyrethroids

A mixture of RSCHCl₂, Ph₃P and $\text{trans}$-caronaldehyde ethyl ester, treated with aq.NaOH under phase transfer conditions, gave the corresponding 2-alkylthio,2-chloroethenyl derivative, the product of the Wittig reaction of a phosphorane formed 'in situ'. The analogous derivative of the $\text{cis}$- and the 2-methylthio, 2-bromoethenyl derivative of the $\text{trans}$-caronaldehyde ethyl ester were synthesized also by means of Wittig-Horner reactions. The 2-trifluoromethylthio, 2-chloro-ethenyl derivative of the caronaldehyde ethyl ester ($\text{cis}$-$\text{trans}$ mixture) was also obtained through the phosphonate prepared from CF₃Cl + N₂CHP(OET)₂→ CF₃SCHClP(O)(OEt) The new derivatives prepared were converted to final pyrethroids by esterification with cyano(m-phenoxyphenyl)methanol.     

Synthesis and molecular structure of piplartine (=piperlongumine)

The structure of piplartine (=piperlongumine) was established as ($\text{1}$)-$\text{3}$-3',4',5'-trimethoxycinnamoyl-5,6-dihydro-2(1H)-pyridone ($\text{13}$) by synthesis and by an X-ray crystallographic analysis. Model condensation of ($\text{E}$)-3,4,5-trimethoxycinnamoyl chloride and crotonamide gave not the expected cinnamoylcrotonamide, but ($\text{1}$)-$\text{N}$-3', 4', 5' -trimethoxycinnamoyl-3-chlorobutyramide ($\text{12}$).     

Linearly and circularly polarized raman spectra of the iron (II) bis[1-(2'-pyridylmethyleneamino)-2-aminoethane] ion evidence for asymmetric raman tensor

Raman spectra of solutions of iron(II)bis[1-(2'-pyridylmethyleneamino)-2-aminoethane] iodide in acetonitrile were recorded using both linearly and circularly polarized light for excitation. The tensor invariants 45$\text{}\text{?}$ga², 7γ_s² and 5γ_as² were determined for three prominent lines with 488.0, 514.5 and 528.7 nm excitation. With two of the lines, significant anti-symmetric anisotropies are found.     

Substituent effects on fluorine - 19 chemical shifts in benzobicyclo(2.2.2)octen-1-yl fluorides

Inverse ¹⁹F substituent chemical shifts (SCS) of $\text{m}$- and $\text{p}$-substituted benzylfluorides are shown to have their origin in hyperconjugation involving the CF δ - bond.     

Synthesis of streptococci phosphatidyl-α-diglucosyldiglyceride and related glycolipids : Application of the tetraisopropyldisiloxane-1,3-diyl (tips) protecting group in sugar chemistry. Part V

A short and convenient synthesis of phosphatidyl-α-diglucosyldiglyceride (i.e. compound $\text{8d}$) and two related Streptococci glycolipids (i.e. compounds $\text{6a}$ and $\text{6b}$) will be presented. 4',6'-Tetraisopropyl-disiloxane-1,3-diyl (TIPS) protected α-glucosyl diglyceride (i.e. compound $\text{2}$) turned out to be a suitable protected precursor. Thus, compound $\text{2}$ was selectively condensed with glucosyl bromide $\text{3}$ to afford $\text{4}$. Removal of the protecting groups from $\text{4}$ gave glycolipid $\text{6a}$. The “dynamic” properties of the TIPS pro- tecting group were utilized to convert 4',6'-TIPS protected $\text{4}$ into 3',4'- TIPS protected derivative $\text{5a}$. Compound $\text{5a}$ could then be condensed with either a stearoyl fatty acid or a phosphatidyl moiety to give the fully protected derivatives $\text{5c}$ and $\text{8a}$, respectively. Finally, removal of all the protecting groups from $\text{5c}$ and $\text{8a}$ afforded the glycolipid $\text{6b}$ and glycophospholipid $\text{8d}$, respectively.     

Magnetic susceptibility of Co4+(d5) in octahedral and tetrahedral environments

Measurements of magnetic susceptibility on compounds containing stoichiometric Co⁴⁺ are reported. The compound Ba₂CoO₄ has the Co⁴⁺(d⁵) ion at a tetrahedral site and displays a susceptibility of the expected magnitude for $\text{S =}\text{5}\text{2}$. The compounds Ba₃Co₂CO₉ and BaCoO₃ have the Co⁴⁺ at an octahedral site and show a susceptibility expected for low spin, $\text{S =}\text{1}\text{2}$. For the low spin case significant deviations from Kotani's calculated susceptibility were observed. Improvement of the theory was made through incorporation of the effects of distortion from perfect octahedral symmetry and the inclusion of higher electronic configurations above t⁵₂ in the ²T₂ ground state. A case of low spin Ni in octahedral environment is also reported.     

Relationship between the general laws of vapor-liquid equilibria and the analytical curve of emission spectrometry

The relationship between the vapor-liquid equilibrium and the analytical curve of emission spectrometry is discussed on the basis of Hirata's equation, i.e., $\text{y}{}_1\text{y}{}_2$ = α($\text{x}{}_1\text{x}{}_2$)^β, where y is the mole fraction in the vapor phase, x in the liquid phase, α and β are constants for binary systems in a certain concentration range, and the indices $\text{1}$ and $\text{2}$ refer to the two components. Evaporation produced by different atomization-excitation systems can be characterized by apparent evaporation constants, α' and β', the values of which fall between the true values, α and β, of the normal distillation, and unity. Two powder techniques were selected representing the limiting cases: injection spark excitation (α' ≈ α, β' ≈ β) and controlled arc excitation (α' ≈ 1, β' ≈ 1). Using these excitation methods, the analytical curves of the impurities in industrial alumina and electrocorundum were studied using cup-electrode techniques with arc excitation. As a result, one of Hirata's rules could be selected for a given pair of elements. An unambiguous correlation between the properties of the analytical curves and Hirata's rules could be established.     

A thallium(I)-selective electrode based on a liquid ion-exchanger containing 0,0'-didecyldithiophosphoric acid

A liquid ion-exchange electrode containing thallium(I) 0,0'-didecyldithiophosphate in chlorocyclohexane is described. Nernstian behaviour is obtained in the pTI range 1–5.5, the slope of the calibration graph being 57.6 mV/decade change in activity at ionic strength 0.1, Alkali and alkaline earth metal cations do not interfere (K_{$\text{TI}\text{M}$} < 10^?5). Potentials are established rapidly, and are unaffected by pH in the range 5–12. In analytical applications direct potentiometry and potentiometric precipitation titrations with iodide or tetraphenylborate solutions are satisfactory. Various interfering ions can be masked with EDTA.     

Correlation between the n,π* triplet energy of some acetophenones and the corresponding electroreduction potentials

The half-wave reduction potentials, E_{$\text{1}\text{2}$}'s, of ten acetophenone derivatives have been determined in acetonitrile. A linear free-energy relationship was obtained between E_{$\text{1}\text{2}$} and the n,π^* triplet energy. This correlation enabled an estimate to be made of the n,π^* triplet energy of those acetophenones with π,π^* lowest triplet.     

Studies on metal carboxylates: XI. Reactions of rhenium carbonyl with picolinic acid and of the tungsten(I) complex [W(CO)3(pic)]n with monodentate tertiary phosphines

The reactions of the tungsten(I) complex of picolinic acid [W(CO)₃(pic)]_n with certain monodentate tertiary phosphines affords a convenient route to complexes of the types W(CO)₃(PR₃)₃ and HW(CO)₂(PR₃)₂(pic). The latter hydrido complexes of tungsten(II) have been characterized by infrared and NMR spectroscopy. The reactions of Re₂(CO)₁₀ with picolinic acid have also been investigated and the new series of rhenium(I) derivatives of the types Re(CO)₃(L)(pic), where L = py, 4-Ph-py, PPh₃ or dppe, and Re(CO)₂(L')₂(pic), where L' = PPh₃ or $\text{1}\text{2}$dppe, have been isolated and characterized.     

Preferential energy transfer from N2(A) to specific energy levels of Cu atoms

Emission spectra resulting from reaction of “clean” N₂(A³ Σ_u⁺) with copper atoms were studied using a flowing afterglow apparatus. The population distribution of the Cu states was calculated from the spectrum; it indicates that Cu atoms are excited by nearly resonant energy transfer processes. N₂(A,v') + Cu(²S_{$\text{1}\text{2}$}) → N₂(X, v) + Cu^* , and that the transfer is most efficient for N₂(A,v') → N₂(X,v) transitions with large Franck-Condon factors. The preferential energy transfer results in population inversion between some of the Cu states.     

Synthesis of the natural enantiomers of ascochlorin,ascofuranone and ascofuranol

Three fungal metabolites with a common structural feature as prenylated phenols were synthesized in their naturally occurring and optically active forms: ascochlorin [(2'$\text{E}$,4'$\text{E}$,1'$\text{R}$,2'$\text{R}$,6'$\text{R}$)-(-)-5-chloro-2,4-dihydroxy-6-methyl-3-[5'-(1',2',6'-trimethyl-3'-oxo-cyclohexyl)-3'-methyl-2', 4'-pentadienyl] benzaldehyde], ascofuranone [(2'$\text{E}$,6'$\text{E}$,1'$\text{S}$)-(-)-5-chloro-2, 4-dihydroxy-6-methyl-3-[7'-(3',3'-dimethyl-4'-oxo-2'-oxacyclopentyl)-3',7'-dimethyl -2', 6'-heptadienyl] benzaldehyde] and ascofuranol [(2'$\text{E}$,6'$\text{E}$,1'$\text{S}$,4'$\text{S}$)-(-)-5-chloro-2,4-dihydroxy-6-methyl-3-[7'-(3', 3'-dimethyl-4'-hydroxy-2'-oxacyclopentyl)-3', 7'-dimethyl-2',6'-hepta-dienyl]benzaldehyde ]. (+)-Ascofuranone and (+)-ascofuranol were also synthesized. By the present synthesis the absolute configuration of the natural (-)-ascofuranol was established as (1'$\text{S}$,4'$\text{S}$).