Enantioselective cyclopropanation reaction using a conformationally fixed pyridinium ylide through a cation-π interaction

Using a chiral pyridinium ylide with a fixed conformation through a cation-π interaction performs enantioselective cyclopropanation of electron-deficient olefins. ¹H NMR, X-ray structural analysis and DFT calculations elucidated the self-complexation and the face-to-face arrangement between the pyridinium and the phenyl rings. The absolute configuration of the product was determined after conversion into a bicyclic cyclopropane derivative.     

Some Comments on the Conformations of Methyl Phenyl Sulfides,Sulfoxides and Sulfones

¹³C-NMR. and He (Iα) photoelectron spectra of alkyl phenyl sulfides, sulfoxides and sulfones have been used to probe how their conformations depend on the size of the alkyl groups R. The results are interpreted to indicate that in the sulfides the S, R-bond is twisted out of the planar conformation with increasing size of the alkyl group, whereas in the sulfoxides and sulfones the preferred conformation with the S, R-bond perpendicular to the phenyl group plane seems to be independent of the size of R. These conclusions are in agreement with previous work on the alkyl phenyl sulfides and provide strong support for previous conjectures concerning the preferred conformations of alkyl phenyl sulfoxides and sulfones.     

Synthesis of four new carboxylic derivatives based on the [1.1.1.1]metacyclophane backbone blocked in 1,3-Alternate conformation

Four new tetrasubstituted [1.1.1.1]metacyclophanes (4–7), that are inherently adopting a 1,3-Alternate conformation, bearing four or eight peripheral carboxylic binding sites, and appended with spacers group (alkyl or phenyl) differing by the flexibility, have been synthesised in high yields. The structures of the obtained compounds have been investigated in solution as well as in the solid state, for three of them, by using single-crystal X-ray analysis.     

Structure and conformational analysis of 2-hydroxy-5-isobutyl-1,3,2-dioxaborinane

The structure of 2-hydroxy-5-isobutyl-1,3,2-dioxaborinane, one of the major autooxidation products of 5-isobutyl-2-isopropyl-1,3,2-dioxaborinane, has been studied by ¹H, ¹³C, and ¹¹B NMR spectroscopy together with X-ray analysis. Molecules of the title compounds adopt a sofa conformation with equatorial isobutyl substituent. The ring interconversion path, free conformational energy, and optimal conformation of the isobutyl group (corresponding to the X-ray diffraction data) were determined by DFT quantum chemical calculations at the PBE/3ξ level of theory.     

Conformational study of tetramethyl-N,N′-bis-arylcyclodisilazanes by 13C NMR and x-ray diffraction analysis: III. The conformation of tetramethyl-N,N′-bis(O-methoxyphenyl)cyclodisilazane

The conformation of tetramethyl-N,N′-bis(o-methoxyphenyl)cyclodisilazane was investigated by ¹³C NMR in solution and by X-ray diffraction in the solid state. The conformation in solution compares to that of o-methoxyaniline. The phenyl and the cyclodisilazane ring forms a dihedral angle of 7.4° and there is a non-bonded Si ⋯ O distance of 2.73 Å in the crystal. The molecular geometry suggests an analogy to S ⋯ O non-bonded interactions often observed in organosulphur chemistry.     

Single crystal X-ray diffraction analysis of the structure of methyl 4-methyl-3,5-dioxo-1-phenyl-2-oxaspiro [5.5] undecane-4-carboxylate

A single crystal X-ray diffraction study of the crystals of methyl 4-methyl-3,5-dioxo-1-phenyl-2-oxaspiro[5.5]undecane-⁴-carboxylate shows that phenyl and methoxycarbonyl substituents are in the equatorial position on the one side of the dioxopyran ring with twist boat conformation.     

3D-QSAR study of hallucinogenic phenylalkylamines by using CoMFA approach

The three-dimensional quantitative structure–activity relationship (3D-QSAR) has been studied on 90 hallucinogenic phenylalkylamines by the comparative molecular field analysis (CoMFA). Two conformations were compared during the modeling. Conformation I referred to the amino group close to ring position 6 and conformation II related to the amino group trans to the phenyl ring. Satisfactory results were obtained by using both conformations. There were still differences between the two models. The model based on conformation I got better statistical results than the one about conformation II. And this may suggest that conformation I be preponderant when the hallucinogenic phenylalkylamines interact with the receptor. To further confirm the predictive capability of the CoMFA model, 18 compounds with conformation I were randomly selected as a test set and the remaining ones as training set. The best CoMFA model based on the training set had a cross-validation coefficient q ² of 0.549 at five components and non cross-validation coefficient R ² of 0.835, the standard error of estimation was 0.219. The model showed good predictive ability in the external test with a coefficient R _pre² of 0.611. The CoMFA coefficient contour maps suggested that both steric and electrostatic interactions play an important role. The contributions from the steric and electrostatic fields were 0.450 and 0.550, respectively.     

Benzodiselenagermoles and spirobisbenzodiselenagermoles

Synthesis of benzodiselenagermoles and bisbenzodiselenagermoles was carried out by transmetallation group 4 → group 14 between diselenophenylenezirconocenes and dialkyl-, diaryl- or alkylaryldichlorogermanes, aryltrichlorogermane or germanium tetrachloride. The new compounds were studied by ¹H, ⁷⁷Se NMR and mass spectrometry. In the case of compounds with substituted phenyl groups, double irradiation and 2D NMR experiments were performed to determine the chemical shifts of the two selenium atoms. The crystal structure of a spirobisbenzodiselenagermole has been established by X-ray diffraction analysis.     

Structure and Conformational Analysis of 5,5-Bis(bromomethyl)-2-(4-methoxyphenyl)-1,3-dioxane

The structure of 5,5-bis(bromomethyl)-2-(4-methoxyphenyl)-1,3-dioxane has been studied by ¹H and ¹³C NMR and X-ray diffraction. Molecules of the title compound exist in the chair conformation with equatorial orientation of the methoxyphenyl substituent. The dioxane ring inversion path, free conformational energy, and optimal conformation of the aryl group have been determined by computer simulation in terms of the DFT PBE/3ζ method. The calculation results are consistent with the X-ray diffraction data.     

Crystal structure of a 1∶2∶1 packing complex formed by bis(isothiocyanato) tetrakis(pyridine) nickel(II), triphenylmethane,and metanol

The structure of the [NiPy₄(NCS)₂]·2(C₆H₅)₃CH·CH₃OH (Py is pyridine) packing complex was determined by single crystal X-ray diffraction analysis (KM-4 diffractometer, λMoK_α, graphite monochromator, ω/2? scan mode, θ_max, 2073 reflections, R=0.059). The unit cell is base-centered monoclinic, space group C2/c, a=20.22(1), b=14.256(7), c=18.836(6) Å, β=87.40(4)^°, Z=4C₆₁H₅₆N₆NiOS₂, d_calc=1.239 g/cm³. The structure is of the island type and consists of molecules of three types. In the trans-[NiPy₄(NCS)₂] molecule, the central atom has a distorted octahedral environment and is coordinated by six nitrogen atoms of two isothiocyanate and four pyridine ligands. In contrast to the phase of the complex itself, this molecule acquires a four-lobe propeller conformation, in which the pyridine rings are rotated relative to the equatorial plane by angles of 52.8(3) and 50.1(2)^°. The triphenylmethane molecule has a three-lobe propeller conformation, as in triphenylmethane clathrates with benzene, thiophene, pyrrole, and aniline, but strongly deviates from threefold axis symmetry. The phenyl rings form dihedral angles of 25(3), 40(4), and 19(4)^° with the planes formed by the bonds of the ternary carbon atoms with hydrogen atoms and by the appropriate carbon atom of the phenyl ring. The methanol molecules are located inside the direct channels running along the c axis and are disordered around the inversion centers.     

Synthesis,crystal structure and photoluminescence of 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin

A new coumarin derivative, 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin, was synthesized and characterized by FT-IR, ¹H NMR, element analysis and single crystal X-ray crystallography. The dihedral angle of benzo[5,6]coumarin ring and phenyl group is 36.15°, and the dihedral angle of phenyl group and anthracene skeleton is 89.37°. The UV–vis absorption and photoluminescence of the compound were discussed. The result shown that the compound exhibits high fluorescence quantum yield (Φ_F), large Stokes shift and green emission (508 nm). The molecular structure of the compound was optimized using density functional theory (DFT) at B3LYP/6-31G(d) level, and the HOMO and LUMO levels of the compound were deduced.     

Evidence of Hydrogen Bonding in Stabilizing the Cone Conformation of a Monoalkylated Calix[4]arene. X-ray Structure of 25-[2-(ethoxy-1-p-toluene-sulfonate)phenyl]-26,27,28-trihydroxy calix[4]arene

The synthesis of25-[2-(ethoxy-1-p-toluene-sulfonate)phenyl]-26,27,28-trihydroxy calix[4]arene3 as a byproduct of the preparation of 1,3-dialkylated25,27-di-[2-(ethoxy-1p-toluene-sulfonate)phenyl]-26,28-dihydroxy calix[4]arene 2 is reported. Compound 3 is a monoalkylatedcalix[4]arene in the cone conformation. The X-ray structure of 3 showed that this conformation is stabilized by intramolecular hydrogen bonding.     

Structure ofN S-butyl-N O-phenyl(thiooxamide)

The molecular and crystal structure of N^S-butyl-N^O-phenyl(thiooxamide) (1) has been established by X-ray structural analysis. The thiooxamide fragment and the phenyl ring are coplanar. The conformation of 1 is stabilized by NH...O and NH...S hydrogen bonds. No conjugation between the thioamide and the oxamide fragments of the molecule occurs. In the crystal, the centrosymmetrically related molecules 1 are linked in dimers through NH ... O' intermolecular hydrogen bonds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 485–487, February, 1996     

Organosulphur compounds-XXXVIII Axial preference of a 2-dimethoxyphosphoryl substituent in 1,3,5-trithiane

¹H-NMR studies and X-ray analysis indicate that 2-dimethoxyphosphoryl-1,3,5-trithiane exists both in solution and in the crystal in a chair conformation with the dimethoxyphosphoryl group at C-2 being axial.     

Structural and stereochemical nonrigidity of 7-(heptaphenylcycloheptatrienyl) isothiocyanate

By means of DFT B3LYP/6-31G(d, p) calculations of 7-(heptaphenylcycloheptatrienyl) isothiocyanate, the dissociation–recombination mechanism for intramolecular migrations of the isothiocyanato group has been revealed, and the structure of the transition state preceding the formation of a tight ion pair has been found for the first time. According to calculations, the high activation barrier for displacements of the isothiocyanato group ΔE_ZPE^≠ = 21.3 kcal/mol is related to the stable conformation of the molecule with the equatorial–NCS group and the orthogonally located phenyl substituent in the axial position. The rearrangement of the molecule to the form favorable for migrations of the–NCS group involves the inversion of the seven-membered ring accompanied by rotation of the phenyl group.     

Chirality and conformational changes in 4-phenylphenanthrenes and 1-phenylbenzo[c]phenanthrene derivatives

NMR data of several 4-phenylphenanthrenes (15, 16) have revealed that the crowding in these compounds does not lead to chirality at temperatures as low as ?90°. The easy rotation of the phenyl substituent observed by NMR implies that notwithstanding the phenanthrene moiety in average behaves as a planar part the phenyl group does not experience steric hindrance.The analysis of temperature-dependent NMR spectra of several derivatives of 1-phenylbenzo[c]phenanthrenes (17-20) indicated that in these compounds exchange processes do occur. By calculations of the free energies of activation from the NMR data two processes could be distinguished: rotation of the phenyl substituent at one side of the helical benzo[c]phenanthrene moiety, for which ΔG^XXX_rot , is ca. 13.0$\text{kcal}\text{mol}$ or slightly larger when bulky substituents are present at C₂, and racemisation by a rotation of the phenyl group around the opposite end of the benzo[c]phenanthrene skeleton with simultaneous inversion of the helical conformation. For this process ΔG^XXX_rac is ca. 16$\text{kcal}\text{mol}$. The results have been compared with comparable data of related compounds like 1.8-diphenylnaphthalene, hexahelicene, and 4-methylbenzo[c] phenanthrenes, and gave evidence for the remarkably small, space-demanding properties of the phenyl substituent in these compounds.     

Conformational Analysis,RIS Models and Single‐Chain Properties of Structurally Modified Polycarbonates, 1. Effect of Cyclohexyl and Phenyl Ring Substitutions

Conformational properties of segments and chains of structurally different polycarbonates are investigated in detail. Conformational analysis and rotational isomeric state (RIS) models for some of the polycarbonates and single‐chain properties of all the polycarbonates are reported here for the first time. Substitution of the methyl group on the bisphenol phenyl rings results in increased energy barriers to rotations as well as changes in positions of local minima, compared to the case without substitutions. Conformational structure about the isopropylidene linkage C_α atom is not altered by ortho methyl substitutions on the rings. Substitution by a cyclohexyl ring rigidly attached to the C_α atom restricts conformational mobility within the bisphenol unit. Rotational flexibility of the phenyl–oxygen bond is hindered by additional substitutions on the cyclohexyl ring. The carbonate group prefers the trans–trans conformation in all the polycarbonates. The energy difference between the cis–trans and trans–trans states of the carbonate group is lowered by the ortho methyl substituent on the phenyl rings. There is a reduction in 〈R²〉, 〈S²〉, and C_n accompanying the substitutions. The introduction of other substituents on a cyclohexyl polycarbonate results in an increase in all chain dimensions including the persistence length. Also, the cyclohexyl or trimethylcyclohexyl substituents do not significantly alter the overall average shape of the chains. Substitutions both on the phenyl rings and at the isopropylidene linkage lead to a compaction of the polymer chain, but the effect is more pronounced when due to substituents on phenyl rings.     

Rotational isomerism—22: An nmr study of oh..π bonding and the conformations of benzyl alcohol and derivatives

The conformations of benzyl alcohol, the ortho and para nitro and methoxy derivatives and benzyl methyl ether have been investigated by NMR in CCL₄ and DMSO solutions. The ³J(CH.OH) and ²J(H.C.H) couplings (the latter via the ²J(H.C.D)coupling)and the OH chemical shift (in DMSO and ∞ dil^XXX as conformational probes. The δ_∞ (OH) for ROH (R = Me, Et, iPr) is also given.The results provide no support for the existence of an intramolecular H-bond in benzyl akohol The endo conformation of the OH proton (anti to a CH proton) is favoured by ca. 1 kcal mole^?1 over the exo conformation (H anti to phenyl) and these conformers are responsible for the separate OH frequencies observed in the IR spectrum. The results do not support an extreme conformation of the phenyl ring (C.C.C.O dihedrals of 0 or 90°) but are consistent with either an 6?0° conformation of the phenyl ring or a freely rotating model. In ortho nitrobenzyl alcohol intramolecular H-bonding is present, but in ortho methoxy benzyl alcohol little or no bonding to the substituent occurs.     

Phenyliodine(V) fluorides

The known compound phenyltetrafluoroiodine(V) is shown by X-ray diffraction to have a tetragonal pyramidal structure with an apical phenyl group. This structure is compared to that of IF(OTeF₅)₄, where the apical position is occupied by the fluorine atom. C₆H₅IF₄ adds F⁻, forming C₆H₅IF₅⁻, which has a pentagonal pyramidal structure with an apical phenyl group. Fluoride abstraction from C₆H₅IF₄ by SbF₅ results in the formation of the cation C₆H₅IF₃⁺, which has a pseudotrigonal bipyramidal structure with the phenyl group occupying an equatorial position. Isoelectronic C₆H₅IOF₂ has a similar structure, with the phenyl group and oxygen atom both occupying equatorial positions.     

A dynamic nmr study of restricted rotation of two substituted phenyl groups in a c/s 1,2-diphenylcyclobutane

Dlmethyl 2,2',6.6'-tetrachloro-b-truxlnale (1) displays restricted rotation of its phenyl groups as evidenced by lineshape analysis of the dynamic¹H and ¹³C NMR spectra with the fallowing activation parameters: ΔH≠ 10.98 ± 0.24 kcal mol^-1, ΔS≠ -4.38 ± 0.99 cal mol^-1K^-1. In the transition state for rotation the two phenyl groups are perpendicular to one another and the act of rotation Involves one phenyl group at a time. The major contribution to the barrier of rotation has its origin In the chlorine atoms. X-Ray analysis of 1 yields a structure with an angle of pucker of 14.3° for the cyclobulane ring in which one chlorine group hovers over the cyclobutane rihg while the two chlorines of the other phenyl group avoid the cyclobutane ring.