The NMR spectra and conformations of dihydropyran derivatives—I: The conformations of 2-alkoxy-5,6-dihydro-α-pyran-6-carboxylic esters

On the basis of NMR spectra of trans- and cis-2-alkoxy-5,6-α-pyran-6-carboxylic esters it was found that, at room temperature, the trans-compounds exist exclusively in the conformation with equatorial carbalkoxy and pseudoaxial alkoxy groups. The cis-isomers appear to be in conformational equilibrium between a form with equatorial carbalkoxy and pseudoequatorial alkoxy groups and that with axial and pseudoaxial substituents. In the latter case, the axial carbalkoxy group is bent out off its normal position by about 15°.     

Complete 1H and 13C NMR spectral assignment of cis- and trans- 3-(2-[2-(4-methylphenyl)ethenyl]phenyl])sydnones

1H and 13C NMR spectra of cis- and trans-3-(2-[2-(4-methylphenyl)ethenyl]phenyl])sydnones, the first stilbene-substituted mezoionic oxadiazolium rings, were fully assigned combining the information in various solvents, such as deuterated benzene, acetone and chloroform, using 2D NMR techniques.     

Nuclear magnetic resonance spectra of psychotherapeutic agents. V*—conformational analysis of 1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-ones

The conformational analysis of biologically active lofendazam (7-chloro-5-phenyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one) is carried out by means of lanthanide shift reagent assisted ¹H NMR spectroscopy: the lanthanide induced shift computer simulation suggests that in deuteriochloroform the heterocyclic ring of lofendazam assumes a cycloheptene-like chair conformation, where 1-N moves away from trigonal stereochemistry to a very flattened pyramidal structure. At room temperature the conformational equilibrium is markedly shifted (85%) towards the conformer showing pseudoaxial H-1 and 5-Ph. The remarkable influence of steric requirements in controlling conformation, and the importance of 3- and/or 4-methyl groups in hindering the ring inversion at room temperature, have been verified by conformational analysis of suitable analogous 1,3,4,5-tetraydro-2H-1,5-benzodiazepin-2-ones.     

Conformational analysis and stereoelectronic effects in trans-1,2-dihalocyclohexanes: 1H NMR and theoretical investigation

The conformational equilibrium of trans-1,2-difluoro- (1), trans-1,2-dichloro- (2) and trans-1,2-dibromo-cyclohexane (3) was studied through a combined method of NMR, theoretical calculations and solvation theory. The solvent dependence of the 3JH1,H2 NMR coupling constants together with theoretical calculations allow the direct determination of the conformational equilibria without recourse to model compounds. The coupling constants were obtained with the aid of spectrum simulation, since these symmetric molecules present complex coupling systems. The observed couplings, when analysed by solvation theory and utilising DFT geometries (B3LYP/6-311+G**), gave energy values of E(ee) -E(aa) of 0.10, 0.95 and 1.40 kcalmol(-1) in the vapour phase for 1, 2 and 3, respectively, decreasing to -0.63, 0.36 and 0.93 kcalmol(-1) in CCl4 and to -1.91, -0.80 and -0.05 kcalmol(-1) in DMSO solution. The diaxial preference for all compounds is explained by natural bond orbital (NBO) analysis, which shows important hyperconjugative effects in this conformation. The "gauche effect" for compounds with more electronegative substituents, which are in gauche arrangement in the ee conformation, also plays a relevant role in more polar solvents.     

Synthesis and structural and photoswitchable properties of novel chiral host molecules: axis chiral 2,2'-dihydroxy-1,1'-binaphthyl-appended stiff-stilbene

Novel photoswitchable chiral hosts having an axis chiral 2,2'-dihydroxy-1,1'-binaphthyl (BINOL)-appended stiff-stilbene, trans-(R,R)- and -(S,S)-1, were synthesized by palladium-catalyzed Suzuki-Miyaura coupling and low-valence titanium-catalyzed McMurry coupling as key steps, and they were fully characterized by various NMR spectral techniques. The enantiomers of trans-1 showed almost complete mirror images in the CD spectra, where two split Cotton effects (exciton coupling) were observed in the beta-transitions of the naphthyl chromophore at 222 and 235 nm, but no Cotton effect was observed in the stiff-stilbene chromophore at 365 nm. The structures of (R)-10 and trans-(R,R)-1 were confirmed by X-ray structural analysis. The optimized structure of cis-1 by MO calculations has a wide chiral cavity of 7-8 A in diameter, whereas trans-1 cannot form an intramolecular cavity based on the X-ray data. Irradiation of (R,R)-trans-1 with black light (lambda = 365 nm) in CH3CN or benzene at 23 degrees C led to the conversion to the corresponding cis-isomer, as was monitored by 1H NMR, UV-vis, and CD spectra. At the photostationary state, the cis-1/trans-1 ratio was 86/14 in benzene or 75/25 in CH3CN. On the other hand, irradiation of the cis-1/trans-1 (75/25) mixture in CH3CN with an ultra-high-pressure Hg lamp at 23 degrees C (lambda = 410 nm) led to the photostationary state, where the cis-1/trans-1 ratio was estimated to be 9/91 on the basis of the 1H NMR spectra. The cis-trans and trans-cis interconversions could be repeated 10 times without decomposition of the C=C double bond. Thus, a new type of photoswitchable molecule has been developed, and trans-1 and cis-1 were quite durable under irradiation conditions. The guest binding properties of the BINOL moieties of trans- and cis-(R,R)-1 with F-, Cl-, and H2PO4- were examined by 1H NMR titration in CDCl3. Similar interaction with F- and Cl- was observed in trans-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (4.6 +/- 0.72) x 102 M-1 for Cl-) and cis-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (5.9 +/- 0.69) x 10 M-1 for Cl-), but H2PO4- interacted differently: the cis-isomer formed the 1/1 complex (Kassoc = (9.38 +/- 2.67) x 10 M-1), whereas multistep equilibrium was expected for the trans-isomer.     

1H (1-D and 2-D) NMR spectra and the conformational states of some 3-monosubstituted saturated five-membered heterocycles

We have recorded the¹H (1-D and 2-D) NMR spectra of sulfolane, a series of 3-monosubstituted sulfolanes, and 3-acetoxy-1,1-diphenylsilacyclopentane. We have determined the chemical shifts and the proton-proton spin-spin coupling constants of seven ring protons. From analysis of the magnitudes of the vicinal spin-spin coupling constants and consideration of the full-cycle pseudorotation model for five-membered heterocycles, we found that seven conformers are most probable for 3-iodo- and 3-tert-butylsulfolanes. Four of these conformers have the half-chair conformation, three have the envelope conformation with pseudoequatorial substituents. The rest of the 3-monosubstituted sulfolanes (chloro-, bromo-, hydroxy-, and methacryloxysulfolanes) and 3-acetoxy-1,1-diphenylsilacyclopentane also have seven preferred conformations, but with pseudoaxial substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2035–2040, September, 1991.     

线型1,2-邻二萘醌-1-肟(1-nqo)钌配合物的合成

报道了含C_(16)长碳链线型1,2-邻二萘醌-1-肟(1-nqo)钌配合物trans-，cis- 及cis-，cis-[Ru(1-nqo)_2(CO)(spy)] (3)及(4)含C_(18)长碳链线型1-nqo钌配合 物cis-，cis-[Ru(1-nqo)_2(CO)(opy)] (5)，trans-，trans-[Ru(1-nqo)_2(opy) _2] (6)的合成。利用红外、FAB质谱、核磁共振氢谱及紫外-可见吸收光谱表征配 合物的结构，利用~1H-~1H偶合二维核磁技术对核磁共振峰进行指认。     

The relevant effect of an intramolecular hydrogen bond on the conformational equilibrium of cis-3-methoxycyclohexanol compared to trans-3-methoxycyclohexanol and cis-1,3-dimethoxycyclohexane

1H NMR data show that an increase in the concentration of cis-3-methoxycyclohexanol (cis-3-MCH) shifts the conformational equilibrium from the 1aa conformer, stabilized by an intramolecular hydrogen bond (IAHB), to the 1ee conformer [X(ee) = 44% (at 0.05 molL(-1)) to 59% (at 0.40 molL(-1)), in CCl4], which forms intermolecular hydrogen bonds (IEHB), as confirmed by IR data. The percentage of 1ee conformer increases with the solvent polarity, from 33% (DeltaG(ee-aa) = 1.72 kJmol(-1)) in cyclohexane (C6D12) to 97% (DeltaG(ee-aa) = -8.41 kJmol(-1)) in DMSO. For trans-3-methoxycyclohexanol (trans-3-MCH), 1ae and 1ea conformers are almost equally present in the studied solvents, 1ae increasing from 41%, in C6D12 (DeltaG(ae-ea) = 0.84 kJmol(-1)), to 49%, in DMSO (DeltaG(ae-ea) = 0.13 kJmol(-1)). A value of 18.4 kJmol(-1) for the strength of IAHB in cis-3-MCH was obtained, from the theoretical data, through the CBS-4M method.     

1H and 13C NMR studies on 1,3,2-dioxarsolanes

The ¹H and ¹³C NMR spectra of a series of 1,3,2-dioxarsolanes have been obtained at 2.1 T and some at 9.4 T. The chemical shifts and spin-spin coupling constants have been obtained from complete spectral analyses of the ¹H and proton-coupled ¹³C spectra. The spectral data are interpreted on the basis of two rapidly interconverting half-chair conformers with a pseudoaxial substituent at arsenic. Unique assignment of syn/anti or cis/trans geometries have been made from ¹H or ¹³C NMR spectroscopy alone. The syn and trans isomers of the 4-methyl- and 4,5-dimethyl-1,3,2-dioxarsolanes, respectively, appear to be conformationally biased towards the forms with pseudoequatorial methyl groups. The general trends in the geminal and vicinal ¹H? ¹H and ¹³C? ¹H coupling constants are interpreted in terms of stereospecific, electronegativity and lone-pair effects of the oxygen heteroatoms and conformational factors. The NMR data on the 1,3,2-dioxarsolanes are discussed with reference to related 1,3-dithoxa- and 1,3-dithia- five-membered rings with As, P, S or C at the 2-position.     

1H NMR Investigation of Si-alkylsubstituted 1,3,5-Trisilacyclohexanes

Alkylsubstituted derivatives of 1,3,5-trisilacyclohexane have been prepared and their ¹H NMR spectra recorded and analyzed. For the compound series 1-mono-, cis-1,3-di- and cis-cis-1,3,5-tri-alkylated derivatives (alkyl = Me, Et, i-Pr and t-Bu) it is found that the conformational preference for an equatorial position of the substituents in the chair form is considerably less than for cyclohexane derivatives. In the compound series trans-1,3-di- and cis-trans-1,3,5-tri-alkylated derivatives the t-butyl group is found to behave uniqually by forcing the ring to escape into the twist-boat form. Each kind of substituent is found to have a characteristic effect on the chemical shift values of the ring protons.     

Structure and intramolecular flexibility of beta-cyclodextrin complex with (-)-epigallocatechin gallate in aqueous solvent

The probable structure of the inclusion complex of beta-cyclodextrin (beta-CD) and (-)-epigallocatechin gallate (EGCg) in D2O was investigated using several NMR techniques. EGCg formed a 1:1 complex with beta-CD, in which the A ring and a portion of the C ring of EGCg were included at the head of the phenolic hydroxyl group attached to C7 of EGCg in the beta-CD cavity from the wide secondary hydroxyl group side. In the 1:1 complex with beta-CD, EGCg maintained the conformation in which the B and B' rings of EGCg took pseudoequatorial and pseudoaxial positions with respect to the C ring, respectively. The structure of the inclusion complexes of beta-CD and EGCg obtained from NMR experiments supported those determined from AM1 semiempirical SCF MO calculations well.     

含手性膦配体的钯（Ⅱ）配合物的二维核磁共振研究

利用一维和二维ＮＭＲ技术，对含有手性膦配体甲基－３脱氧－３（二苯膦基）－４，６－氧－苄叉基－α－Ｄ一吡喃阿卓糖苷（３－ＭＢＰＡ）和甲基－２－脱氧－２－（二苯膦基）－４，６－氧－苄叉基－α－Ｄ－吡喃阿卓糖苷（２－ＭＢＰＡ）的钯配合物ｔｒａｎｓ—［Ｐｄ（３－ＭＢＰＡＨ）２ＣＩ２」（１），ｔｒａｎｓ－［Ｐｄ（２－ＭＢＰＡＨ）２ＣＩ２］（２）和ｃｉｓ－［Ｐｄ（３－ＭＢＰＡ）２］（３），ｃｉｓ－［Ｐｄ（２－ＭＢＰＡ）２］（４）进行~１Ｈ和~（１３）Ｃ ＮＭＲ谱分析，归属了全部的~１Ｈ和~（１３）Ｃ ＮＭＲ谱线，并根据磷的化学位移及Ｒａｍａｎ谱确定化合物（３）和（４）是顺式构型，对实验中的一些现象也做了简单讨论。     

Étude par spectroscopie infrarouge de la conformation de quelques composés contenant le groupement —ochro—(région 2800–3000 cm−1

The specific effect of oxygen lone pairs on the trans CH vibrator, previously noted in dimethyl ether, has been observed in 1,3-dioxolane(D₅) and 1,3-dioxane(D₇). This interaction allows us to determine the conformation of some other compounds with the —OCHRO— group. In 2-methyl and 2-trichloromethyl-1,3-dioxolane, the R group is in an essentially pseudoequatorial position; in 2-ethynyl-1,3-dioxolane, an equilibrium between the two isomers is observed, the isomer with the pseudoaxial R group is more favored in solvent CCl₄ than in solvent CD₃CN. In dimethoxymethane, the gauche—gauche isomer predominates; although other forms appear in 1,1-dimethoxyethane the gauche—gauche isomer is still preferred. In trimethoxymethane, the existence of the two isomers TGG and TGG' has been confirmed. These results complete those previously obtained, essentially from the analysis of NMR spectra of the non-deuterated compounds.     

Photoinduced conformational switch of enantiopure azobenzenes controlled by a sulfoxide

Two series of enantiopure azobenzenes with a p-tolylsulfoxide at the ortho or meta position with respect to the azo group, have been regioselectively synthesized. Both can act as enantiopure molecular switches showing different structural features owing to the presence of the stereogenic sulfur. The photoisomerization process, studied by UV-vis, circular dichroism (CD), NMR, and chiral HPLC evidenced a double role of the sulfoxide. A transfer of chirality from the sulfoxide to the azo system was observed by CD in both cis and trans-isomers of the meta sulfinyl derivatives 3, whereas this perturbation was evident for the ortho sulfinyl series 7 only in the cis isomer. The NMR study evidenced that the s-cis rigid conformation of the bisaromatic sulfoxide was fixing a different orientation of the overall system in each series both in the trans and cis isomers, by forcing a final U-shaped structure in cis-3 and an S-shaped structure in cis-7. Very different values of specific optical rotations were measured in both trans and cis isomers, also reflecting the existence of distinct chiral entities in the photostationary states. The easy and reversible changes occurring between different conformational states could find applications in the photocontrol of several molecular switches.     

Bis(acetylacetonato)ruthenium(II) complexes containing alkynyldiphenylphosphines. Formation and redox behaviour of [Ru(acac)2(Ph2PC triple bond CR)2] (R=H, Me, Ph) complexes and the binuclear complex cis-[{Ru(acac)2}2(micro-Ph2PC triple bond CPPh2)}2

Two equivalents of Ph(2)PC triple bond CR (R=H, Me, Ph) react with thf solutions of cis-[Ru(acac)(2)(eta(2)-alkene)(2)] (acac=acetylacetonato; alkene=C(2)H(4), 1; C(8)H(14), 2) at room temperature to yield the orange, air-stable compounds trans-[Ru(acac)(2)(Ph(2)PC triple bond CR)(2)] (R=H, trans-3; Me=trans-4; Ph, trans-5) in isolated yields of 60-98%. In refluxing chlorobenzene, trans-4 and trans-5 are converted into the yellow, air-stable compounds cis-[Ru(acac)(2)(Ph(2)PC triple bond CR)(2)] (R=Me, cis-4; Ph, cis-5), isolated in yields of ca. 65%. From the reaction of two equivalents of Ph(2)PC triple bond CPPh(2) with a thf solution of 2 an almost insoluble orange solid is formed, which is believed to be trans-[Ru(acac)(2)(micro-Ph(2)PC triple bond CPPh(2))](n) (trans-6). In refluxing chlorobenzene, the latter forms the air-stable, yellow, binuclear compound cis-[{Ru(acac)(2)(micro-Ph(2)PC triple bond CPPh(2))}(2)] (cis-6). Electrochemical studies indicate that cis-4 and cis-5 are harder to oxidise by ca. 300 mV than the corresponding trans-isomers and harder to oxidise by 80-120 mV than cis-[Ru(acac)(2)L(2)] (L=PPh(3), PPh(2)Me). Electrochemical studies of cis-6 show two reversible Ru(II/III) oxidation processes separated by 300 mV, the estimated comproportionation constant (K(c)) for the equilibrium cis-6(2+) + cis6 <=> 2(cis-6(+)) being ca. 10(5). However, UV-Vis spectra of cis-6(+) and cis-6(2+), generated electrochemically at -50 degrees C, indicate that cis-6(+) is a Robin-Day Class II mixed-valence system. Addition of one equivalent of AgPF(6) to trans-3 and trans-4 forms the green air-stable complexes trans-3 x PF(6) and trans-4 x PF(6), respectively, almost quantitatively. The structures of trans-4, cis-4, trans-4 x PF(6) and cis-6 have been confirmed by X-ray crystallography.     

Stereochemical properties of glucosyl sulfoxides in solution

A series of alkyl β-glucosyl sulfoxides were synthesized and characterized in order to study their stereochemical properties. The dependence of the aglycon, solvent and absolute configuration of the sulfinyl group on the conformational properties around the glucosidic and C5-C6 (hydroxymethyl group) bonds were studied. The results for R(S) sulfoxides show linear correlations between the rotamer populations of the hydroxymethyl group and the corresponding Taft's steric parameter (E(S)) of the alkyl group attached to the sulfinyl group in polar and apolar solvents, an increase in the absolute value of E(S) leading to an increase in the gt population. In addition, NOE experiments reveal that as the bulkiness of the alkyl group increases the population of the g- rotamer increases, the latter stabilized by the exo-anomeric effect. These results are in complete agreement with the participation of the exo-anomeric effect in both conformational properties of R(S) sulfoxides. Sulfoxides with the S(S) configuration show different behavior to their R(S) epimers; thus, an increase in the E(S) value of the alkyl group leads to similar or lower gt populations in apolar solvents and to increases in gt in polar solvents. Their NOE studies reveal a conformational equilibrium (in polar and apolar solvents) between g- and g+, dependent on the size of the alkyl group R attached to the sulfinyl group. All these results for both epimers support the general hypothesis that the exo-anomeric effect modifies the conformation of the hydroxymethyl group, fulfills the stereoelectronic requirements, and shows dependence on the solvent.     

NMR-Untersuchungen bei Prolin-enthaltenden Diketopiperazinen

The NMR-spectra of cis- and trans-isomers of proline-containing diketopiperazines were investigated. It was demonstrated that the differences in the spectra are connected to the different position (pseudoaxial or pseudoequatorial) of the substituent (α-hydrogen atom, α-methyl-group, α-isopropyl-group).     

Novel hydridoirida-beta-diketones containing small molecules, CO, or ethylene: their behavior in coordinating solvents such as dimethylsulfoxide or acetonitrile

New hydridoirida-beta-diketones [IrH[(PPh2(o-C6H4CO))2H](CO)]ClO4 2 and [IrH[(PPh2(o-C6H4CO))2H](olefin)]BF4 (olefin = C2H4, 5; 1-hexene, 10) have been prepared. These complexes may afford new diacylhydridoiridium(III) derivatives. In chloroform solution, complex 2 is in equilibrium with the deprotonated diacylhydride trans-[IrH(PPh2(o-C6H4CO))2(CO)] complex 3. In DMSO, deprotonation of 2 occurs to yield the kinetically favored product 3, which isomerizes to the thermodynamically favored complex cis-[IrH(PPh2(o-C6H4CO))2(CO)] 4. Reprotonation of 4 with HBF4 in chlorinated solvents gives the cation in 2. In coordinating solvents such as dimethyl sulfoxide or acetonitrile, complex 5 undergoes displacement of ethylene to afford [IrH{(PPh2(o-C6H4CO))2H](L)]BF4 (L = DMSO, 7; CH3CN, 9). Complexes 5 and 7 undergo deprotonation by NEt3 to give the corresponding diacylhydrides. The ethylene complex gives only trans-[IrH(PPh2(o-C6H4CO))2(C2H4)] 6, while the dimethyl sulfoxide derivative affords a mixture of trans- and cis-[IrH(PPh2(o-C6H4CO))2(DMSO)] 8. Complex 10 shows inhibited alkene rotation around the Ir-olefin axis. All of the complexes were fully characterized spectroscopically. Single-crystal X-ray diffraction analysis was performed on complexes 3, 4, and 9. The 13C NMR and X-ray data point to a carbenoid character in the carbon atoms bonded to iridium in the irida--diketone fragment, so that it can be considered as an acyl(hydroxycarbene) moiety.     

Absence of reverse anomeric effect in furanosides

A series of conformationally restricted N-"furanosides" has been synthesized, where the carbons of the tetrahydrofuran ring are kept in one plane by a rigid norbornane skeleton, permitting only the ring oxygen to move above or below the tetrahydrofuran ring plane. This causes the substituents of the anomeric carbon to occupy a pseudoaxial or a pseudoequatorial position. On protonation of these "norbornane-furanosides" with trifluoromethanesulfonic acid, all three compounds exhibited decreasing coupling constants for the anomeric proton, indicating a shift toward the pseudoaxial conformation. The coupling constant measurements were supported by volume integration of NOESY cross-peaks, which also showed a change toward the pseudoaxial conformation upon protonation of the nitrogen. These results provide no evidence for the so-called reverse anomeric effect; on the contrary they are in full agreement with a small normal anomeric effect.     

Conformational analysis of 2-phenyl-2-oxo-5,6-benzo-1,3,2-dioxaphosphepine with data from vibrational spectroscopy,dipole moments,and the kerr effect

2-Phenyl-2-oxo-5,6-benzo-1,3,2-dioxaphosphepine exists in a melt and solutions in polar solvents as a three-component equilibrium of two chair forms (C) with axial and equatorial arrangement of the phenyl group and the twist-boat form (TB) with a pseudoequatorial position of the phenyl substituent, a-C e-C e-TB. The two-component equilibrium e-C e-TB is observed in nonpolar solvents. The e-TB conformation occurs in the crystalline state. The dipole moment of the P=O groups is 3.5 D. The angle of rotation of the plane of the phenyl group with respect to the P=O bond in the e-TB conformation was 54 or 129.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1039–1043, May, 1991.