3-Aryl- or 3-(trans-4-alkylcyclohexyl)- 6-arylcyclohex-2-enones: synthesis, transformations and mesomorphic properties

The synthesis and chemical transformations of 3-aryl- or 3-(trans-4-alkylcyclohexyl)- 6-arylcyclohex-2-enones into liquid crystalline compounds are discussed. These 3,6-disubstituted cyclohex-2-enones were prepared by the condensation of appropriate Mannich salts or trans-4-alkylcyclohexyl 2-bromoethyl ketones with 4-substituted benzyl methyl ketones.     

3-(2-Cyanoethyl )-6-aryl- or 6-(trans-4-alkylcyclohexyl)cyclohex-2-enones: synthesis, transformations and mesomorphic properties

The synthesis and chemical transformations of 3-(2-cyanoethyl)-6-aryl- or 6-(trans-4-alkylcyclohexyl)cyclohex-2-enones into nematic and smectic liquid crystalline compounds are discussed. These 3,6-disubstituted cyclohex-2-enones were prepared by the condensation of appropriate Mannich salts or trans-4-alkylcyclohexyl 2-bromoethyl ketones with ethyl 2-(2-cyanoethyl)acetoacetate.     

Carbene-carbene rearrangements as a route to 1,5-dihydropentalene

1,5-Dihydropentalene (4) is formed as the main product on treatment of trans-1,2-bis(2,2-dibromocyclo-propyl)ethene 3 with methyllithium at −40°. In addition the reaction affords 1- and 2-propadienylcyclopentadienes (5a) and (5b), and trans-1,2,4,6,7-octapentaene (6), new C₈H₈ isomers. Diels-Alder adducts of 4, 5a and 5b were obt in the reaction with perfluorobut-2-yne. The formation of 1,5-dihydropentalene 4 is explained by a double ring expansion sequence involving consecutive carbene-carbene rearrangements with 1,3-carbon and subsequent 1,2-hydrogen shifts, supported by the reaction of double labelled (¹³C-depleted) 3. From readily available 3 at low temperatures formation and fusion of two 5-membered rings are achieved in one step.     

Carbon-carbon double bond in pillar[5]arene cavity: Selective binding of cis/trans-olefin isomers

The binding behavior of pillar[5]arenes (P5As) towards a series of olefin guests ((E)-1,4-dichlorobut-2-ene (1E), (Z)-1,4-dichlorobut-2-ene (1Z), (E)-but-2-ene-1,4-diol (2E), and (Z)-but-2-ene-1,4-diol (2Z), as well as an alkyne derivative 1,4-dichlorobut-2-yne (3)) have been studied in organic solution. P5As exhibit considerable selectivities for the trans-olefin isomers (1E and 2E) over their cis-isomers (1Z and 2Z). The cis/trans-selective interactions hold the potential of utilizing P5As to separate olefin isomers.     

Synthesis and mesomorphic properties of three- and four-ring liquid crystals containing cyclohexyl, phenyl and pyridyl units

Two series of 4-(3-alkoxycarbonylpyridyl-6-ethynyl)phenyl trans-4-n-alkylcyclohexylcarboxylates and 4-(3-alkoxycarbonylpyridyl-6-ethynyl)phenyl 4-(trans-4-n-alkylcyclohexyl)benzoates have been prepared. Their mesmorphic properties were observed and measured by polarizing optical microscopy and differential scanning calorimetry. The relationship between structures and properties is discussed, showing that the ferroelectric phase can be observed when chiral terminal chains exist.     

Engineering reactions in crystals: suppression of photodecarbonylation by intramolecular β-phenyl quenching

The photochemical reactivity of cis- and trans-2-(p-carboxybenzyl)-2,6-diphenyl-6-vinylcyclohexanone, cis-1 and trans-1, was investigated in solution and in the crystalline solid state. Photochemical decarbonylation in solution proceeded in excellent yields to give cis- and trans-1-(p-carboxybenzyl)-1,2-diphenyl-2-vinylcyclopentanes cis-2 and trans-2 along with 3-(p-carboxybenzyl)-1,3-diphenylcycloheptene 3. Reactions in crystals were suppressed by a stereospecific quenching interaction between the benzyl substituent and the carbonyl oxygen in the crystalline ketone.     

A convenient method of synthesis of mesomorphic 2,5-disubstituted cyclohexan-1-ones by a catalytic reduction of 3,6-disubstituted cyclohex-2-en-1-ones

The preparation of trans-2,5-disubstituted cyclohexan-1-ones from 3,6-disubstituted cyclohex-2-en-1-ones by reduction with hydrogen in the presence of palladium on carbon in a basic medium is described. The nature of the mesomorphic phases together with some physical properties of single compounds and of nematic mixtures comprising them are reported. Mesogens containing the trans-2,5-disubstituted cyclohexan-1-one ring show a small negative dielectric anisotropy and a low birefringence.     

High pressure phase studies of some liquid crystalline cyclohexane derivatives by differential thermal analysis

T(p) phase diagrams for the mesomorphic compounds trans-4-n-butylcyclohexane-1-carboxylic acid 4-cyanophenyl ester (D4N), trans4-n-pentylcyclohexane-1-carboxylic acid 4-n-pentylphenyl ester (D55), trans-4,4'-di-n-propyl-1,1-bicyclohexyl-cis-4-carbonitrile (33CCN), trans-4-methoxy-4'-propyl-1,1'-bicyclohexane (3O1CCH) and trans-4-methoxy-4'-n-butyl-1,1'-bicyclohexane (4O1CCH) are presented. The experiments were performed using high pressure microcomputer-assisted differential thermal analysis equipment in the temperature range 300 to 500 K up to a maximum pressure of 8 kbar. Some special high pressure effects for liquid crystals, such as pressure-induced or pressure-limited phases and changes from monotropic to enantiotropic polymorphism were observed. For the correlation of the experimental results, an extension of the Simon equation was used; one of the regression parameters of the clearing curve equation was found to be correlated with the molecular structure of the liquid crystal substances under test.     

Enantioselective catalytic epoxidation of nonfunctionalized prochiral olefins by dissymmetric chiral Schiff base complexes of Mn(III) and Ru(III) metal ions II

A series of new dissymmetric chiral Schiff base complexes has been obtained by a systematic condensation of (1S,2S)(+)-diaminocyclohexane and 3-acetyl-4-hydroxy-6-methyl-2-pyrone with salicylaldehyde, 5-chloro-, 5-methoxy-and 5-nitrosalicylaldehyde and by subsequent metallation with manganese and ruthenium. The characterization of the complexes 1–8 was accomplished by physico chemical studies viz. microanalysis, IR-, UV/VIS-, and CD spectral studies, optical rotation, molar conductance measurements and cyclic voltammetry. Enantioselective epoxidation of non functionalised olefins, viz. cis-stilbene, trans-3-nonene and trans-4-octene with iodosyl benzene as oxidant was demonstrated in the presence of catalytic amounts of chiral Mn(III) and Ru(III) dissymmetric Schiff base complexes. Good optical yields of epoxides were obtained for the catalyst 4 with the substrates trans-3-nonene and cis-stilbene.     

Two-dimensional assembly of functionalized 4-aryl-1-alkenyl-3,5-dioxo-1,2,4-triazolidines

Acid functionalized derivatives of 4-aryl-1-alkenyl-3,5-dioxo-1,24-triazolidines (4-arylurazoles), i.e. 4-(-but-1-en-3-yl-3, 5-dioxo-1,2,4-triazolidin-4-yl) benzoic acid (1), 4-urazoyl benzamide, i.e. 4-(1-but-1-en-3-yl-3, 5-dioxo-1,2,4-triazolidin-4-yl) benzamide (2), and 4-urazoylphenylazobenzoic acid, i.e. 4-(1-but-1-en-3-yl-3, 5-dioxo-1,2,4-triazolidin-4-yl) phenylazobenzoic acid (3), organize into two-dimensional supramolecular assemblies via intermolecular hydrogen bonding. Hydrogen bonds are formed between two acid (or amide) and two urazole groups, as well as between a carbonyl group of the urazole heterocycle and a hydrogen atom of the phenyl ring. These two-dimensional layers also persist if the polar groups are attached randomly to flexible polybutadiene chains.     

Fluorocyclohexanes-II Cis- and trans- 1H:3H- and 1H:4H-decafluorocyclohexanes

An extension of the methods employed in the isolation of (trans) 1H/2H-decafluorocyclohexane,¹ (I) from the polyfluorocyclohexane mixture obtained by the vapour phase fluorination of benzene with cobaltic fluoride at about 150°, has afforded the four remaining members of the series of decafluorocyclohexanes [the cis- and trans-1H:3H- and 1H:4H-isomers (1H:3H/-(IV), 1H/3H-(III), 1H:4H/-(VII), and 1H/4H-(VIII), respectively)] and also the cis-1H:2H-decafluorocyclohexane (II), obtained previously^1,2 by the lithium aluminium hydride reduction of 1:2-dichlorodecafluorocyclohexane. The structures of the 1H:3H- and 1H:4H-decafluorides have been established by dehydrofluorination studies. The six decafluorocyclohexanes have been related to two new nonafluorocyclohexanes³ (IX and X) by further fluorination of the latter. 2H-Heptafluoroadipic acid has been obtained from 3H-nonafluorocyclohex-1-ene (V), one of the dehydrofluorination products of the 1H:3H-decafluorides.     

Synthesis of substituted quinolines by iron-catalyzed coupling reactions between chloroenynes and Grignard reagents

This letter reports the preparation of quinolines, substituted at the 2- or 3-position by a 4-substituted but-3-en-1-yne group, by the environmentally friendly iron(III)-catalyzed coupling reaction of Grignard reagents with 1-chloro-4-(2-quinolyl)but-1-en-3-yne. The extension and the scope of this non-toxic and chemoselective procedure to various functionalized unsaturated vinyl chlorides are described.     

Stereochemistry of the co-oxidation products of indene and thiophenol

The major primary product of the co-oxidation of indene and thiophenol is trans-2-phenylmercapto-1-indanyl hydroperoxide, which spontaneously rearranges to the two racemes of trans-2-phenylsulphinyl-1-indanol. Attack by the phenylmercaptyl radical on the indene molecule is, within 5 per cent, exclusively at the 2-position and subsequent addition of oxygen to the intermediate 2-phenylmercaptoindanyl radical is, within the same limits, exclusively a trans-addition.

The cis- and trans-2-phenylmercapto-1-indanols and the related sulphoxides and sulphones have been synthesised. Under certain conditions, the substitution reaction of thiophenate ion with indene bromohydrin is accompanied by migration of the hydroxyl group and production of trans-1-phenylmercapto-2-indanol; the sulphoxides and sulphone in this series are also described.     

The synthesis and liquid crystal properties of certain 1-(4'-n-alkoxy-2,2',3,3',5,5',6,6'-octafluorobiphenyl-4-yl)- 2-(trans-4-n-pentylcyclohexyl)-ethanes and -ethenes

The synthesis and liquid crystal properties of eight members of the homologous series of 1-(4'-n-alkoxy-2,2',3,3',5,5',6,6'-octafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)-ethanes and eight members of the corresponding -ethanes, which have the E-configuration, are reported. These compounds are nematic, the ethenes having a considerably mesophase higher thermal stability than the analogous ethanes.     

Syntheses of low-valent nitrosyl complexes of rhenium and X-ray structure oftrans-[ReCl(NO)(Ph2PCH2CH2PPh2)2][NO3]2 with nitrosyl derived nitrates

The nitrosyl complexes trans-[ReCl(NO)(dppe)₂]A₂ (1; A = BF₄ or NO₃; dppe = Ph₂PCH₂CH₂₋PPh₂) and trans-[ReCl(NO)(dppe)₂][BF₄] (2) have been prepared from the reactions of NO[BF₄] or NO with trans-[ReCl(N₂)dppe)₂]. An unusual facile oxidation of NO to nitrate is involved in the formation of (1, A = NO₃), the X-ray structure of which is reported.     

Organometallic complexes for nonlinear optics: Part 32: Synthesis, optical spectroscopy and theoretical studies of some osmium alkynyl complexes

The complexes trans-[Os(CCPh)Cl(dppe)₂] (1), trans-[Os(4-CCC₆H₄CCPh)Cl(dppe)₂] (2), and 1,3,5-{trans-[OsCl(dppe)₂(4-CCC₆H₄CC)]}₃C₆H₃ (3) have been prepared. Cyclic voltammetric studies reveal a quasi-reversible oxidation process for each complex at 0.36–0.39 V (with respect to the ferrocene/ferrocenium couple at 0.56 V), assigned to the Os^II/III couple. In situ oxidation of 1–3 using an optically transparent thin-layer electrochemical (OTTLE) cell affords the UV–Vis–NIR spectra of the corresponding cationic complexes 1⁺–3⁺; a low-energy band is observed in the near-IR region (11 000–14 000 cm⁻¹) in each case, in contrast to the neutral complexes 1–3 which are optically transparent below 20 000 cm⁻¹. Density functional theory calculations on the model compounds trans-[Os(CCPh)Cl(PH₃)₄] and trans-[Os(4-CCC₆H₄CCPh)Cl(PH₃)₄] have been used to rationalize the observed optical spectra and suggest that the low-energy bands in the spectra of the cationic complexes can be assigned to transitions involving orbitals delocalized over the metal, chloro and alkynyl ligands. These intense bands have potential utility in switching nonlinear optical response, of interest in optical technology.     

Syntheses, crystal structures and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

We have systematically investigated the structural features, electronic properties, thermally-induced structural phase transitions and absorption spectra depending on the solvent for ten Cu(II) complexes with 3,5-halogen-substituted Schiff base ligands. Structural characterization of two new complexes, bis(N-R-1-phenylethyl- and N-R,S-2-butyl-5-bromosalicydenaminato-κ²N,O)copper(II), reveals that they afford a compressed tetrahedral trans-[CuN₂O₂] coordination geometry with trans-N–Cu–N = 159.4(2)° and trans-O–Cu–O = 151.7(3)° for the 1-phenylethyl complex and trans-N–Cu–N = 157.9(3)° and trans-O–Cu–O = 151.0(3)° for the 2-butyl one. All the complexes exhibit a structural phase transition by heating in the solid state regardless of their structures at room temperature. The absorption spectra of a series of ten complexes exhibit a slight shift of the d–d band at 16 000–20 000 cm⁻¹ and remarkable shift of the π–π* band at 24 000–28 000 cm⁻¹, which suggests that the dipole moment of the solvents presumably affects the conformation of the π-conjugated moieties of the ligands rather than the coordination environment. We have also attempted ‘photochromic solute-induced solvatochromism’ by a system of bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato-κ²N,O)copper(II) and photochromic 4-hydroxyazobenzene in chloroform solution. We successfully observed a change of the d–d and π–π* bands of the complex in the absorption spectra caused by cis–trans photoisomerization of 4-hydroxyazobenzene.     

Analogues of male sex hormones

The synthesis of cis- and trans-6-(4′-oxocyclohexenyl)-9-methyldecal-1-ol, which may be regarded as analogues of D-homo-testosterone, is described.     

The absolute configuration of trans-1,2-dimethylcyclopropane

By application of the newly discovered fact that 1° alkyl chlorides with γ-hydrogen form cyclopropanes on treatment with sodium metal, (−)-trans-1,2-dimethylcyclopropane has been prepared from (+)-1-chloro-2-methylbutane. Rigorous assignment of configuration to the isomeric cis- and trans-dimethylcyclopropanes is thereby achieved. The absolute configuration, (1R : 2R) trans-1,2-dimethylcyclopropane, can be assigned to the (−) enantiomer by several lines of argument and agrees with that calculated by Fitts.     

Cis- and trans-3-hexene: infrared spectrum in liquid argon solution, ab initio calculations of equilibrium geometry, normal coordinate analysis, and vibrational assignments

The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C₂ and C_s) of cis-3-hexene and of the three lowest energy rotamers (symmetry C_i, C₂, and C₁) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the ΔH of conversion between the rotamers C₂ and C_s of cis-3-hexene and between the rotamers C_i, C₂, and C₁ of trans-3-hexene.