The use of lanthanide-induced shifts for conformational and structural studies of (R)-MTPA (α-methoxy-α-trifluoromethyl-α-phenylacetic acid) esters. 2—Complexes of the (R)-MTPA esters of 4-tert-butylcyclohexanols with Eu(fod)3

It is shown that the complexation of the (R)-MTPA (α-methoxy-α-trifluoromethyl-α-phenylacetic acid) ester of cis-4-tert-butylcyclohexanol with Eu(fod)₃ is very similar to that of the corresponding trans-ester and ketones with Eu(fod)₃. Further evidence is provided that the MTPA moiety exists as two different rotamers. The LIS technique, used as a tool for structure and conformation elucidation, was found by means of a Monte Carlo error analysis not to be dependent on small experimental errors.     

Sc(OTf)3-catalyzed intramolecular aza-Prins cyclization for the synthesis of heterobicycles

The coupling of (E)- and (Z)-hex-3-ene-1,6-ditosylamide with various aldehydes in the presence of 10 mol % Sc(OTf)₃ gave the corresponding trans- and cis-fused 1,5-ditosyl-octahydro-1H-pyrrolo[3,2-c]pyridines, respectively, in good yields via intramolecular aza-Prins cyclization, whereas the coupling of (E)- and (Z)-N-(6-hydroxyhex-3-enyl)-4-methylbenzenesulfonamide afforded the corresponding trans- and cis-fused octahydro-1-tosylpyrano[4,3-b]pyrroles derivatives, respectively, via intramolecular Prins-cyclization.     

ω-Bromoalkapolyenylmethyl ketones-II : Use of 5-bromo-3-penten-2-one ethylene ketal as a c5-synthon

The preparation of the phosphonium salt and the dimethyl-phosphonate of (E)-5-bromo-3-penten-2-one ethylene ketal, 6 and 7, is described. These C₅-isoprenoid synthons were condensed with several aldehydes and ketones giving mixtures of the corresponding E and Z-olefination products. Reaction of the anion of the phosphonate derivative with β-ionone gave 9-cis and 9-trans-β-C₁₈-tetraenone ketals, 13 and 14, which by subsequent hydrolysis afforded 9-cis and 9-tras-β-C₁₈-tetraenones, 15 and 16. A C₈-isoprenoid synthon is also described.     

A model for the complex of the (R)-MTPA ester of trans-4-tert-butylcyclohexanol with Eu(fod)39 based on lanthanide induced shifts

It is shown that the complexation of Eu(fod)₃ with the MTPA ester of trans-4-tert-butylcyclohexanol is very similar to that of ketones with Eu(fod)₃. It is found to be more likely that the MTPA moiety can exist as two rotamers, suggesting that earlier models for correlating LIS and absolute configuration are inadequate.     

Novel polycyclic heterocycles. XII. Reactions of 1,2-dihydro-11-(trifluoromethyl)-3H-7H-quino[8, 1-cd] [1,5]-benzoxazepin-3-one with aromatic aldehydes

The Claisen-Schmidt condensation between 1,2-dihydro-11-(trifluoromethyl)-3H,7H-quino-[8,1 -cd][1,5]benzoxazepin-3-one, 1 , and aromatic aldehydes has been investigated. The acid catalyzed reactions yielded the trans-2-benzylidene derivatives, 4 ; the structures and configurations of the group of compounds represented by 4 have been confirmed by pmr in conjunction with the Eu(fod)₃ shift reagent. In contrast, catalysis with sodium hydroxide gave the isomeric 2-benzyl-endocyclic α,β-unsaturated ketones, 3. Finally, the 4 could be isomerized to the corresponding 3 by means of sodium hydroxide. The ir, uv, and pmr spectra of these compounds are discussed.     

On the geometrical isomers of ethyl 2-cyano-3-ethoxyacrylate

The geometrical configuration of ethyl 2-cyano-3-ethoxyacrylate, 1, has been determined from NMR studies using the chemical-shift reagent Eu(fod)₃-d₂₇     

The stereoselective synthesis of (E)-octafluoro-1,3,5-hexatriene and (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene

(E)-(1,2-Difluoro-1,2-ethenediyl)bis[tributylstannane], 3, readily undergoes a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction with iodotrifluoroethene to yield (E)-octafluoro-1,3,5-hexatriene, 4, in high isomeric purity. (1Z,3E,5Z)-(1,2,3,4,5,6-Hexafluoro-1,3,5-hexenetriyl)bis[tributylstannane], 7, was sequentially prepared from (1Z,3E,5Z)-(1,2,3,4,5,6-hexafluoro-1,3,5-hexenetriyl)bis[triethylsilane], 5, which was prepared via a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction of 3 with (E)-1,2-difluoro-1-iodo-2-triethylsilylethene, 6. Pd(PPh₃)₄/CuI cross-coupling of 7 with iodotrifluoroethene gave (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene, 8.     

Highly stereoselective aziridine ring-opening with phenylselenide anion and selective intramolecular aldol closure for the enantiopure synthesis of γ-aminocyclopentene derivatives

A practical and enantiopure synthesis for the preparation of key intermediates of conformationally locked γ-amino acid and nucleoside analogues is described. First, a highly stereoselective aziridine ring-opening reaction with phenylselenide anion was employed for the stereoselective synthesis of the chiral aminoselenide (1S,2S,1′S)-8, which after N-benzylation was transformed into the corresponding allyl amine (1S,1′S)-7 by oxidation with H₂O₂. Then, dihydroxylation–dehomologation of (1S,1′S)-7 with (OsO₄/NMO, NaIO₄) selectively afforded the desired γ-aminocyclopentene aldehyde (S)-1 and its corresponding γ-amino acid (S)-2 via an intramolecular selective aldol-condensation catalyzed by an internal base.     

Synthesis, properties and structures of the two “electron rich” cobalt-sulphur clusters [Co6(μ3-S)8(PEt3)6]

The reaction of hydrogen sulphide with [Co(H₂O)₆](BF₄)₂ and triethylphosphine in the presence of sodium tetraphenylborate or tetrabutylammonium hexafluorophosphate gave the paramagnetic clusters [Co₆(μ₃-S)₈(PEt₃)₆](Y) (Y = BPh₄, (1), PF₆, (2)). These compounds can be easily reduced by sodium napthalenide to the diamagnetic species [Co₆(μ₃-S)₈(PEt₃)₆] · 2C₄H₈O (3). The molecular structures of 1 and 3 have been established by single-crystal X-ray diffraction methods. Crystal data: (1) space group P , a = 19.481(9), b = 15.562(7), c = 12.390(b) Å, α = 92.70(8), β = 94.50(7), γ = 94.10(9)°, Z = 2, (3) space group R , a = 11.780(6) Å, α = 92.50(7)°, Z = 1. Both structures were solved by the heavy atom method and refined by full-matrix least-squares techniques to the conventional R factors values of 0.050 for 1 and 0.044 for 3 on the basis of 4251 and 1918 observed reflections, respectively. The two clusters [Co₆(μ₃-S)₈)(PEt₃)₆]^1+,0 are isostructural, the inner core consisting of an octahedron of cobalt atoms with all the faces symmetrically capped by triply bridging sulphur atoms. Each metal centre is additionally linked to a triethylphosphine group so that each cobalt atom is co-ordinated by four sulphur atoms and one phosphorus in a distorted square pyramidal environment. The addition of one electron whilst leaving unchanged the geometry of the inner framework, induces small changes in the structural parameters, the average Co---Co and Co---P distances being 2.794 (3) and 2.162 (2) Å for 1 and 2.817 (3) and 2.138 (2) Å for 3 respectively. Electrochemistry in non-aqueous solvents shows the electron-transfer sequence

Full-size image (3K)

The tricationic species is stable only in the short time of cyclic voltammetric tests.     

Eu(fod)3 binding on the 1H‐NMR spectra of bis(2′‐ethylbenzoate)ethylene glycol podands

The complexing and selective binding constants of Eu(fod)₃ with bis(2′‐ethylbenzoate)ethylene glycol podands having one to four oxyethylene groups was observed on their ¹H‐NMR spectra at 250 MHz and 295 K in CDCl₃. The Eu(fod)₃ interaction displayed the selective binding role of oxygen on H₂C–O–CH₂ backbones with referring the ¹H chemical shifts. The estimated equilibrium constants, K_a, of 1:1 ratio of interactions were in accordance with the Eu(fod)₃ ionic radii to bind the oxygen sites depending on the size and conformation of the esters. Esters having one or two ethyleneoxy groups gave mainly 2:2 complexes using ester sites. The minimum lanthanide‐podand ester distance displayed the maximum stability so that ester with four oxyethylene groups was found to bind the Eu(fod)₃ moderately, whereas ester with three oxyethylene groups showed a large induced chemical shift due to the stability of Eu³⁺ complexes with larger ethyleneoxy groups. Copyright © 2012 John Wiley & Sons, Ltd.     

Détermination des configurations Z et E d'imines par RMP. Combinaison de l'étude directe et en présence d'Eu(fod)3

Analysis of NMR spectra of different cyclic and acyclic imines, together with those obtained with the lanthanide shift reagent Eu(fod)₃, allowed the characterisation of the syn-anti (Z-E) isomerism of these compounds. In one case, it was possible to demonstrate a syn-anti equilibration by adding Eu(fod)₃.     

Application of chiral tetrahydropentalene ligands in rhodium-catalyzed 1,4-addition of (E)-2-phenylethenyl- and (Z)-propenylboronic acids to enones

Chiral tetrahydropentalenes (3aR,6aR)-1 have been prepared and used as ligands in the Rh-catalyzed 1,4-addition of 1-alkenylboronic acids to cyclic enones 5. It has been discovered that the stereochemistry of the reaction was controlled by the steric properties of the aryl groups in 1 rather than their electronic nature. In the vinylation with (E)-2-phenylethenylboronic acid 5, ligands (3aR,6aR)-1 provided enantioselectivity up to 87% ee and gave high yields of ethenylketones 6 in the presence of 1 (6.6 mol %). The configuration of all ketone products obtained with (3aR,6aR)-1 is (S). Rh-catalyzed reaction of cyclopentenone 4a and (Z)-propenylboronic acid 7 in the presence of ligands (3aR,6aR)-1 yielded at 50 °C an inseparable mixture of (Z)- and (E)-ketones 8 with (Z)-8 as the major product and both in only moderate enantiomeric excess.     

Intramolecular allylation of the azo group of 2-(allylsilyl)azobenzenes and its photocontrol

Pentacoordinate allylsilanes bearing an azobenzene moiety were synthesized and their structures were elucidated. The reaction of allyldifluorosilane (E)-7a with BF₃ · OEt₂ did not proceed, but (E)-7a was allowed to react with a fluoride ion to give tetrafluorosilicate 8a via intramolecular allyl-migration from the silicon atom onto the azo group. Activation of both the nucleophilic and electrophilic parts by the Si⋯N interaction was found to be important for promotion of the allyl-migration reaction. The azobenzene moiety of the allylsilane was reversibly isomerized by photoirradiation. The (Z)-7a formed by photoirradiation of (E)-7a is in a tetracoordinate state in contrast to the (E)-7a, and it did not react with a fluoride ion at all under the conditions where (E)-7a reacted quantitatively. The reactivity was successfully controlled without changing any conditions other than the change of the coordination number of the silicon atom induced by photoirradiation.     

Reactions of [LiC(SiMe2H)3]·2THF: Sterically hindered tris(dimethylsilyl)methane derivatives and their hydrosilylation

Treatment of LiC(SiMe₂H)₃]·2THF (1) with alkeny1chlorosilanes produced sterically hindered alkenylsilanes (4–10) of structure H₂C=CH---(CH₂)_nSiRR′C(SiMe₂H)₃ (R=Me; R′=Me or Cl; n=0, 1, or 4). The Peterson reaction of 1 with carbonyl compounds gave sterically hindered olefins R(R′)C=C(SiMe₂H)₂. Pt or Rh catalyzed intramolecular hydrosilylation of H₂C=CHSiMe₂C(SiMe₂H)₃ (4) occurred to produce a new 1,3-disilacyclobutane derivative 15. Intermolecular hydrosilylation was favored for 5, 8, and 10, producing oligomeric products.     

Substituted pyridine coordinated N,N-trans and N,N-cis cyclopalladated complexes of (S)-4-tert-butyl-2-phenyl-2-oxazoline: Crystal structures, spectral study and catalysis of the decomposition of PS pesticides

Three pyridine coordinated cyclopalladated complexes: (S)-chloro{2-[2-(4-tert-butyl)oxazolinyl]phenyl-C,N}(4-R-pyridine)palladium(II) (R = H, 2; R = CF₃, 3; R = NMe₂, 4), have been synthesized and structurally characterized. While the crystal structure shows that 2 has a normal N,N-trans-conformation in the coordination sphere of palladium(II), 3 and 4 exhibit uncommon N,N-cis-conformations. From ¹H NMR measurements, the major coordination isomer in deuterated chloroform solution is N,N-trans configuration for three palladacycles. It was found that the three complexes catalyze effectively the methanolysis of the PS pesticides including chiral thiophosphates but show different activity depending on the substituents of co-coordinated pyridine ring in 2–4.     

The influence of excitation of the 4f-orbital of Eu(fod)3 on complex formation with adamantanone and anomalous enhancement of Eu3+ luminescence under the action of H2O and D2O molecules in toluene

The influence of excitation of the 4f-orbital of, β-diketonate Eu(fod)₃ (fod is heptafluorodimethyloctanedione) on the formation of the coordination bond with adamantanone (1) was studied by the nonradiative energy transfer technique. The kinetic parameters of fluorescence (FL) and the lifetime (τ) of the Eu³⁺ ion in toluene solutions were studied. The increase in the stability of the Eu(fod)₃·1 complex when f—f-transitions of the Eu³⁺ ion are excited is related to an increase in the acceptor capability of Eu(fod)₃ due to the increasing fraction of the covalent component determined by the participation of 4f-orbitals. An unexpected effect of enhancement of the Eu(fod)₃ fluorescence under the action of H₂O (D₂O) molecules in toluene solutions was observed. The effect is assumed to be caused by an increase in the negative inductive effect when outer-sphere associates with the fluorinated radical of β-diketonate are formed. The mechanisms of the influence of electron-donating inner-sphere ligands and outer-sphere associates on the quantum yield of fluorescence of Eu(fod)₃ are discussed.     

Synthesis of (3′R,5′S)-3′-hydroxycotinine using 1,3-dipolar cycloaddition of a nitrone

To synthesize (3′R,5′S)-3′-hydroxycotinine [(+)-1], the main metabolite of nicotine (2), cycloaddition of C-(3-pyridyl)nitrones 3a, 3c, and 15 with (2R)- and (2S)-N-(acryloyl)bornane-10,2-sultam [(2R)- and (2S)-8] was examined. Among them, l-gulose-derived nitrone 15 underwent stereoselective cycloaddition with (2S)-8 to afford cycloadduct 16, which was elaborated to (+)-1.     

(C6H16N2)Zn3(HPO3)4H2O: a new layered zinc phosphite templated by diprotonated trans-1,4-diaminocyclohexane

Employing trans-1,4-diaminocyclohexane (trans-1,4-DACH) as a template, a new two-dimensional layered zinc phosphite (C₆H₁₆N₂)Zn₃(HPO₃)₄H₂O (1) has been prepared hydrothermally. Single-crystal X-ray diffraction analysis shows that it crystallizes in the monoclinic space group P2₁/n with a=10.458(2) Å, b=14.720(3) Å, c=13.079(3) Å, β=97.93(3)°, V=1994.1(7) ų, Z=4, R₁=0.0349 (I>2σ(I)) and wR₂=0.0605 (all data). The inorganic layer is built up by alternation of ZnO₄ tetrahedra and HPO₃ pseudo pyramids forming a 4.6.8-net. The sheet is featured by a series of capped six-membered rings. The diprotonated trans-1,4-DACH molecules reside in the interlayer region and interact with the inorganic network through H-bonds.     

Mechanically induced chemiluminescence in the dispiro(adamantane-1,2-dioxetane)—Eu(fod)3 system

Luminescence accompanying an impact mechanical treatment of solid particles of the complex of Eu(fod)₃ (fod is 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione) with dispiro(adamantane-1,2-dioxetane) (1) was discovered and studied. The luminescence has a complex structure, and its spectrum belongs to the excited Eu^III ions. The emission of light is observed only in a mechanical mixture of the Eu(fod)₃ with dioxetane1 and in their cocrystallized form, but not in the case of the components taken separately. The mechanism by which the impacts cause the luminescence is considered. It was shown that the luminescence is not triboluminescence, but is chemiluminescence induced by the decomposition of compound1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1159–1162, May, 1996.     

Etudes d'Alkylidènehydrazono-2 Méthyl-3 Dihydro-2,3 Benzothiazoles par RMN 1H en Présence d'Eu(fod)3

The study of the ¹H n.m.r. spectra of a series of 2-alkylidenehydrazono-3-methyl-2,3-dihydrobenzothiazoles in the presence of Eu(fod)₃ shows that the site of coordination of the lanthanide complex at the two nitrogen atoms of these azines varies as a function of either steric or polar factors. The use of Eu(fod)₃ also makes it possible to determine the Z or E configuration of these compounds, as well as their isomer ratio in different solvents.