Crystal structures of ferro- and antiferroelectric mesogens with a 1-methylalkoxycarbonyl group

Crystal structures have been determined for 4-[(S)-1-methylpentyloxycarbonyl]phenyl, 4-([S)-1-methylhexyloxycarbonyl]phenyl 4'-octyloxybiphenyl-4-carboxylates (1 and 2, respectively) and (R)-1-methylheptyl 4-(4'-octyloxybiphenyl-4-yloxymethylene)benzoate (3), which have S_CA*, S_C* and S_CA* phases, respectively. All the crystals have a common packing mode with the previously determined structure of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC). Each crystal forms a smectic-like layer structure composed of largely bent molecules with the long alkyl chain of the chiral group almost perpendicular to the core moiety. Differential scanning calorimetry showed that the crystals of 1, 2, and MHPOBC, which have a carbonyloxy group as the central linkage between the biphenyl and phenylene moieties, transform to higher temperature solid phases in a similar temperature range (around 60°C). For 3, which has an oxymethylene linkage between the biphenyl and phenylene moieties, three kinds of solids were distinguished.     

Ferroelectric liquid crystals with fluoro- and aza-fluorenone cores: the effect of stereo-polar coupling

The chiral fluorenone mesogens (R)-1-fluoro-2-(2-octyloxy)-7-(4-undecyloxybenzoyloxy)fluoren-9-one (2) and (R)-2-(2-octyloxy)-7-(4-undecyloxybenzoyloxy)-3-azafluoren-9-one (3) were synthesized using a combined ortho-directed and remote metalation strategy, which also incorporates a Suzuki-Miyaura crosscoupling step. These compounds form chiral SmC* liquid crystal phases with reduced polarizations (P _o) of +475 and +332 nC cm^-2 at 10 K below the Curie point, respectively. These values are considerably larger than that previously reported for the unsubstituted fluorenone (R)-2-(2-octyloxy)-7-(4-undecyloxybenzoyloxy)fluoren-9-one (1), which is +111 nC cm^-2 at 10 K below the Curie point. Molecular modelling based on the Boulder model suggests that the larger polarizations result from a conformational bias of the fluorenone core dipole moment along the polar axis of the SmC* phase caused by stereo-polar coupling with the chiral 2-octyloxy side chain.     

New TGBA series exhibiting a SC*SASA*N* phase sequence

A new series with a chiral tolane core has been synthesized. These materials belong to the optically active series: 3-fluoro-4-[(R) or (S)-1-methylheptyloxy]4'-(4'-alkyloxy-3'-fluorobenzoyloxy)tolanes (nFBTFO₁M₇). For the first time, the helical S_A* phase or TGB_A phase is found in all of the derivatives from heptyloxy to octadecyloxy. The S_A-S_A*-N* phase sequence is observed in several compounds with short chains and the S_C*-S_A-S_A*-N* phase sequence is obtained with the decyloxy derivative. The TGB_A phase has filament or cholesteric textures. The helical pitch of the TGB_A phase is short for the octadecyloxy derivative and is compared with that for different chain lengths as a function of temperature. The layer spacing in the TGB_A phase shows that it is incommensurate with the fully elongated molecular length.     

The substituent effect on mesomorphic properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy)benzoates and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates

The thermal properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy) benzo-ates (1) and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates (2) have been examined, where R = hydrogen, halogens, alkyl and alkoxy groups. The derivatives of compound 1 incorporating hydrogen, halogens, methoxy and nitro groups show a smectic A phase having a bilayer arrangement, and the others with a long alkoxy group show the S_A phase with the monolayer arrangement. The derivatives of compound 2 incorporating halogens, and the nitro group show the S_A phase with the monolayer arrangement. The alkoxy derivatives show a smectic C phase as well as the nematic phase. The nitro group at the lateral position tends to increase the ratio of the S_A-N transition temperature to the N-I. The effect of the nitro group on the smectic properties has been discussed in terms of the structural and electrostatic nature of the nitro group.     

Two new acetylated ginsenosides from the roots of Panax quinquefolium

Two new acetylated ginsenosides, 20（S）-protopanaxatriol-6-O-α-L-rhamnopyranosyl （1 → 2）-β-D-6＇-O-acetylglucopyranoside （1） and 20（R）-protopanaxatrol-6-O-α-L-rhamnopyranosyl （1 → 2）-β-o-6＇-O-acetylglucopyranoside （2）, were isolated from the roots of Panax quinquefolium. The structures were elucidated on the basis of spectroscopic techniques and chemical means.     

Synthesis and properties of optically active 1,3-diols and their derivatives as chiral dopants for ferroelectric liquid crystals

New chiral dopants β-hydroxy ketones 1, 1,3-diols 2, 1,3-dioxanes 3 and 1,3-dioxan-2-ones 4 were designed and synthesized. Reaction of (R)-1,2-epoxyoctane with carbanions derived from 2-(4-substituted phenyl)-1,3-dithianes followed by hydrolysis of the resulting hydroxy dithianes afforded 1. Reduction of 1 gave the diols 2, which yielded 3 upon acetalization and 4 upon carbonation. The syn isomers of 2, 3, and 4 exhibited larger spontaneous polarizations, when applied as chiral dopants, than the anti isomers or hydroxy ketones 1.     

First Total Synthesis of (±)-Ponganone Ⅲ

In recent years, the synthesis and pharmacology of pyranoflavanoids have been extensively investigated due to their wide range of pharmacological properties^[1-3]. Ponganone Ⅲ^[4],a new natural pyranoflavanone isolated from the Pongamia pinnala, was identified as (2S)-3',4'-dimethoxy-6',6"-dimethylpyrano-[2",3":7,8]-flavanone (2) on the basis of spectra data. Its precursor,3,4-dimethoxy-2'-hydroxy-6",6"-dimethylchromeno-[2",3":4',3']-chalcone (1) is also a new natural product^[5] isolated from the roots of Lonchocarpus subglaucescent. Their total synthesis have not been reported. Herein, we wish to report the first total synthesis of compounds 1 and 2 in order to confirm the proposed structure and further more to evaluate its biological activities.     

Ferroelectric liquid crystals induced by atropisomeric biphenyl dopants: the effect of chiral perturbations on achiral dopants

The addition of the achiral biphenyl dopant 2,2',6,6'-tetramethyl-4,4'-bis(4-n-nonyloxybenzoyloxy)biphenyl (3) or its dithionoester or dithioester analogue (4, 5) to a 4 mol % mixture of the atropisomeric biphenyl dopant (R)-2,2',6,6'-tetramethyl-3,3'-dinitro-4,4'-bis(4-n-nonyloxybenzoyloxy)biphenyl, (R)-1, in the phenylpyrimidine SmC host PhP1 produces a significant amplification of the spontaneous polarization induced by (R)-1. This amplification may be due to a chiral perturbation by (R)-1 which causes a shift in the equilibrium between enantiomeric conformations of the achiral dopant. The degree of polarization amplification afforded by the achiral dopant, as expressed by the polarization amplification factor PAF, varies with the nature of the linking group. This may be ascribed to different rotational distributions of the core transverse dipole moments relative to the polar axis of the SmC* phase and/or to differences in lateral bulk of the polar linking groups. The latter may affect the degree of chiral molecular recognition achieved by 3-5 in the binding site of the SmC* phase.     

(S)-Isoleucine and (R)-2-octanol as chiral precursors of new chiral liquid crystalline thiadiazoles: synthesis, mesomorphic and ferroelectric properties

New chiral Schiff bases with a 1,3,4-thiadiazole unit in the rigid core were synthesized (SB1-SB4). These compounds contain a chiral chain derived from (S)-isoleucine and (R)-2-octanol. Their liquid crystalline properties were studied by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. Thereby it was found that most of the new compounds exhibit a chiral Smectic C phase. A study of the ferroelectric properties is described.     

Induction of nematic cholesteric (N*) phases by charge transfer complexation of disc-shaped multiynes [1]

Based on charge transfer interactions with the (chiral) electron acceptor (-)-2-(2,4,5,7-tetranitro-9-fluorenylidenaminooxy)propionic acid ((-)-TAPA), our easily accessible disc-shaped electron rich multiynes (for example, 1 and 2) give rise to two types of cholesteric nematic phases. Thus, the binary mixture of the nematic discotic (N_D) pentakis-(4-methylphenylethynyl)phenyl hexadecyl ether (2) with (-)-TAPA exhibits its twisted variant (N*_D). Likewise, but now in a ternary mixture, the homologue 1—peripherically unsubstituted and non-mesogenic—with the two electron acceptors (-)- TAPA and 2,4,7-trinitrofluorenone—both also non-liquid crystalline—shows cholesteric nematic properties, most probably however of a columnar type (N*_C). First results concerning these charge transfer induced cholesteric-nematic properties, including phase diagrams and the helical twist of the two systems presented here, are discussed on the basis of data obtained by polarizing microscopy and differential scanning calorimetry.     

Heterocyclic benzoxazole-based liquid crystals

The synthesis, characterization, and mesomorphic properties of a new type of heteronuclear compounds 1a-c and a Pd complex 1d derived from benzoxazole as the core group are reported. These compounds were prepared by the ring closure reaction of 4-alkoxybenzoic acid 4-[(4-alkoxy-2-hydroxyphenylimino)methyl]phenyl esters 6 in the presence of lead(IV) acetate. All the compounds were characterized by ¹H and ¹³C NMR spectroscopies and elemental analysis. The phase behaviour of these mesogenic compounds was characterized and studied by differential scanning calorimetry and polarizing optical microscopy. All the compounds 1a exhibited nematic (N) and/or smectic C (SmC) phases, as expected for rod-like molecules; however, the compounds 1b and 1c exhibited crystal phases. For those compounds 1a having shorter carbon chains (n = 1, 3, 4) nematic phases were observed, whereas for compounds having longer carbon chains (n = 6, 7, 8, 10, 12, 14) smectic C behaviour was also observed at lower temperatures. The greater aspect ratio (l/d) of compounds 1a compared with 1b and 1c was found to be required for the observation of liquid crystallinity. The fluorescent properties of these compounds were also examined. All λ_max peaks of the absorption and photoluminescence spectra of compounds 1a-1c occurred at c. 316-322 nm and 371-382 nm, respectively. The quantum yields of some compounds were relatively low, and also slightly solvent-dependent.     

Synthesis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols

Synthesis of (2R,3S,4S)-4-aryl-3-hydroxyprolinols has been established starting from 2-benzyloxymethylpyrrolidin-2-one framework, which is derived from commercially available trans-(2S,4R)-4-hydroxyproline. The single diastereomer having a trans–cis relative configuration with C₂ and C₃ and C₃ and C₄ is constructed in two one-pot functional group transformations of Grignard addition/dehydration and epoxidation/isomerization as the key steps in moderate yield.     

Tris-chelate complexes with chiral ligands: In search of diastereoisomeric selectivity with remote stereogenic centres

The chiral ligands, 4,4′-bis{(1S,2R,4S)-(−)-bornyloxy}-2,2′-bipyridine, (1S,2R,4S)-1, and 4,4′-bis{(1R,2S,4R)-(+)-bornyloxy}-2,2′-bipyridine, (1R,2S,4R)-1, have been prepared and characterized by spectroscopic techniques and, for (1S,2R,4S)-1, by single crystal X-ray diffraction. Despite the use of enantiomerically pure ligands, the formation of the complexes [Fe((1S,2R,4S)-1)₃]²⁺, [Ru((1S,2R,4S)-1)₃]²⁺, [Ru((1S,2R,4S)-1)(bpy)₂]²⁺ and [Ru((1R,2S,4R)-1)(bpy)₂]²⁺ proceeds without preference for either the Δ or Λ-diastereoisomers.     

Ferroelectric liquid crystal materials synthesized from 2(S)-[2(S)-methylbutyloxy]propanol

A new chiral alcohol, 2(S)-[2(S)-methylbutyloxy]propanol (3), containing two chiral centres has been synthesized from ethyl lactate and (S)-1-iodo-2-methylbutane. It was used as a chiral building block for the preparation of ferroelectric liquid crystal materials. Several of the new materials exhibit an enantiotropic S*_c phase with a wide temperature range. The results indicate that the molecular structure of 3 is useful for synthesizing ferroelectric liquid crystal materials.     

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1 ), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH₃, CH₃, OC₈H₁₇, C8H17, halogens, CF₃, OCF₃, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.     

Recent Progress in the Synthetic Applications of Substituted Furans and Pyrroles

In this lecture, I would like to present efficient synthetic routes towards the total synthesis of syringolide 1 (2)^1,2 and secosyrin 1 (3),¹ employing 2,4-disubstituted furan 1 as a common precursor. A modified total synthesis of prehispanolone (6)³ from (S)-(+)-Wieland-Miescher ketone (4) via hispanolone (5) will also be discussed. Our methodology for the synthesis of 3,4-disubstituted-lH-pyrroles⁴ and for the generation of 3,4-didehydrothiophene⁵ has also guided us to the successful identification of 1-tert-butoxycarbonyl-3,4-didehydro-1H-pyrrole (7),which is presumably the most strained heterocyclic cumulene ever recorded.     

Two new steroidal glycosides from Ophiopogon japonicus

Two new C27-steroidal glycosides were isolated from the fibrous roots of Ophiopogon japonicus. The spectral analysis and chemical evidence revealed their chemical structures to be （25R）-spirost-5,14-dien-3β-yl-O-α-L-rhamnopyranosyl-（1 → 2）-β-D- xylopyranosyl-（1 → 4）-β-D-glucopyranoside （1） and ophiogenin 3-O-β-D-glucopyranoside （2）.     

Stereoselective synthesis of (1R,2S)-2-amino-1,3-diols from (R)-cyanohydrins

Vinyl substituted (1R,2S)-amino alcohols 5 were obtained by addition of vinyl magnesium bromide to the corresponding cyanohydrin O-trimethylsilyl ethers (R)-2. The O- and N-protected vinyl amino alcohols 6 were ozonized at −78°C in methanol yielding (1R,2S)-2-amino-1,3-diols7 in high enantiomeric and diastereomeric excesses. For purification, compounds 7 in some cases were acetylated to give the derivatives (1R,2S)-8. Racemic 6a was converted by oxidative ozonolysis at −78°C in methanolic NaOH solution to the corresponding methyl N-acetyl-β-hydroxy propanoate 9a. The configuration of (1R,2S)-8a was confirmed by x-ray crystallographic analysis.     

The Total Synthesis of (±)-13-Hydroxyneocembrene

(13S)-hydroxyneocembrene(18), a cembranoid which was isolated in 1988 from soft coral Sarcophyton trocheliophorum¹, has been shown to be an effective inductor of the release of labeled glucose from the lecithincholesterol liposomes and have cytostatic activities². The geometrical structure and absolute configuration of 18 have been defined to be 1S, 2E, 7E, 11E, 13S. Herein, we report the total synthesis of (±)-13hydroxyneocembrene(18).     

Investigation of the crystal structure of two amphiphilic diols

The crystal and molecular structures of (R)-4'-(2,3-dihydroxypropyloxy)-4-cyanobiphenyl, 1 and 4'-(cis-cis-3,5-dihydroxycyclohexyloxy)-4-cyanobiphenyl, 5 have been determined. The packing of compound 1 occurs in sheets, with a dense hydrogen bonding network within the layer of one sheet and to the next sheet, whereby the cyano groups are incorporated into the hydrogen bonding network. The hydrogen bonding scheme of compound 5 involves a water molecule; there is some disorder with regard to the hydrogen atoms bound to the water molecules.