A Photochemical/Thermal Switch Based on 4,4′-Bis(benzimidazolio)stilbene: Synthesis and Supramolecular Properties.

Stilbene derivatives are well-recognised substructures of molecular switches based on photochemically and/or thermally induced (E)/(Z) isomerisation. We combined a stilbene motif with two benzimidazolium arms to prepare new sorts of supramolecular building blocks and examined their binding properties towards cucurbit[n]urils (n=7, 8) and cyclodextrins (β-CD, γ-CD) in water. Based on the ¹H NMR data and molecular dynamics simulations, we found that two distinct complexes with different stoichiometry, i. e., guest@β-CD and guest@β-CD₂, coexist in equilibrium in a water solution of the (Z)-stilbene-based guests. We also demonstrated that the bis(benzimidazolio)stilbene guests can be transformed from the (E) into the (Z) form via UV irradiation and back via thermal treatment in DMSO.     

Chlorination of trans-1,2-Diarylethenes in Chloroform and Acetic Acid

When chlorinated in chloroform, (E)-stilbenes bearing electron-donor substituents in the para position of the benzene ring give threo-1,2-diaryl-1,2-dichloroethanes, while meta-substituted (E)-stilbenes, predominantly erythro isomers, irrespective of the nature of the substituent. The reactions in acetic acid result in preferential formation of threo-1,2-dichloro- and threo-1-acetoxy-1,2-diaryl-2-chloroethanes.     

Induction of molecular chirality by circularly polarized light in cyclic azobenzene with a photoswitchable benzene rotor

New phototriggered molecular machines based on cyclic azobenzene were synthesized in which a 2,5‐dimethoxy, 2,5‐dimethyl, 2,5‐difluorine or unsubstituted‐1,4‐dioxybenzene rotating unit and a photoisomerizable 3,3′‐dioxyazobenzene moiety are bridged together by fixed bismethylene spacers. Depending upon substitution on the benzene moiety and on the E/Z conformation of the azobenzene unit, these molecules suffer various degrees of restriction on the free rotation of the benzene rotor. The rotation of the substituted benzene rotor within the cyclic azobenzene cavity imparts planar chirality to the molecules. Cyclic azobenzene 1 , with methoxy groups at both the 2‐ and 5‐positions of the benzene rotor, was so conformationally restricted that free rotation of the rotor was prevented in both the E and Z isomers and the respective planar chiral enantiomers were resolved. In contrast, compound 2 , with 2,5‐dimethylbenzene as the rotor, demonstrated the property of a light‐controlled molecular brake, whereby rotation of the 2,5‐dimethylbenzene moiety is completely stopped in the E isomer (brake ON, rotation OFF), while the rotation is allowed in the Z isomer (brake OFF, rotation ON). The cyclic azobenzene 3 , with fluorine substitution on the benzene rotor, was in the brake OFF state regardless of E/Z photoisomerization of the azobenzene moiety. More interestingly, for the first time, we demonstrated the induction of molecular chirality in a simple monocyclic azobenzene by circular‐polarized light. The key characteristics of cyclic azobenzene 2 , that is, stability of the chiral structure in the E isomer, fast racemization in the Z isomer, and the circular dichroism of enantiomers of both E and Z isomers, resulted in a simple reversible enantio‐differentiating photoisomerization directly between the E enantiomers. Upon exposure to r‐ or l‐circularly polarized light at 488 nm, partial enrichment of the (S)‐ or (R)‐enantiomers of 2 was observed.     

X-Ray Investigation of (E)-2-phenyl-1-chlorocyclopropane-1-carboxylic Acid — A Convenient Synthon for Transamine Synthesis

A method for the synthesis of (E,Z)-2-phenyl-1-chlorocyclopropane-1-carboxylic acid by the addition of ethyl trichloroacetate to styrene in the presence of copper(I) ammine complexes is suggested. The major isomer was isolated as the corresponding acid. The results of X-ray diffraction (XRD) analysis unequivocally prove that the benzene ring and the carboxylic group are in the cis-position and that the molecules form centrosymmetric dimers. (E)-2-phenyl-1-chlorocyclopropane-1-carboxylic acid can serve as a convenient synthon for transamine synthesis.     

Glycosylidene Carbenes. Part 7. Neighbouring-group participation by the 2-benzyloxy group in the glycosidation of strongly acidic hydroxy compounds

To demonstrate the neighbouring-group participation of the 2-benzyloxy group in the glycosidation of phenols and of strongly acidic alcohols by the diazirine 1 , we examined the glycosidation of 4-nitrophenol, 4-methoxyphenol, (CF₃)₂CHOH, MeOH, and i-PrOH by the diazirine 11 , derived from the 2-deoxypyranose 6 . Oxidation of the oximes 7 yielded (E)- and (Z)- 8 . In solution, (E)- 8 isomerised to (Z)- 8 . Similarly, the (E)-configurated mesylate 9 , prepared from 8 , underwent acid-catalysed isomerisation to (Z)- 9 . Treatment of (Z)- 9 with NH₃, followed by oxidation of the resulting diaziridine 10 with I₂, yielded the desired diazirine 11 . Glycosidation by 11 of the above mentioned hydroxy compounds yielded the glycosides 12–21 . In agreement with the postulated neighbouring-group participation, these glycosidation proceeded without, or with a very low diastereoselectivity, favouring the axial anomers.     

Synthesis of all four enantiomers of 1-aminoindane-2-carboxylic acid,a new cispentacin benzologue

Racemic cis- and trans-1-aminoindane-2-carboxylic acids (3 and 5) were prepared from indene by chlorosulphonyl isocyanate addition followed by ring opening and isomerisation. The intermediate racemic hydroxymethylated β-lactam 6 was resolved through the lipase-catalysed asymmetric acylation of the primary hydroxy group at the (R)-stereogenic centre. High enantioselectivities (E>200) were observed when the enzymatic reactions were performed with lipase AK or lipase PS as catalyst and vinyl acetate or vinyl butyrate as acyl donor. The hydrolysis and isomerisation resulted in all four enantiomers (9, 11, 13 and 14) of 1-aminoindane-2-carboxylic acid, a new benzologue of cispentacin.     

Electronegativity and resonance parameters from the geometry of monosubstituted benzene rings

Reference values of the structural substituent parameters, S _E and S _R, measuring the electronegativity and resonance effects, respectively, of functional groups (Campanelli et al. J Phys Chem A 107:6429–6440, 2003) have been determined from the benzene ring geometries of 100 Ph–X species, including different conformations of the same molecule. Geometries have been obtained by quantum chemical calculations at the HF/6-31G*, HF/6-311++G**, and B3LYP/6-311++G** levels of theory. The substituent parameters from HF/6-311++G** calculations are in close agreement with those determined at the HF/6-31G* level. Using the B3LYP density functional yields S _E and S _R values which—in general—correlate well with the corresponding HF values. Exceptions occur with some charged groups, and, in the case of S _E, with a few dipolar groups having very high or low electronegativities. S _R values from B3LYP calculations are about 22% smaller than the corresponding HF values. The variations of the benzene ring geometry caused by electronegativity, resonance, and steric effects are illustrated in some detail.     

Structure of (Z)-(5R)-methyl-2-(4-phenylbenzylidene)cyclohexanone as chiral component of liquid-crystalline systems

The spatial structure of (Z)-(5R)-methyl-2-(4-phenylbenzylidene)cyclohexanone prepared by photochemical isomerization of the E-isomer was studied by analyzing the magnitudes and temperature dependence of the proton spin-spin coupling constants obtained by ¹H NMR spectroscopy and the results of molecular modeling using semiempirical quantum chemical AM1 and PM3 methods and the density functional theory (DFT). Comparison of the results obtained for the Z-and E-isomers shows that in both cases the conformational equilibrium for both isomers is characterized by significant preference of the chair conformer having an equatorial methyl group, namely, − ΔH (chair a ⇌ chair e) = 1.98–2.12 and 1.36–1.54 kcal mole⁻¹ for the Z-and E-isomers, respectively. Distinctions in the non-planarity of the enone fragment and cyclohexanone ring in the Z-and E-isomers under study following from the results of mathematical modeling were confirmed by the experimental values of the geminal spin-spin coupling constants of protons of the methylene groups in α,α ′-positions with respect to the enone group. Quantum chemical calculations of the Z-isomer revealed the existence of intramolecular hydrogen bond between the carbonyl oxygen and the nearest aromatic proton in ortho-position of the benzene ring. Possible reasons for different helical twisting power of (Z)-(5R)-methyl-2-(4-phenylbenzylidene)cyclohexanone and the E-and Z-arylidene derivatives of 1R, 4R-isomenthone in the mesophase are discussed based on the results of molecular structure studies for these compounds. In the text below the unsaturated ketones under study will be called “arylidene cyclohexanone derivatives” for convenience of comparing the characteristics of methylcyclohexanone and isomenthone derivatives. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 962–972, June, 2006.     

Two (E)‐2‐({[4‐(dialkylamino)phenyl]imino}methyl)‐4‐nitrophenols

The slow evaporation of analytical NMR samples resulted in the formation of crystals of (E)‐2‐({[4‐(dimethylamino)phenyl]imino}methyl)‐4‐nitrophenol, C₁₅H₁₅N₃O₃, (I), and (E)‐2‐({[4‐(diethylamino)phenyl]imino}methyl)‐4‐nitrophenol, C₁₇H₁₉N₃O₃, (II). Despite the small structural difference between these two N‐salicylideneaniline derivatives, they show different space groups and diverse molecular packing. The molecules of both compounds are close to being planar due to an intramolecular O—H...N hydrogen bond. The 4‐alkylamino‐substituted benzene ring is inclined at an angle of 13.44 (19)° in (I) and 2.57 (8)° in (II) with respect to the 4‐nitro‐substituted phenol ring. Only very weak intermolecular π–π stacking and C—H...O interactions were found in these structures.     

Volumetric behaviour of binary liquid mixtures of dimethylsulphoxide with substituted benzenes at 303.15 k

Excess molar volumes (V ^E ) for binary mixtures of dimethyl sulphoxide (DMSO) with substituted benzenes have been measured at 303.15?K. The substituted benzenes include toluene, ethylbenzene, chlorobenzene, bromobenzene and nitrobenzene. The measured V ^E data is positive for the mixtures of DMSO with nitrobenzene and is completely negative over the entire composition range in the mixtures of toluene, ethylbenzene and chlorobenzene and an inversion in sign is observed in the bromobenzene system. The experimental results are analysed in terms of intermolecular interactions and effect of substitutents on benzene ring between unlike molecules.     

Vapor–liquid equilibria of 2-butanol + aromatic hydrocarbons at 308.15 k

Vapor–liquid equilibria (VLE) data of 2-butanol?+?benzene or toluene or o- or m- or p-xylene measured by static method at 308.15?±?0.01?K over the entire composition range are reported. The excess molar Gibbs free energies of mixing (G ^E) for these binary systems have been calculated from total vapor pressure data using Barker's method. The G ^E for these binary systems are also analyzed in terms of the Mecke–Kempter type of association model with a Flory contribution term using two interaction parameters and it has been found that this model describes well the G ^E values of binary systems benzene or toluene.     

The molecular and crystal structures of two diastereomeric 3,4-dihydropyrromethenones

The molecular and crystal structures of the two racemic diastereomeric 3,4-dihydropyrromethenone derivatives1 and2 of configurations (Z) and (E) were determined at 93 K (1, 2) and at room temperature (1). From an analysis of the crystallographically observed temperature coefficients a pseudorotation flexibility of the pyrrolidinone ring in the crystal is deduced. In both compounds a nearly orthogonal arrangement between the two heterocyclic ring systems is observed, which is ascribed to the steric bulk of the substituents in positions 1 and 3 of the pyrrolidinone ring.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.     

The first ionization potentials and conjugation in benzene derivatives containing organosilicon, organogermanium, organotin, and organolead substituents

The inductive and resonance effects of silicon-, germanium-, tin-, and lead-containing and some organic substituents on the HOMO energies (E _HOMO) for 43 monosubstituted andp-disubstituted benzene derivatives were analyzed in the Koopmans approximation. A linear dependence between the perturbation energy δE and the resonanceσ _R ⁺ parameters of the substituents was established. The Koopmans approximation is a rough approximation for the compounds studied, since to provide for its rigorous fulfilment, the δE values must depend on the σ _R ⁰ parameters of the substituents. The principal regularities of increasing the σ,π-conjugation between the organoelement substituents and the π-system caused by a positive charge on the benzene ring were established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 70–75, January 1997.     

The Behavior of 3,3-Diphenylindan-1,2-dione Towards Phosphonium Ylides

Summary. The reaction of alkoxycarbonyl- and cyanomethylene(triphenyl)phosphoranes with 3,3-diphenylindan-1,2-dione in dry benzene at room temperature for about 5 h led to the formation of a mixture of (E)- and (Z)-diastereomers. On the other hand, treatment of the dione with acetylmethylene(triphenyl)phosphorane afforded a mixture of (E)-3,3-diphenyl-1-(2-oxo-2-methylethylidene)indan-2-one and unexpected product (E)-3-(3,3-diphenyl-2-oxoindan-1-ylidene)-4-(triphenyl-λ⁵-phosphanylidene)hexane-2,5-dione, whereas with benzoylmethylene(triphenyl)phosphorane gave a mixture of (E)-3,3-diphenyl-1-(2-oxo-2-phenylethylidene)indan-2-one, [(2R ^*,3S ^*)-3-benzoyl-8,8-diphenyl-3,8-dihydro-2H-indeno{2,1-b}furan-2-yl]phenylmethanone and 1,4-diphenyl-2-(3,3-diphenyl-2-hydroxy-3H-inden-1-yl)but-2-ene-1,4-dione. The reaction mechanisms are considered and structural assignments of the new compounds are based on spectroscopic evidence. The molecular structures of the two diastereomers and the unexpected product were elucidated by X-ray crystallography.     

Reduktion von 1,2-bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzol: Synthese von Cyclotrisazobenzol ( = (5E,6aZ,11E,12aZ,17E,18aZ)-5,6,11,12,17,18-Hexaazatribenzo[aei][1,3,5,7,9,11]cyclododeca-hexaen)

Reduction of 1,2-Bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzene¹: Synthesis of Cyclotrisazobenzene ( = (5E,6aZ,11E,12aZ,17E,18aZ)-5,6,11,12,17,18-Hexaazatribenzo[aei][1,3,5,7,9,11]cyclododeca-hexaene) Na₂S reduction of 1,2-bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzene ( 2 ) yielded 3 deoxygenated products: the (known) red 2,2′-((E,E)-1,2-phenylenbisazo)dianiline ( 3 , 23%), the orange 2-[2-((E)-2-aminophenylazo)phenyl]-2H-benzotriazol ( 4 , 55%) and the colorless 2,2′-(1,2-phenylene)di-2H-benzotriazol ( 5 , 13%). The constitutions of 3 – 5 and of 6 , the N-acetyl derivative of 4 , were deduced from their ¹H-NMR spectra (chemical shifts, couplings, and symmetry properties), and the configurations of 3 , 4 , and 6 at their N,N-double bonds are assumed to be the same as in 2 . Oxidation of 3 with 2 mol-equiv. of Pb(OAc)₄ afforded 5 (47%) and a novel, highly symmetrical macrocycle, called cyclotrisazobenzene ( 7 , 24%). The constitution of 7 as a tribenzo-hexaaza[12]annulene and its (E)-configuration at the N,N-bonds was confirmed by X-ray analysis. The molecular symmetry expressed by the ¹H-, ¹³C- and ¹⁵N-NMR spectra of 7 reveals a rapid torsional motion around the six N,C bonds. This implies that the N,N-double bonds in the cyclic 12π-electron system (or 24π-electron system if the benzene rings are included) of 7 are highly localized.     

Azimine. V.. Untersuchungen zur stereoisomerie an der N(2), N(3)-bindung von 2, 3-dialkyl-1-phthalimido-aziminen

Azimines. V. Investigation on the Stereoisomerism Around the N (2), N (3) Bond in 2, 3-Dialkyl-1-phthalimido-azimines 2, 3-(cis-1, 3-Cyclopentylene)-1-phthalimido-azimine ( 7 ) and isomerically pure (2 Z)- and (2 E)-2, 3-diisopropyl-1-phthalimido-azimine ( 9a and 9b ) were prepared by the addition of phthalimido-nitrene ( 1 ) to 2, 3-diazabicyclo [2.2.1]hept-2-ene ( 6 ) and to (E)- and (Z)-1, 1′-dimethylazoethane ( 8a and 8b ), respectively. Comparison of their UV. spectra with those of two stereoisomeric azimines of known configuration, namely (1 E, 2 Z)- and (1 Z, 2 E)-2, 3-dimethyl-1-phthalimido-azimine ( 5a and 5b ), reveals that 2, 3-dialkyl-1-phthalimido-azimines with (2 Z)-configuration are characterized by a shoulder at about 258 nm (? ≈? 14,000) and those with (2 E)-configuration by a maximum at 270–278 nm (? ≈? 10,000). The (2 E)-azimine 9b isomerizes under acid catalysis as well as thermally and photochemically into the more stable (2 Z)-isomer 9a . Under the last two conditions the isomerization is accompanied by a slower fragmentation with loss of nitrogen into N, N′-diisopropyl-N, N′-phthaloylhydrazine ( 4 , R = iso-C₃H₇). The same fragmentation was also observed on thermolysis and photolysis of the (2 Z)-isomer 9a . The kinetic parameters for the thermal isomerization of 9b (they fit first-order plots) and for the fragmentation of 9a and 9b were determined by ¹H-NMR. spectroscopy in benzene, trichloromethane and acetonitrile. In the photolysis of 9a or 9b the fragmentation is accompanied by dissociation into the azo compounds 8a or 8b and the nitrene 1 , the latter being subject to trapping by cyclohexene. With the azimine 7 , an analogous thermal fragmentation was observed to give N, N′-(cis-1, 3-cyclo-pentylene)-N, N′-phthaloylhydrazine ( 15 ), but more energetic conditions were required than with 9 . Photolysis of 7 led exclusively to dissociation into the azo compound 6 and the nitrene 1 , perhaps because the fragmentation of 7 is prevented by ring strain.     

The Behavior of 3,3-Diphenylindan-1,2-dione Towards Phosphonium Ylides

The reaction of alkoxycarbonyl- and cyanomethylene(triphenyl)phosphoranes with 3,3-diphenylindan-1,2-dione in dry benzene at room temperature for about 5 h led to the formation of a mixture of (E)- and (Z)-diastereomers. On the other hand, treatment of the dione with acetylmethylene(triphenyl)phosphorane afforded a mixture of (E)-3,3-diphenyl-1-(2-oxo-2-methylethylidene)indan-2-one and unexpected product (E)-3-(3,3-diphenyl-2-oxoindan-1-ylidene)-4-(triphenyl-λ⁵-phosphanylidene)hexane-2,5-dione, whereas with benzoylmethylene(triphenyl)phosphorane gave a mixture of (E)-3,3-diphenyl-1-(2-oxo-2-phenylethylidene)indan-2-one, [(2R ^*,3S ^*)-3-benzoyl-8,8-diphenyl-3,8-dihydro-2H-indeno{2,1-b}furan-2-yl]phenylmethanone and 1,4-diphenyl-2-(3,3-diphenyl-2-hydroxy-3H-inden-1-yl)but-2-ene-1,4-dione. The reaction mechanisms are considered and structural assignments of the new compounds are based on spectroscopic evidence. The molecular structures of the two diastereomers and the unexpected product were elucidated by X-ray crystallography.     

Excess molar volumes of binary mixtures of 4-methyl-2-pentanone and some hydrocarbons

Summary Excess molar volumes (V ^E) for binary mixtures of 4-methyl-2-pentanone and some hydrocarbons (cyclohexane, benzene, toluene, andp-xylene) over the whole mole fraction range are determined by density measurement at 293.15 K. The variation of theV ^E values with the composition for all binary systems is symmetrical except for benezene where the dependence is sigmoid. TheV ^E values are positive for the binary mixture of the ketone with cyclohexane. For the other hydrocarbons, theV ^E values are progressively negative over the entire mole fraction range except the system containing benzene, where a few values at higher mole fractions of benzene are positive. The results are discussed in terms of molecular interactions steric effects.

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Molare Zusatzvolumina von binären Mischungen von 4-Methyl-2-pentanon und einigen Kohlenwasserstoffen

Zusammenfassung Molare Zusatzvolumina (V ^E) von binären Mischungen von 4-Methyl-2-pentanon und einigen Kohlenwasserstoffen (Cyclohexan, Benzol, Toluol undp-Xylol) wurden bei 293.15 K durch Dichtemessungen über den gesamten Molenbruchbereich bestimmt. Mit Ausnahme der binären Mischung mit Benzol (sigmoide Kurvenform) ist die Änderung vonV ^E in Abhängigkeit von der Zusammensetzung der Mischungen symmetrisch. Für das System Keton/Cyclohexan sind dieV ^E-Werte stark positiv, während sie für die anderen Gemische negativ sind. Eine Ausnahme bildet wieder das System mit Benzol als Kohlenwasserstoff, wo einige Werte bei höheren Molenbrüchen von Benzol positiv sind. Die Ergebnisse werden im Zusammenhang mit intermolekularen Wechselwirkungen und dem Einfluß sterischer Faktoren diskutiert.

     

Synthesis and stereochemical assignment of 7-arylidene and 7-heteroarylidene morphinan-6-ones

A number of (E)-7-arylidenenaltrexones were synthesized by azeotropic distillation of water from a benzene solution of naltrexone and an aromatic aldehyde (benzaldehyde, 4-chloro- and 4-fluorobenzaldehyde, 3-and 4-pyridinecarboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde) using piperidine as a catalyst. In addition, (E)-7-benzylidenenaloxone was prepared by the previously published Claisen-Schmidt condensation using sodium hydroxide in methanol. The stereochemistry of these arylidene derivatives 3–9 was determined to be (E) by means of nuclear Overhauser enhancement experiments. The ¹³C nmr spectra of (E)- 3–9 are recorded in deuteriochloroform and those of the hydrochlorides in deuteriodimethyl sulfoxide.