The synthesis of cholest-5-ene-3beta-carboxylates and a comparison of their mesomorphic behaviour with isomeric cholesterol esters with a reversed ester linkage

The syntheses of seven esters of cholest-5-ene-3beta-carboxylic acid are reported and the melting points, transition temperatures and mesophase morphologies of the esters are compared with those of the isomeric 3beta-cholesterol compounds which have the ester link reversed. For the examples reported, the cholest-5-ene-3beta-carboxlates always have significantly lower melting points, but the differences in clearing temperatures for the two series of esters are usually much less. Several of the new compounds give an increased chiral nematic phase range and an intense selective reflection of light. They therefore represent a novel type of chiral nematic material for use in thermochromic applications.     

Mesomorphic properties of troponoid esters and amides with cholest-5-ene-3β-carboxylic acid moiety

Troponoid esters and amides connected with cholest-5-ene-3β-carboxylic acid have been synthesized to characterize their mesomorphic properties and to compare them with those of the corresponding benzenoids. 5-Alkoxytroponyl esters and amides with a long alkoxy group exhibited a twist grain boundary A* phase, as well as chiral nematic and smectic A* (SmA*) phases. The corresponding benzenoid esters exhibit SmA* and blue phases and the benzenoid amides only a SmA* phase. The differences between the mesomorphic properties are discussed in terms of the structural features of the core.     

Unsymmetrical dimers possessing a cholesteryl ester moiety and a difluoro-substituted biphenyl core: synthesis and mesomorphic behaviour

Some new unsymmetrical dimers consisting of a cholesteryl ester moiety, covalently linked to either a 4'-(2,3-difluoro-4-n-octyloxy) biphenyloxy or a 4'-(2,3-difluoro-4-n-decyloxy) biphenyloxy through odd-even parity paraffinic central spacers, have been synthesized and investigated for their mesomorphic behaviour. Except for one, all the dimers exhibit enantiotropic smectic A, twist grain boundary (TGB) and chiral nematic mesophases. Five of the eight unsymmetrical dimers synthesized show a chiral smectic C (SmC*) phase. Interestingly in some of the compounds the SmC* exists over a wide temperature range including room temperature. Among the eight compounds, a dimer having a C₇ central paraffinic spacer and a C₈ alkoxy terminal chain shows an enantiotropic twist grain boundary with SmC* blocks (TGB_C*) phase. It appears that the variation in the length of the spacer has a remarkable influence on the phase transition temperatures as well as on the mesomorphic behaviour.     

Unsymmetrical dimers possessing a cholesteryl ester moiety and a difluoro-substituted biphenyl core: synthesis and mesomorphic behaviour

Some new unsymmetrical dimers consisting of a cholesteryl ester moiety, covalently linked to either a 4′-(1,3-difluoro-4-n-octyloxy) biphenyloxy or a 4′-(2,3-difluoro-4-n-decyloxy) biphenyloxy through odd-even parity paraffinic central spacers, have been synthesized and investigated for their mesomorphic behaviour. Except for one, all the dimers exhibit enantiotropic smectic A, twist grain boundary (TGB) and chiral nematic mesophases. Five of the eight unsymmetrical dimers synthesized show a chiral smectic C (SmC*) phase. Interestingly in some of the compounds the SmC* exists over a wide temperature range including room temperature. Among the eight compounds, a dimer having a C₇ central paraffinic spacer and a C₈ alkoxy terminal chain shows an enantiotropic twist grain boundary with SmC* blocks (TGB_C*) phase. It appears that the variation in the length of the spacer has a remarkable influence on the phase transition temperatures as well as on the mesomorphic behaviour.     

The synthesis and mesomorphic behaviour of tetracatenar di-hydrazine derivatives

Symmetrical four-chained (tetracatenar) di-hydrazine derivatives, namely oxalyl N',N'-bis(3,4-dialkoxybenzoyl)-hydrazide (BFH-n, n?=?4, 6, 8, 10), were synthesised. Investigations on the liquid crystalline properties by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarising optical microscopy (POM) showed that the di-hydrazine derivatives exhibited columnar mesophases and the symmetry of the mesophase changes from rectangular to hexagonal on increasing the temperature. The rectangular columnar mesophases of BFH-n (n?=?6, 8, 10) remained stable down to 10°C during cooling and the subsequent recrystallisation from the Col_r phase of BFH-n (n?=?6, 8, 10) was observed on the second heating runs. Furthermore, the average number of molecules packing in a column slice was estimated to be three, based on their X-ray diffraction results. Intermolecular hydrogen bonding between –C=O and ?N?H groups in crystalline and liquid crystalline phases was confirmed.     

The synthesis of 1-biphenyl-4-alkyl-[1,2,3]-triazoles and their mesomorphic behaviour

A series of 1-biphenyl-4-alkyl-[1,2,3]-triazole-based liquid crystal compounds were synthesised via a fast and efficient microwave mediated ‘Click Reaction’ and their phase behaviour is presented. Most of the 1-(3-fluorobiphenyl)-4-alkyl-[1,2,3]-triazole compounds exhibited a smectic A phase with relatively low transition temperatures compared to previously examined aryl-triazole-based mesogens. Small angle X-ray scattering measurement indicated the existence of deep smectic phase for some cases. Structural variations gave rise to different phase behaviour in these triazole-based compounds.     

The novel rufigallol-based liquid crystals with cholesterol units: synthesis,mesomorphic and photophysical properties

Three novel rufigallol derivatives with four alkyl chains and two cholesteric units 6a, 6b and 6c were prepared in yields of 83–88%. The mesomorphic properties were investigated by DSC, POM and XRD analysis, suggesting that compounds 6a, 6b and 6c possess the ordered hexagonal columnar mesophase. The long alkyl chains contribute to the low phase transition temperature. Sample 6c with four dodecyl chains and two cholesterol units is a room temperature liquid crystal between 31°C and 87°C. Compounds 6a, 6b and 6c also have good fluorescence emission between 400 nm and 500 nm. The studies on CD spectra implied that the chiralities of cholesterol moieties are successfully transferred to the liquid crystalline core. Samples 6a, 6b and 6c are the first fluorescence liquid crystal based on rufigallol core with chiral cholesterol units.     

On triazoles XXXVIII. The reaction of isomeric 5-amino-3-morpholino-1H-1,2,4-triazolylcarbothiohydrazides with ortho esters

The reaction of isomeric differently methylated 5-amino-3-morpholino-1H-1,2,4-triazolylcarbo-thiohydrazides with ortho esters were studied. Except of the case of triethyl orthoacetate instead of the expected [1,2,4]triazolo[1,5-d][1,2,4,6]tetrazepin-5(7H)-thione ( 6 ) derivatives different rearranged products such as 7, 8, 21, 23, 25 , and 27 were obtained, derivatives 23 and 27 representing a novel ring system. Possible explanations were given for the formation of the rearranged products.     

Synthesis and mesomorphic behaviour of new mesogenic compounds possessing a cholesteryl ester moiety connected to a pyrimidine core

New mesogenic compounds containing a cholesteryl ester and a pyrimidine moiety connected through a polymethylene spacer have been prepared. The mode of linkage has been made via -CC- and -CN- to understand the structure-property relationship. Only two compounds with a pentamethylene spacer show mesomorphic behaviour. The mesomorphic behaviour has been investigated by polarizing optical microscopy, differential scanning calorimetry and HRXRD studies. Enantiotropic smectic A, twist grain boundary (TGB) and chiral nematic mesophases are exhibited by the newly synthesized compounds.     

Synthesis and comparison of mesomorphic behaviour of a cholesterol-based liquid crystal dimer and analogous monomers

Oligo/polymerisation of known mesogens constitutes a highly efficient strategy in liquid crystal research due to its potential to generate novel liquid crystal materials with intriguing mesomorphic properties. Here we report the synthesis and comparative studies of a synthetic liquid crystal dimer and two of its monomer analogues. By incorporating cholesterol as the mesogenic group, we designed a flexible scaffold consisting of a hybrid of non-polar hydrophobic chain and polar tetraethylene glycol appended to the cholesteryl mesogens. Detailed studies showed that the two classes of mesogens exhibit the same type of liquid crystal phases with similar dimensions but their transition temperatures varied which can be effectively rationalised by the particular chemical functionalities present in each class of materials.     

α-(Ferrocenyl)-aminomethanephosphonous acids. First synthesis and preparation of their esters with cholesterol and adenosine

The series of aminophosphonous acids bearing the ferrocenyl moiety was obtained by the addition of hypophosphorous acid to Schiff bases of ferrocenecarboxaldehyde. They were subsequently condensed with cholesterol and adenosine to form their cholesteryl and adenosinyl esters. The concurrence reaction of DCC with amine nitrogen atom was observed.     

The synthesis of isomeric 4- and 6-ethoxy-3-ethylpyridines

The synthesis of isomeric 4- and 6-ethoxy-3-ethylpyridines has been effected and a difference in the behavior of substituents in the - and -positions of the isomeric pyridine derivatives has been observed.     

The synthesis and mesomorphic properties of ferroelectric liquid crystals with a fluorinated asymmetric frame

A novel series of ferroelectric liquid crystals with a fluorinated asymmetric frame were synthesized by utilizing optically active (S)-2-, (S)-3-, (S)-4- and (S)-5-fluoroalkanols prepared from corresponding (R)-1,2-epoxyalkanes. Their mesomorphic and physical properties, such as spontaneous polarization, optic tilt angle and response time, were investigated systematically in a series of homologous compounds having the chiral centre at different positions on tails of various lengths. All the compounds exhibited the chiral smectic C phase in a wide range of temperatures and were found to possess a fast response time in spite of the small magnitude of the spontaneous polarization.     

Organocatalytic synthesis of N-Phenylisoxazolidin-5-ones and a one-pot synthesis of beta-amino acid esters

A novel N-heterocyclic carbene (NHC)-catalyzed C-N bond formation by the reaction of alpha,beta-unsaturated aldehydes and nitrosobenzene to N-phenylisoxazolidin-5-ones, followed by an acid-catalyzed esterification and Bamberger-like rearrangement in a mild one-pot protocol leads to N-p-methoxyphenyl (N-PMP) protected beta-amino acid esters.     

The stereocontrolled photoaddition of allene to cyclopent-1-ene-1-carboxaldehydes. A total synthesis of (±) steviol methyl ester and isosteviol methyl ester

The stereochemistry of the photoaddition of allene to hydroindenal 19 is explored. The stereochemistry is proven by conversion into steviol methyl ester 22b and isosteviol methyl ester 24.