Conformations of highly hindered aryl ethers—IV PMR studies of 2,4- and 2,6- dinitroaryl ethers

PMR studies of a series of 2,4- and 2,6- dinitrophenyl- and 2,4-dinitronaphthyl- aryl ethers strongly indicate the existence of preferred conformations. Extensive conjugation of the ether linkage with the dinitro ring, resulting in their coplanarity, is an important stereochemical influence. In the ensuing skew conformation the dinitro ring is positioned in such a way that the 6-substituent is proximal to the other ring. In the case of the 2,4-dinitrophenyl ethers ( 1 ) this is the 6-proton, which shows the expected shielding due to the ring current in the other ring. In the 2,6-dinitrophenyl-( 2 ) and 2,4-dinitronaphthyl-( 3 ) ethers, this is a nitro group, twisted out of coplanarity to fit over the other ring, whose magnetic anisotropy is reflected in the shielding experienced by the 6′-protons. When there is a 2′-substituent present the ring which bears it twists in such a way as to bring the 6′-proton closer to the proximal nitro-group, explaining the greater shielding observed in these cases. Variable temperature studies provided further evidence in favor of these conformations since no significant changes were observed from ?55° to + 155°, even for compounds with four substituents flanking the ether linkage. Nevertheless, the compounds studied here are not frozen in these conformations, but probably inter-convert via concerted rotation with others.     

Conformations of highly hindered aryl ethers: XXIII–PMR evidence for preferred conformations and intramolecular π complex formation in nitrophenyl naphthyl ethers

The PMR spectrum of 2-bromo-4,6-dinitrophenyl 2′-naphthyl ether ( 1 ) is consistent with the preferential adoption of a twist conformation ( 1a ) in which the 6-nitro group and the 1′-hydrogen are located endo to the ether link. This preference is explained by the formation of an intramolecular π complex between the 6-nitro group and the C1′? C2′ bond, which is stronger than that formed with the C2′? C3′ bond, in accord with their bond orders. This study adduces further evidence in favor of: (a) the adoption of twist conformations by these and related ethers, (b) the importance of intramolecular π complex formation as a conformational influence, (c) the formation of complexes in such cases is with specific portions of, and not the complete, π cloud and (d) indicates that similar effects may be discerned in analogous ethers related to the thyroid hormones.     

几种三相催化剂在氰代、碘代和二氯卡宾反应中的催化行为

本工作研究了带含氧冠醚、氮杂冠醚、酚醛型冠醚、开链冠醚的四种聚合物作为三相催化剂在氰代、碘代和二氯卡宾反应中的催化活性,其中以冠醚环上带有叔胺氮原子的氮杂冠醚聚合物催化活性最好。     

Synthesis and Evaluation of Paromomycin Derivatives Modified at C(4′)

The 2‐amino‐2‐deoxy‐α‐D ‐glucopyranosyl moiety (ring I) of paromomycin was replaced by a 2,4‐diamino‐2,4‐dideoxy‐α‐D ‐glucopyranosyl, 2,4‐diamino‐2,4‐dideoxy‐α‐D ‐galactopyranosyl, 2‐amino‐2‐deoxy‐α‐D ‐galactopyranosyl, or 3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosyl moiety to investigate the effect of the substituent at C(4′) on the interaction with ribosomal RNA. The triflate 6 was prepared from the key intermediate pentaazido 3′,6′‐dibenzyl ether 5 , and the hexosulose 10 was obtained by oxidation of 5 with Dess–Martin's periodinane. Stereoselective reduction of 10 with NaBH₄ gave the alcohol 11 that was transformed into the triflate 12 . The epimeric hexaazides 7 and 13 were obtained by treating the triflates 6 and 12 , respectively, with tetrabutylammonium azide. Periodate cleavage of glycol 2 yielded the dialdehyde 24 that was reductively aminated with aniline and benzylamine to give the 3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosides 25 and 26 , respectively. Standard azide reduction and debenzylation yielded 9 (2,4‐diamino‐2,4‐dideoxy‐α‐D ‐galactopyranosyl ring I), 13 (2‐amino‐2‐deoxy‐α‐D ‐galactopyranosyl ring I), 17 (2,4‐diamino‐2,4‐dideoxy‐α‐D ‐glucopyranosyl ring I), and 27 and 28 (3,4,5‐trideoxy‐4‐aza‐α‐D ‐erythro‐heptoseptanosyl ring I). The derivatives 9 and 13 possessing a D ‐galacto‐configured ring I were less active than the corresponding D ‐gluco‐analogues 17 and paromomycin ( 1 ), respectively. The C(4′)‐aminodeoxy derivative 17 (D ‐gluco ring I) and the known 4′‐deoxyparomomycin ( 23 ), prepared by a new route, displayed slightly lower antibacterial activities than paromomycin ( 1 ). Cell‐wall permeability is not responsible for the unexpectedly low activity for 17 , as shown by cell‐free translation assays. The results evidence that the orientation of the substituent at C(4′) is more important than its nature for drug binding and activity.     

Thermische Umwandlung von Phenyl-penta-2,4-dienyläthern in 4-[Penta-2,4-dienyl]-phenole als Beispiel für [5,5]-sigmatropische Umlagerungen. Vorläufige Mitteilung

The reaction between phenol and trans penta-2,4-dienyl chloride gave trans penta-2,4-dienyl Phenyl ether (I), whereas with a mixture of sorbyl chloride and 1-methylpenta-2,4-dienyl chloride, pure trans, trans hexa-2,4-dienyl phenyl ether (IV) and trans 1-methylpenta-2,4-dienyl phenyl ether (V) were obtained. The ether I gave, on heating in dilute solution at 185°, 4-(penta-2,4-dienyl)-phenol (III) as the main product, and also some 2-(2-vinylallyl)-phenol (II). The ether IV provided, on heating at 165°, in addition to the ortho CLAISEN rearrangement product VI, mainly a mixture consisting of 94% 4-(1-methylpenta-2,4-dienyl)-phenol (VIII) and only 6% 4-(hexa-2,4-dineyl)-phenol(IX). The latter product (IX) was the only para isomer produced on heating ether V, but in addition 22% of the ortho rearrangement product VII was formed. The migrations I → III, IV → VIII, and V → IX, proceeding through a ten membered transition state, are the first [5,5] sigmatropic rearrangements described.     

Conformations of highly hindered aryl ethers—XVIII : neighboring-ring anisotropy effects in poly(2,4-dinitrophenoxy)benzenes

A PMR study of ten poly-(2,4-dinitrophenoxy)benzenes and naphthalenes together with appropriate reference compounds, showed that (1) relatively long-range anisotropic effects are observed; (2) these are roughly additive when several benzene rings are present; (3) in the absence of steric effects there is no preference between syn and anti dispositions of substituting rings about the central ring; (4) concerted libration and concerted rotation occur freely even in highly substituted diaryl ethers; and (5) a twist conformation is preferred about the individual ether links.     

Three sterically hindered 6‐amino‐5‐cyano‐2‐methyl‐4‐(1‐naphthyl)‐4H‐pyran‐3‐carboxylate derivatives

In the title compounds, 2‐methoxyethyl 6‐amino‐5‐cyano‐2‐methyl‐4‐(1‐naphthyl)‐4H‐pyran‐3‐carboxylate, C₂₁H₂₀N₂O₄, (II), isopropyl 6‐amino‐5‐cyano‐2‐methyl‐4‐(1‐naphthyl)‐4H‐pyran‐3‐carboxylate, C₂₁H₂₀N₂O₃, (III), and ethyl 6‐amino‐5‐cyano‐2‐methyl‐4‐(1‐naphthyl)‐4H‐pyran‐3‐carboxylate, C₂₀H₁₈N₂O₃, (IV), the heterocyclic pyran ring adopts a flattened boat conformation. In (II) and (III), the carbonyl group and a double bond of the heterocyclic ring are mutually anti, but in (IV) they are mutually syn. The ester O atoms in (II) and (III) and the carbonyl O atom in (IV) participate in intramolecular C—H...O contacts to form six‐membered rings. The dihedral angles between the naphthalene substituent and the closest four atoms of the heterocyclic ring are 73.3 (1), 71.0 (1) and 74.3 (1)° for (II)–(IV), respectively. In all three structures, only one H atom of the NH₂ group takes part in N—H...O [in (II) and (III)] or N—H...N [in (IV)] intermolecular hydrogen bonds, and chains [in (II) and (III)] or dimers [in (IV)] are formed. In (II), weak intermolecular C—H...O and C—H...N hydrogen bonds, and in (III) intermolecular C—H...O hydrogen bonds link the chains into ladders along the a axis.     

2‐Bromo‐1,3‐bis[2‐(2‐naphthyl)vinyl]benzene benzene hemisolvate and 9‐bromodinaphth[1,2‐a:2′,1′‐j]anthracene

2‐Bromo‐1,3‐bis[2‐(2‐naphthyl)vinyl]benzene benzene hemisolvate, C₃₀H₂₁Br·0.5C₆H₆, (I), with two formula units in the asymmetric unit, exists in the crystal structure in a conformation in which the trans (2‐naphthyl)vinyl substituents on the central bromobenzene moiety appear as nearly fully extended `wings', while 9‐bromodinaphth[1,2‐a:2′,1′‐j]anthracene, C<sub>30</sub>H<sub>17</sub>Br, (II), adopts a highly nonplanar `manta‐ray' shape, with the H atoms in the interior of the molecule within van der Waals contact distances. The packing of the significantly twisted molecules of (I) generates large voids which are filled by benzene solvent molecules, while molecules of (II) stack compactly with all C—Br bonds parallel within the stack.     

Conformations of highly hindered aryl ethers: XV. Mesomeric moments in m-dinitrobenzenes

The dipole moments of fourteen m-dinitrobenzenes with different substituents (OMe, CN, CH₃, CHO, Cl, CF₃, COOMe, F, Br, NH₂) in various positions were measured in order to study mesomeric interactions. Inclusion of conformational considerations permitted estimates to be made for the mesomeric moments of these groups at given positions. The values obtained could be applied with consistent results to a total of forty m-dinitrobenzenes, including others previously reported. The mesomeric moment increments deduced, compared with substituted benzenes possessing no nitro groups, were found to be only slightly larger than in non-nitro substituted benzenes (compared with substituted alkanes), which would indicate a reluctance of the extended π system of m-dinitrobenzene to interact with other substituents present, in any way other than by direct extension of the π network.One apparent case of intermolecular electron donor-acceptor complex formation was detected. The measured dipole moment of o-iodoanisole indicates a planar anti conformation for the methoxyl group.     

Molecular orbital calculations of poly(vinylidene fluoride) and its model compounds

Calculations of dipole moments of poly(vinylidene fluoride)(PVDF) and its model compounds were performed by the MNDO method. 2,2-difluoropropane as a model compound was found to have a dipole moment of 8.97 × 10^?30 C m (2.69 D). It was in satisfactory agreement with a previously obtained experimental value, 8.01 × 10^?30 C m. Dipole moments of two other model compounds, tetrafluoropentane and octafluorononane, were calculated to be 1.70 and 3.24 × 10^?29 C m, respectively. Ratios of repeat unit moments of the second and third compounds to the first compound moment were equal to 0.95 and 0.90, respectively. These were nearly identical with a theoretical ratio, 0.96, derived from the free rotation model of a polymer chain. The calculated dipole moments were considered to reflect the molecular structures in which free rotations of nearly tetrahedral bond angles might be allowed around C—C links. Dipole moments of each monomer unit for three polymorphs of PVDF, Form I, II, and III were calculated to be 7.64, 5.40, and 5.07 × 10^?30 C m, respectively. Ratios of the three moments to the first model compound moment were found to be 0.85, 0.60, and 0.57. The decreasing order of the three factors suggests that orientations of monomer unit dipoles are more and more interdependent, and free internal rotations around skeletal bonds are more and more hindered, when the conformation varies from Form I to III. Also it was confirmed that the atomic charge distributions of the three polymorphs were very similar, and that the difference in dipole moments were primarily caused by conformation changes of the polymer chain.     

3,6‐Bis(2‐pyridyl)di‐1,2,4‐triazolo­[3,4‐a:4′,3′‐c]­phthalazine

The title compound, C₂₀H₁₂N₈, (I), has been prepared by the reaction of 1,4‐dihydrazinophthalazine and pyridine‐2‐carbox­aldehyde, followed by an oxidative cyclization by treatment with bromine. In the solid state, the mol­ecules of (I) are discrete, comprising a fused and twisted four‐ring system with an overall helical appearance. The distance between the two intramolecular pyridyl N atoms is 3.075 (2) Å, this short contact distance suggesting a π–π interaction.     

Conformations of highly hindered aryl ethers—VIII Interannular H?F coupling in diphenyl ethers

A novel type of interannular coupling (⁶J_H,F = 1.0 to 1.3 Hz) has been observed in some fluorodinitrodiphenyl ethers between the fluorine(s) on one ring ortho to the ether linkage and a proton ortho to it on the other ring. ¹H and ¹⁹F chemical shift and coupling constant data support the previous conclusion that these ethers preferentially adopt a twist (propeller) conformation. On account of the geometrical disposition of the six bonds between the interacting nuclei and the latter's spatial proximity in this conformation, direct coupling through-space is indicated. Concerted libration around the ether bonds brings about magnetic equivalence of the o-fluoro substituents on one ring and causes equal coupling to be observed to the o-proton on the other ring. The possiblity that the coupling is mediated by an intervening π-cloud is suggested as an alternate mechanism for indirect coupling. The observed interannular transmission of spin information provides evidence in favor of a recent proposal made concerning the mode of action of the thyroid hormones.     

Conformation of N‐methyl‐4‐piperidyl 2,4‐dinitrobenzoate

The crystal structure of N‐methyl‐4‐piperidyl 2,4‐di­nitro­benzoate, C₁₃H₁₅N₃O₆, (I), at 130 (2) K reveals that, in the solid state, the mol­ecule exists in the equatorial conformation, (Ieq). Thus, the through‐bond interaction present in the axial conformation, (Iax), is not strong enough to overcome the syn–diaxial interactions between the axial methyl substituent and the axial H atoms on the two piperidyl ring C atoms either side of the ester‐linked ring C atom. The carboxyl­ate group in (I) is orthogonal to the aromatic ring, in contrast with other 2,4‐di­nitro­benzoates, which are coplanar. The piperidyl–ester C—O bond distance is 1.467 (3) Å, which is actually shorter than other equatorial cyclo­hexyl–ester C—O distances. This shorter piperidyl–ester C—O bond distance is due to the reduced electron demand of the orthogonal ester group.     

吩噻嗪给体受体衍生物激发态的电荷转移

A series of N-bonded donor-acceptor derivatives of phenothiazine containing phenyl （PHPZ）, anisyl （ANPZ）, pyridyl （PYPZ）, naphthyl （NAPZ）, acetylphenyl （APPZ）, and cyanophenyl （CPPZ） as an electron acceptor have been synthesized. Their photophysical properties were investigated in solvents of different polarities by absorption and emission techniques. These studies clearly revealed the existence of an intramolecular charge transfer （ICT） excited state in the latter four compounds. The solvent dependent Stokes shift values were analyzed by the modified Lippert-Mataga equation to obtain the excited state dipole moment values. The large excited state dipole moment suggests that the full （or nearly full） electron transfer take place in the A-D systems. In the system of A-D phenothiazine derivatives, the transition dipole moments Mflu were determined mainly by direct interactions between the solvent-equilibrated fluorescence ^1CT state and ground state because of their lack of significant change with increase of the solvent polarity. The electron structure and molecular conformation of phenothiazine derivatives will be significantly changed with the increase of the electron affinity of the N-10 substituent.     

Conformations of highly hindered aryl ethers. XXI—fragementation paths involving intramolecular π-complexes and cyclizations in the mass spectra of 2,4-dinitrophenyl 2′-alkylphenyl ethers

The mass spectrometric study of 2,4-dinitrophenyl 2′-R-phenyl ethers (R ? H, Me, Et, i-Pr, tert-Bu) showed that (1) fragmentation proceeds differently from unsubstituted and 4-nitro-substituted diphenyl ethers; (2) important fragmentation routes involve interannular migrations and cyclizations; (3) these occur between two groups ortho to the ether linkage while the ethers are in unfavorable endo, endo twist conformations; (4) the observed interannular interactions can be ustified by the existence in these compounds of an intramolecular π-complex which stabilizes the sterically unfavorable conformation and explains the observed fragmentations.     

Isomere Tritolylphosphine und deren Derivate. UV-Spektren und Dipolmomente

The UV spectra of tris(2-methylphenyl)phosphine (I), tris(3-methylphenyl)phosphine (II), tris(4-methylphenyl)phosphine (III), and of their phosphine oxides, phosphine sulfides, and methyl phosphonium iodides are given. The dipole moments of I–III in benzene at 20° C were also determined. I absorbs at the longest wavelength and this result may be interpreted by a broadening of the angle on phosphorus in I. This results also from the measured dipole moment, assuming a constant phosphorus ring moment and neglecting other ortho-effects.     

3‐(2‐Furyl)‐6‐(4‐methyl­phenyl)‐7H‐1,2,4‐triazolo­[3,4‐b][1,3,4]thia­diazine and its 6‐phenyl analogue

In the title compounds, C₁₅H₁₂N₄OS, (I), and C₁₄H₁₀N₄OS, (II), the thia­diazine ring adopts a skew‐boat conformation, while the triazole and furyl rings are essentially planar. The phenyl group is twisted by 33.5 (2) and 47.9 (1)° out of the triazole‐ring plane in (I) and (II), respectively.     

STRUCTURE STERIQUE DES COMPOSES CYCLIQUES DU PHOSPHORE. XIII. ETUDE PAR MOMENT DIPOLAIRE DES OXO-2 ET THIO-2 PERHYDRO OXAZAPHOSPHORINES-1,3,2

Abstract

L'étude par moment dipolaire de la conformation de huit perhydro oxazaphosphorines-1,3,2 est décrite. The conformation of eight perhydro 1,3,2-oxazaphosphorines is studied by means of dipole moments.     

(Triphenylarsine)iodinemonobromine: a charge‐transfer adduct in which arsenic selectively bonds to iodine

The title molecule, (iodobromo)triphenylarsenic(III), [As(BrI)(C₆H₅)₃], has a dart shape, with the phenyl rings arranged in a propeller conformation [I—As—C—C 61.3 (4), 43.8 (4) and 54.1 (4)°]. There is no indication that the halogen atoms have mixed site occupancies. Packing forces displace the I atom away from one phenyl ring [I—As—C 117.3 (2)°] towards the other two [I—As—C 109.8 (2) and 108.3 (2)°] and produce an even more pronounced leaning of the terminal bromine [As—I—Br 174.78 (2)°].