Search

Blue phases (BPs) obtained by doping a commercially available liquid crystalline compound (4-butyl-N-(4-ethoxybenzylidene)aniline (EBBA)) with (2R,3R)-2,3-bis(4-octyloxyphenylbenzoyloxy)-N-(hydroxydecyl)succinimide (1) were highly stabilised by the addition of a small amount of alkane diols. Especially, addition of only 0.5 mol% of octane-1,8-diol increased the BP–Iso transition temperature by 10 K and widened the BP temperature range up to 35 K. A model stabilisation mechanism based on the construction of a hydrogen bond network in each disclination zone in BPs was proposed.

Blue phases (BPs) have received considerable attention as light shutters in the next generation of liquid crystal (LC) displays. However, no simple and efficient chiral dopant for induction of BPs of commercially available rodlike LC compounds has been reported. In this study, both (R) and (S) forms of novel chiral dopants were synthesized, showed extremely high helical twisting power values in nematic LC compounds, and induced stable BPs with a small amount of our chiral dopants (3-5 mol %). In enantiomeric excess controlled experiments, we found novel phenomena in their physical properties, such as generation of a metastable chiral nematic phase between an isotropic state and a BP.

Novel C2-symmetric chiral dopant derivatives, namely, N-substituted (2R, 3R)-2,3-bis(4-(4-octyloxyphenyl)benzoyloxy)succinimides1a-h, were synthesised, and the effects of the N-substituent and imide-carbonyl groups on the helical twisting powers (HTPs) were investigated in two nematic liquid crystalline compounds, 4-n-pentyl-4ʹ-cyanobiphenyl (5CB) and N-(4-ethoxybenzylidene)-4-n-butylaniline (EBBA). As a result, it was clarified that the bulkiness of the N-substituents has a significant correlation with the HTPs, and the imide-carbonyl group interacts strongly with the cyano group of 5CB to give high HTPs in the nematic phases. However, it is assumed that the imide-carbonyl groups of the dopants do not have strong electrostatic attractive interactions with EBBA molecules in the nematic phase to afford the moderate HTPs.

Aromatic chain imides possessing chromophores connected by iminodicarbonyl linkers were synthesized as novel aromatic foldamers. In these molecules chromophores face each other and form the helical folding structures both in solution and in solid state. Their folding structures were investigated by single crystal X-ray analysis and 1H NMR spectroscopy. A circular dichroism (CD) spectral study on the chiral aromatic chain imides with bulky N-substituents showed that their helically chiral conformation based on folding remained for a reasonably long time without racemization in solution. As the number of folded chromophores increased, their absorption and fluorescence spectra were red-shifted, and induced CD signals were increased. This remarkable change is based on the intramolecular interaction between folded chromophores. As an application of these aromatic chain imides, a chiral photochromic system was investigated by utilizing the intramolecular photo [4+4] cycloaddition and thermal cycloreversion of anthracene and naphthalene chromophores connected by iminodicarbonyl linkers.

[structure: see text] Carboxamides possessing naphthalene rings connected by multiple iminodicarbonyl linkers were synthesized. These molecules forced the naphthalene rings to be placed in the positions facing each other, and they form helical foldamers both in solution and in the crystalline state. Their folding structures were investigated by single-crystal X-ray analysis and (1)H NMR spectroscopy. Their absorption and fluorescence spectra showed a red shift as the number of naphthalene moieties increased. This remarkable change is based on the intramolecular interaction between naphthalene moieties. Helicity of the foldamer can be controlled by the introduction of chiral auxiliaries at imide nitrogen atoms, which results in an observation of induced circular dichroism.

Previously we reported regioselective formation of dianions derived from liner nitroalkanes in the presence of n-BuLi and HMPA. The formation of nitroalkane dianions either α,α- or α,β-dianions depended on the order of addition of reagents. However, the usage of a carcinogen suspected compound like HMPA is undesirable. Therefore we re-investigated the new combination of bases and aprotic dipolar solvents other than HMPA. After exploration of a variety of their combination, it was found that the combination of LDA and DMPU resulted in the formation of α,β-dianion with the best regioselectivity; the ratio of α- to β-adduct was 1 to 14 in the reaction of nitroethane with benzaldehyde.

The photocycloaddition reaction of naphthyl-N-(naphthylcarbonyl)carboxamides (1) was examined under argon and oxygen atmospheres. In addition to the [2 + 2] and [4 + 4] cycloadducts, 3 and 4, respectively, novel 1,8-epidioxides (5) were formed under oxygen atmosphere. The transient absorption at lambda max of 360 nm with the lifetime of 360 ns was observed by laser flash photolysis of 1c and was interpreted as the absorption of biradical intermediate 2. On the basis of the anti stereochemistry of 5, which was different from that of the major [4 + 4] cycloadducts, syn-4, it was deduced that equilibrium between biradical intermediates syn-2 and anti-2 would exist. Retro [2 + 2] cycloaddition of 3 was responsible for the efficient trapping of the biradical intermediate with molecular oxygen. The photocycloaddition of the anthryl derivatives, 9-anthryl-N-(methylethyl)-N-(naphthylcarbonyl)carboxamides (7), afforded the [4 + 4] cycloadducts (8) exclusively in a quantitative yield even under oxygen atmosphere. The absence of trapping with molecular oxygen was interpreted to be due to the lack of retro [4 + 4] cycloaddition of 8.

A novel clathrate host, N,N‘-bis(2-tert-butylphenyl)pyromellitic diimide (1), was designed to create a sandwich structure without using cyclophanes nor the acyclic compounds. In the host−guest crystal, the host molecule is sandwiched between two aromatic guest molecules. The inclusion experiment was performed by recrystallization of 1 from chloroform in the presence of the guest at room temperature to give the clathrate compounds. Phenols (phenol, p-cresol, α-naphthol, β-naphthol, catechol) and indoles (indole, 3-methylindole, 4-methylindole, 5-methylindole) were included in the clathrate compounds, and the host/guest ratio 1:2 was observed in all cases. To explain the mechanism of the self-assembly to the piled sandwich structure, X-ray analysis of the single crystals was performed in all cases. Further, charge-transfer complexation, hydrogen bonding and dipole−dipole interaction were investigated using UV, IR, differential scanning calorimertry (DSC), and AM1 calculation. The order of the decomposition ...

Novel poly[S-alkylcarbamate]s were prepared by polyaddition of oligo [2,5-bis(thiomethyl)-1,4-dithiane] (oligo[BMMD]) with isocyanate for optical polymers having high refractive indices (nD) and Abbe's numbers (νD). Oxidation of 2,5-bis(mercaptomethyl)-1,4-dithiane (BMMD) with ferric chloride or methylsulfoxide gave oligo[BMMD] in a mixture of n-mers (typically n = 1−6) by disulfide-forming propagation. The use of the former oxidant giving mainly BMMD dimer appeared to be preferable for the subsequent preparation of transparent poly[S-alkylcarbamate]. With 1,3-bis(isocyanatomethyl)cyclohexane, 1,6-diisocyanatohexane, or 1,3,5-tris(isocyanatomethyl)cyclohexane, nD:νD values of poly[S-alkylcarbamate]s ranging from 1.609:38.0 to 1.659:35.6 were comparable to those of flint glasses. Copoly[S-alkylcarbamate]s were prepared using 2-mercaptoethylsulfide or 2-mercaptoethylether for modification of nD and νD. Contribution of the disulfide bond and the 1,4-dithiane ring in oligo[BMMD] to increase nD is discussed in terms of molar refraction. Suppressed UV absorption of the polymer, which caused high νD, was attributed to the trans-gauche-trans conformation around the disulfide bond. This work shows that oligo[BMMD] serves as a useful material for the preparation of polymers having high nD and high νD and that poly[S-alkylcarbamate]s thus obtained are promising optical materials.

A mild and convenient method for generation of nitrile oxide is established by iodosylbenzene oxidation of aldehyde oximes. Aldehyde oximes were converted to furoxans in almost quantitative yields via dimerization of corresponding nitrile oxides upon oxidation. When the oxidation was carried out in the presence of alkene and alkyne dipolarophiles, isoxazolines or isoxazoles were obtained in good yields.

Recent studies on intramolecular epoxide cyclizations were reviewed. Regio- and stereoselective anionic cyclization of epoxy-nitriles, -olefins, -carbamates and -alcohols were discussed. Also regio- and stereoselective Lewis acid promoted epoxide cyclizations, radical and paradium-catalyzed ones were described.

The first tandem radical cyclization of linear homoallylic xanthates was explored. Homoallylic santhates prepared from α,β-unsaturated esters were easily cyclized by tin hydride with an radical initiator to give the corresponding thionolactone annulated cyclopentane skeleton in a high yield. The stereochemistry of cyclized products was also discussed. Thionolactones obtained were oxidized chemoselectivity with m-CPBA under neutral condition to afford γ-lactones in a high yield

Octahomotetraoxacalix[4]arenes bearing long alkyl chains on their lower rim were prepared. Ester 4a existed in a 1,2-alternate conformation in its crystal structure, which was examined by single-crystal X-ray diffraction analysis. To prepare liquid crystalline materials possessing calixarene moieties by self-assembling, carboxylic acid derivatives 5 were synthesized. Among them, 5c, the octadecyloxy derivative, showed smectic liquid crystal phase. Homooxacalixarenes 5 also formed liquid crystal phases with longer layer distances when two equivalent moles of 1,2-ethylenediamine were added as a linker. These phases were investigated with X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy.

Conformational control of a cyclophane with intermolecular hydrogen bonding was accomplished through the first synthesis of a carbamoyloxa-bridged cyclophane 3, with the result that the crystal structures of two isolable conformers 3a and 3b were elucidated to be anti-(E,E) and anti-(Z,Z) by X-ray analysis. The convenient conversion of 3a to 3b was carried out with hydrogen bonding assisted by polar solvents

A mild and convenient method for generation of nitrile oxides is established by dimethyldioxirane oxidation of aldehyde oximes. Aldehyde oximes were converted to furoxanes in almost quantitative yields via dimerization of the corresponding nitrile oxides upon oxidation. When the oxidation was carried out in the presence of alkene or alkyne dipolarphiles, isoxazolines or isoxazoles were obtained.

The aldol reaction of the boron enolate bearing the titled chiral auxiliary proceeded with high face selectivity.

Irradiation of aromatic carbonyl compounds in hexamethylphosphoric triamide (HMPA) resulted in the cross-coupling of ketyl radicals with the HMPA-derived radical generated via hydrogen abstraction from it. The results on acetolysis, methanolysis, and the reaction with thionyl chloride of the resulting coupling products are described.

The crystal structures of two aromatic chain imides, N-(naphthyl)-N-benzyl-9-phenanthylcarboxamide (1) and N-(9-anthrylcarbonyl)-N-{12-[9-anthryl-N-(phenylcarbonyl)carbonylamino]dodecyl}benzamide (2), were examined. In both imides, two aromatic moieties face each other, creating concave-shaped conformations.

Recent Studies on regio- and stereoselective synthesis using transmetallation reaction of organotin compounds were reviewed.Regioselective 1, 4-dianion formations and its rearrangements, [2, 3] -sigmatropic rearrangements of allylic lithiomethyl ether and its applications to the chiral transfer reaction of steroidal side-chain, and transmetallaion of α-alkoxystannyl compounds with retention of configuration were discussed. Some applications to the total synthesis of natural products were also described.

直鎖ニトロアルカンジアニオンと求電子試薬とのアルドール付加反応ではニトロ基のα-位炭素上での炭素-炭素結合形成反応が報告されている。α,α-ジアニオンからα,β-ジアニオンへの位置選択性を試薬の滴下順序を変えることにまり制御しうることを見いだした。HMPAとニトロァルカンのTHF溶液にn-BuLiを加える:A法)ではα-付加物が得られる。ところがHMPAとn-BuLiのTHF鴇溶液にニトロアルカンを加える:B法)ではβ一付加物が優位に得られた。典型的な例としてニトロエタンジアニオンとベンズアルデヒドとの反応で,A法ではβ-付和物(1-フェニル-3-ニトロ-1-プロパノール)の生成が14%であった。これに反しでB法(HMPA/n-BuLi=2.6:1のモル比,ニトロエタンを-90℃で加えた)ではβ-付加物の相対収率が95%と極めて高選択的であり,しかも高収率であった。この反応ではHMPA/n-BuLiのモル比がα-およびβ-付加物の生成を制御していることを示した。さらにいくつかの求電子試薬との反応でも高選択的にB法によりβ-付加物を得た。

A new method for the preparation of (Z)-4-alkylidenebutenolides is described. Coupling reaction of acetylenic stannanes with enol triflates of β-keto esters gave the corres ponding (Z)-2-alken-4-ynoates which were hydrolyzed and then subjected to cyclization in the presence of HgO to give moderate yields of (Z)-4-alkylidenebutenolides.

Isolement et caracterisation d'une toxine a proprietes antitumorales, a partir d'une eponge de l'espece Dragmacidon. Pour caracteriser cette nouvelle molecule appelee Dragmacidine, les techniques classiques d'investigation ont ete utilisees: Spectrometrie RMN, IR, UV… Des essais de toxicite sur des cellules leucemiques de souris ont ete effectues in vitro

A Sommelet–Hauser rearrangement of sulfonium ylides of 4H-pyran-4-ones, furan, and thiophenes are discussed. The sulfonium halides which were prepared from excess dimethyl sulfide with corresponding halides were treated with NaH or NaOR in a polar solvent to give moderate to good yields of rearranged products.

1,1-Dimethyl-5,6-dihydroxyindolinium chloride (1a)was identified from a deep water sample of the marine sponge,Dercitus sp., and its structure was elucidated by spectral methods.