NMR-Untersuchungen an Dicyclopentadienderivaten. IV—1-Syn/anti-Epimere von endo-Dicyclopentadienderivaten

The syn/anti-arrangement of some substituents R in position 1 of endo-dicyclopentadiene derivatives is investigated by ¹H-and ¹³C n.m.r. spectroscopy. The HH-coupling constants of the epimeric alcohols 2 and 3 are determined by paramagnetic shift experiments [Eu(fod)₃] and the observed relative paramagnetic shifts ΔEu used for the determination of the configuration. The increasing steric compression in the syn-epimers is well reflected by the ¹H- and ¹³C n.m.r. chemical shifts.     

The adamantane rearrangement of syn- and anti-Tricyclo[4.2.1.1.12,5] decane. Part II. Rearrangements initiated by regioselective formation of carbocations at C(3) and C(9)

The endo- and exo-alcohols 5–12 of syn-( 1 ) and anti-tricyclo[4.2.1. 1^2.5]decane ( 2 ) were treated with BF₃/Et₃SiH (ionic hydrogenation) in order to study the behaviour of the corresponding regioselectively generated carbocations at C(3) ( a (syn), b (anti)) and C(9) ( c (syn), d (anti)). The anti-hydrocarbon 2 is practically the sole product obtained starting with the four 3-alcohols (via a → b from 5 and 6 (syn) and via b from 9 and 10 (anti)). The four 9-alcohols in each case yield a mixture of 2-endo, 3-endo- ( 3 ) and 2-exo,3-exo-trimethylene-8,9,10-trinorbornane (4) (via c → e from 7 and 8 (syn) and via d → f from 11 and 12 (anti)), but no hydrocarbon 2 , i.e. none of the 1,3-H shifts c → a and d → b is involved.     

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.     

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.     

Equilibres conformationnels de glucides au niveau de liaisons σ sp2-sp3 C-C. III Dérivés d'oximes d'aldéhydo-sucres utilisation de tris-dipivaloylméthanato-europium

A series of sugar oximes and O-methyloximes of the general formula RCH?NOR′ (R′ ? H, CH₃) have been studied by PMR. spectroscopy. These compounds exist in solution as a mixture of the syn and anti isomers. The conformational equilibrium of the syn isomers seems to consist exclusively of the eclipsed rotamers, whereas for the anti isomers there appears to be a significant contribution from bisecting rotamers. Using tris-dipivaloylmethanato-europium it is found that the α proton of the anti oximes is much more deshielded than the corresponding proton of the syn isomers, which means that the downfield shift of a particular proton does not depend exclusively on its distance from the oxygen of the oxyimino group.     

A 1H-NMR Spectroscopic Investigation of the Conformation of the Acetamido Group in Some Derivatives of N-Acetyl-D-allosamine and -D-glucosamine

The population of the conformations obtained by rotation around the C(2)? N and the N? C(O) bonds of AllNAc, GlcNAc, and GlcNMeAc derivatives was investigated by ¹H-NMR spectroscopy. The AllNAc-derived α-D -and β-D -pyranosides 4–7 , the AllNAc diazirine 16 , and the GlcNAc-derived axial anomers α-D - 8–10 prefer the (Z)-anti-conformation. A significant population of the (Z)-syn-conformer in the (Z)-syn/(Z)-anti-equilibrium for the equatorial anomers β-D - 8–10 and the GlcNAc diazirine 17 was evidenced by an upfield shift of H? C(2), downfield shifts of H? C(1) and H? C(3), and by NOE measurements. The population of the (Z)-syn-conformation depends on the substituent at C(1) and is highest for the hexafluoroisopropyl glycoside. The population of the (Z)-syn-conformation of β-D - 14 decreases with increasing polarity of the solvent, but a substantial population is still observed for solutions in D₂O. Whereas the α-D -anomers of the hemiacetal 22 and the methyl glycoside 21 prefer the (Z)-anti-conformation in D₂O solution, the corresponding β-D -anomers are mixtures of the (Z)-anti-and (Z)-syn-conformers. The diazirine 17 self-associates in CD₂Cl₂ solution at concentrations above 0.005M at low temperatures. The axial anomers of the GlcNMeAc derivatives α-D - 26–28 are 2:1 to 3:1 mixtures of (Z)-anti-and (E)-anti-conformers, whereas the corresponding β-D -glycosides are ca. 1:3:6 mixtures of (Z)-syn-, (Z)-anti-, and (E)-anti-conformers.     

Hydrazines et hydrazones heterocycliques. III. Synthese de derives du naphto[2,3-d]thiazole

The synthesis of 2-hydrazinonaphtho[2,3-d]thiazole, 3-methylnaphtho-[2,3-d]thiazolin-2-one hydrazone and some of the corresponding 2-alkylidenehydrazino-3-methylnaphtho[2,3-d]thiazoles is described. These compounds have been characterized by their infrared, ultraviolet, nmr spectra in the presence of Eu(fod)₃ and by their mass spectra.     

1,3-Dipolar cycloaddition of α-alkoxycarbonylnitrones with vinyl ethers and allyl alcohols in the presence of Eu(fod)3: selective activation of (Z)-isomers of the nitrones

Uncatalyzed cycloaddition of α-alkoxycarbonylnitrones 1 with vinyl ethers 7 gave mixtures of cis- and trans-cycloadducts 8, whereas Eu(fod)₃-catalyzed cycloaddition of 1 with 7 gave the trans-cycloadducts trans-8 in a highly stereoselective manner. NMR studies indicated that Eu(fod)₃ selectively activated (Z)-nitrones (Z)-1 in E,Z-equilibrium mixtures of nitrones 1. In contrast, the reaction of 1 with allyl alcohols 12 in the presence of Eu(fod)₃ resulted in sequential transesterification and intramolecular cycloaddition to give intramolecular cycloadducts 13.     

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.     

Trisphosphine‐Chelate‐Substituted Molybdenum and Tungsten Nitrosyl Hydrides as Highly Active Catalysts for Olefin Hydrogenations

Reaction of [M(NO)Cl₃(NCMe)₂] (M=Mo, W) with (iPr₂PCH₂CH₂)₂PPh (etpⁱp) at room temperature afforded the syn/anti‐[M(NO)Cl₃(mer‐etpⁱp)] complexes (M=Mo, a ; W, b ; 3 a,b (syn,anti); syn and anti refer to the relative position of Ph(etpⁱp) and NO). Reduction of 3 a,b (syn,anti) produced [M(NO)Cl₂(mer‐etpⁱp)] ( 4 a,b (syn)), [M(NO)Cl(NCMe)(mer‐etpⁱp)] ( 5 a,b (syn,anti)), and [M(NO)Cl(η²‐ethylene)(mer‐etpⁱp)] ( 6 a,b (syn,anti)) complexes. The hydrides [M(NO)H(η²‐ethylene)(mer‐etpⁱp)] ( 7 a,b (syn,anti)) were obtained from 6 a,b (syn,anti) using NaHBEt₃ (75 °C, THF) or LiBH₄ (80 °C, Et₃N), respectively. 7 a,b (syn,anti) were probed in olefin hydrogenations in the absence or presence of a hydrosilane/B(C₆F₅)₃ mixture. The 7 a,b (syn,anti)/Et₃SiH/B(C₆F₅)₃ co‐catalytic systems were highly active in various olefin hydrogenations (60 bar H₂, 140 °C), with maximum TOFs of 5250 h^?1 ( 7 a (syn,anti)) and 8200 h^?1 ( 7 b (syn,anti)) for 1‐hexene hydrogenation. The Et₃SiH/(B(C₆F₅)₃ co‐catalyst is anticipated to generate a [Et₃Si]⁺ cation attaching to the O_NO atom. This facilitates NO bending and accelerates catalysis by providing a vacant site. Inverse DKIE effects were observed for the 7 a (syn,anti)/Et₃SiH/(B(C₆F₅)₃ (k_H/k_D=0.55) and the 7 b (syn,anti)/Et₃SiH/(B(C₆F₅)₃ (k_H/k_D=0.65) co‐catalytic mixtures (20 bar H₂/D₂, 140 °C).     

The Aluminum-Bromide-Catalyzed Adamantane Rearrangement of syn- and anti-Tricyclo[4.2.1.12,5]decane

In the presence of AlBr₃ in CS₂ at temperatures below 0°, syn-tricyclo[4.2.1.1^2,5]decane ( 1 ) isomerizes exclusively to anti-tricyclo[4.2.1.1^2,5]decane ( 2 ) at a higher rate than the latter rearranges to 2-exo,3-exo-trimethylene-8,9,10-trinorbornane ( 4 ). However, at temperature above 0°, the anti-isomer 2 isomerizes to 4 faster than 1 to 2 and 4 . As a consequence, hydride abstraction occurs at C(3) (→carbocation a , which rearranges to carbocation b (anti-skeleton)) in the syn-isomer 1 , and more readily at C(9) (→carbocation c ) than at C(3) (→carbocation b ) in the anti-isomer 2 .     

Excitation Energy-Transfer Processes in the Sensitization Luminescence of Europium in a Highly Luminescent Complex

The excitation energy transfer (EET) pathways in the sensitization luminescence of Eu^III and the excitation energy migration between the different ligands in [Eu(fod)₃dpbt] [where fod=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and dpbt=2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine], exhibiting well-separated fluorescence excitation and phosphorescence bands of the different ligands, were investigated by using time-resolved luminescence spectroscopy for the first time. The data clearly revealed that upon the excitation of dpbt, the sensitization luminescence of Eu^III in [Eu(fod)₃dpbt] was dominated by the singlet EET pathway, whereas the triplet EET pathway involving T₁(dpbt) was inefficient. The energy migration from T₁(dpbt) to T₁(fod) in [Eu(fod)₃dpbt] was not observed. Moreover, upon the excitation of fod, a singlet EET pathway for the sensitization of Eu^III luminescence, including the energy migration from S₁(fod) to S₁(dpbt) was revealed, in addition to the triplet EET pathway involving T₁(fod). Under the excitation of dpbt at 410 nm, [Eu(fod)₃dpbt] exhibited an absolute quantum yield for Eu^III luminescence of 0.59 at 298 K. This work provides a solid and elegant example for the concept that singlet EET pathway could dominate the sensitization luminescence of Eu^III in some complexes.     

Chemistry of thienopyridines. XIX. Further studies on chlorination and S-oxidation in the thieno[2,3-b] pyridine system

Treatment of thieno [2,3-b] pyridine (1a) with chlorine gas in chloroform (plus water) gave a mixture of two 2,3-dichloro-2,3-dihydrothieno[2,3-b] pyridine 1-oxides [trans-syn (IIa), and cis-anti (IIb)) [and 2,3,3-trichloro-2,3-dihydrothieno[2,3-b]pyridine syn-1-oxide (IVa), as well as a non-isolated fourth product (prohably the anti isomer of IVa) and sometimes a small amount of thieno[2,3-b]pyridine 1,1-dioxide (III). Treatment of Ia in a solvent (water, chloroform-water, or THF-water) with sulfuric acid and sodium hypochlorite gave a mixture of IIb and III. Effects of variations of reaction conditions on the composition of the product mixture were ascertained through chemical isolation and/or pmr analysis. Products formed were rationalized in terms of the chlorine-water-hypochlorous acid equilibrium, plus attack of chlorine variously at positions 1 (S-atom), 2, and 3 of 1a, but of hypochlorous acid only at position 1. Thermal and chromatographic limitations on isolation procedures for some of the products were established. Stereochemistries of IIa, IIb, and IVa were assigned by means of pmr spectrometry with the aid of the shift reagent Eu(fod)₃. Spin-spin couplings between the proton at position 2 and those at positions 4 and 6 were observed at high resolution. In exploratory runs, 5-ethyl-la was converted into isolable 2,3-dichloro-5-ethyl-2,3-dihydrothieno[2,3-b]pyridine 1-oxide, and 5-acetyl-Ia yielded 3-chloro-5-acetylthieno] 2,3-b]pyridine. Mass spectral fragmentation patterns for the various products are presented.     

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.     

Adducts of Tricyclo[4.1.0.0<Superscript>2,7</Superscript>]heptane hydrocarbons with methane- and Halomethanesulfonyl Thiocyanates and their transformations in the presence of bases (nucleophiles)

1-R-Tricyclo[4.1.0.0^2,7]heptanes (R = H, Me, Ph) take up methane- and halomethanesulfonyl thiocyanates XCH₂SO₂SCN (X = H, Cl, Br) at the central C¹–C⁷ bond in benzene at 20°C with high anti-selectivity to give bicyclo[3.1.1]heptane derivatives with the 7-endo-oriented sulfonyl group and the thiocyanato group in the geminal position with respect to the R substituent. The syn-adducts lose HSCN molecule by the action of potassium tert-butoxide in THF at 0°C or on heating in boiling aqueous dioxane containing NaOH with formation of 1-(X-methylsulfonyl)tricyclo[4.1.0.0^2,7]heptanes. Under analogous conditions the anti-adducts (X = Me) are converted into 1,2-bis(7-syn-methylsulfonyl-6-endo-R-bicyclo[3.1.1]hept-6-exo-yl)disulfanes. The anti-adduct derived from unsubstituted tricyclo[4.1.0.0^2,7]heptane and MeSO₂SCN reacted with methyllithium or phenylmagnesium bromide to produce 7-anti-methyl(phenyl)sulfanyl-6-endo-methylsulfonylbicyclo-[3.1.1]heptanes which were also obtained by photochemical addition of MeSO₂SMe(or Ph) to tricyclo-[4.1.0.0^2,7]heptane. Geometric parameters of radical intermediates in the sulfonylation of 1-R-tricyclo-[4.1.0.0^2,7]heptanes were optimized ab initio using 6-31G basis set.     

trans–cis Isomerization of schiff's bases (N-benzylideneanilines) on addition of lanthanide shift reagents

Application of the lanthanide shift reagent Eu(fod)₃ to a series of benzylideneanilines causes isomerization of the stable trans form to the less stable cis form. A linear relationship was obtained between the % cis isomer with the mole ratio of Eu(fod)₃/substrate.     

Binuclear trans‐Bis(β‐iminoaryloxy)palladium(II) Complexes Doubly Linked with Pentamethylene Spacers: Structure‐Dependent Flapping Motion and Heterochiral Association Behavior of the Clothespin‐Shaped Molecules

The synthesis, structure, and solution‐state behavior of clothespin‐shaped binuclear trans‐bis(β‐iminoaryloxy)palladium(II) complexes doubly linked with pentamethylene spacers are described. Achiral syn and racemic anti isomers of complexes 1 – 3 were prepared by treating Pd(OAc)₂ with the corresponding N,N′‐bis(β‐hydroxyarylmethylene)‐1,5‐pentanediamine and then subjecting the mixture to chromatographic separation. Optically pure (100 % ee) complexes, (+)‐anti‐ 1 , (+)‐anti‐ 2 , and (+)‐anti‐ 3 , were obtained from the racemic mixture by employing a preparative HPLC system with a chiral column. The trans coordination and clothespin‐shaped structures with syn and anti conformations of these complexes have been unequivocally established by X‐ray diffraction studies. ¹H NMR analysis showed that (±)‐anti‐ 1 , (±)‐anti‐ 2 , syn‐ 2 , and (±)‐anti‐ 3 display a flapping motion by consecutive stacking association/dissociation between cofacial coordination planes in [D₈]toluene, whereas syn‐ 1 and syn‐ 3 are static under the same conditions. The activation parameters for the flapping motion (ΔH^≠ and ΔS^≠) were determined from variable‐temperature NMR analyses as 50.4 kJ mol^?1 and 60.1 J mol^?1 K^?1 for (±)‐anti‐ 1 , 31.0 kJ mol^?1 and ?22.7 J mol^?1 K^?1 for (±)‐anti‐ 2 , 29.6 kJ mol^?1 and ?57.7 J mol^?1 K^?1 for syn‐ 2 , and 35.0 kJ mol^?1 and 0.5 J mol^?1 K^?1 for (±)‐anti‐ 3 , respectively. The molecular structure and kinetic parameters demonstrate that all of the anti complexes flap with a twisting motion in [D₈]toluene, although (±)‐anti‐ 1 bearing dilated Z‐shaped blades moves more dynamically than I‐shaped (±)‐anti‐ 2 or the smaller (±)‐anti‐ 3 . Highly symmetrical syn‐ 2 displays a much more static flapping motion, that is, in a see‐saw‐like manner. In CDCl₃, (±)‐anti‐ 1 exhibits an extraordinary upfield shift of the ¹H NMR signals with increasing concentration, whereas solutions of (+)‐anti‐ 1 and the other syn/anti analogues 2 and 3 exhibit negligible or slight changes in the chemical shifts under the same conditions, which indicates that anti‐ 1 undergoes a specific heterochiral association in the solution state. Equilibrium constants for the dimerizations of (±)‐ and (+)‐anti‐ 1 in CDCl₃ at 293 K were estimated by curve‐fitting analysis of the ¹H NMR chemical shift dependences on concentration as 26 M ^?1 [K_D(racemic)] and 3.2 M ^?1 [K_D(homo)], respectively. The heterochiral association constant [K_D(hetero)] was estimated as 98 M ^?1, based on the relationship K_D(racemic)=1/2 K_D(homo)+1/4 K_D(hetero). An inward stacking motif of interpenetrative dimer association is postulated as the mechanistic rationale for this rare case of heterochiral association.     

Asymmetric Diels-Alder Reaction of 1-Methoxybuta-1,3-diene with (2R)-N-Glyoxyloylbornane-10,2-sultam

Starting from sultam 1 , the chiral dienophile (2R)-N-glyoxyloylbornane-10,2-sultam ( 4 ) was readily prepared. Non-catalyzed atmospheric- and high-pressure as well as [Eu(fod)₃]-promoted [4 + 2] cycloadditions of 1-methoxy-buta-1,3-diene ( 5 ) to chiral dienophile 4 , leading with high asymmetric induction to 6-methoxy-3,6-dihydro-2H-pyran-2-yl derivatives 6 – 9 , are described. The extent and direction of asymmetric induction in these reactions were established by ¹H-NMR analysis and chemical correlation, respectively. Stereochemical models for both non-catalyzed and [Eu(fod)₃]-promoted reactions are proposed.     

NMR–Untersuchungen an Dicyclopentadienderivaten: I—1H-NMR: Anwendung von paramagnetischen Verschiebungsreagenzien (Eu(fod)3) zur Vereinfachung der Spektren exo/endo-isomerer Diole

The determination of the stereochemistry of a series of exo/endo-isomeric dihydro- and tetrahydro-dicyclopentadiene-9.10-diols (exo/exo or endo/endo), using Eu(fod)₃ for separation of the signals in their ¹H n.m.r. spectra, is discussed in detail. The paramagnetic shift values ΔEu determined for half-molar ratios Eu(fod)₃/diol allow an unambiguous stereochemical assignment of the diols with regard to exo/endo isomerism. The ΔEu quantities are correlated with the distance H_i…O-atom (R_i).     

Characterization of di- and trimethoxybenzaldehydes by analysis of deshielding gradients obtained with Eu(fod)3 shift reagent

Eu(fod)₃ shift reagent was used to simplify PMR spectra from isomeric mono-, di and trimethoxybenzaldehydes. Deshielding gradients, obtained by plotting induced shift vs. molar ratio of [Eu(fod)₃]/[substrate] made it possible to assign methoxyl proton signals to the correct positional substituent in polymethoxylated benzaldehydes. Anomalous upfield shifts for the aldehydic protons of 2,6-dimethoxy- and 2,4,6-trimethoxybenzaldehyde were observed with Eu(fod)₃ Various instances of long-range (⁵J) proton coupling between the aldehydic proton and a meta-proton provide insight to the geometry of the substrate in the complexed state with Eu(fod)₃. Di- and trimethoxybenzaldehydes are important precursors for the synthesis of the correspondingly methoxylated amphetamines which are of pharmacological and forensic interest because of abuse and illicit manufacture.