Through‐Bond/Through‐Space Anion Relay Chemistry Exploiting Vinylepoxides as Bifunctional Linchpins

The development of new bifunctional linchpins that permit the union of diverse building blocks is essential for the synthetic utility of anion relay chemistry (ARC). The design, synthesis, and validation of three vinylepoxide linchpins for through‐bond/through‐space ARC are now reported. For negative charge migration, this class of bifunctional linchpins employs initial through‐bond ARC by an S_N2′ reaction, followed by through‐space ARC exploiting a 1,4‐Brook rearrangement. The trans‐disubstituted vinylepoxide linchpin yields a mixture of E/Z isomers, whereas the cis‐disubstituted and the trans‐trisubstituted vinylepoxide linchpins proceed to deliver three‐component adducts with excellent E selectivity.     

Stereoselective syntheses of the C'D'E'F'-ring system of maitotoxin and the FG-ring system of gambierol

[structure: see text]. The stereoselective syntheses of the C'D'E'F'-ring system of maitotoxin and the FG-ring system of gambierol were accomplished. The key steps involve 6-endo-cyclization of methylepoxide, SmI2-induced reductive cyclization, 6-endo-cyclization of vinylepoxide, and formation of the lactone ring.     

Synthetic studies on maitotoxin. 2. Stereoselective synthesis of the WXYZA'-ring system

The stereoselective synthesis of the WXYZA'-ring system of maitotoxin has been accomplished via a linear synthetic approach, in which key reactions were SmI 2-induced cyclization of beta-alkoxyacrylate for the construction of the A'-, Y-, and X-rings and 6- endo cyclization of hydroxy vinylepoxide for that of the Z- and W-rings.     

Total synthesis of cristatic acid

The first total synthesis of cristatic acid 1, an antibiotic endowed with considerable activity against Gram-positive bacteria, hemolytic properties, and significant cytotoxicity, is described. Key to success are the formation of its 2,4-disubstituted furan moiety via a palladium-catalyzed alkylation of vinylepoxide 10 derived from sulfonium salt 8 and the use of SEM ethers as the protecting groups for the phenolic OH functions.     

Regio- and diastereoselective reductive coupling of vinylepoxides catalyzed by titanocene chloride

[reaction: see text] The Ti(III)-catalyzed reaction of a series of vinylepoxides leads, with regio- and E-diastereoselectivity control, to good-to-excellent yields of the corresponding homocoupling products. This homocoupling reaction, which involves a new C-C bond-forming method, takes place via a S(N)2' process between an allyltitanium species and the starting vinylepoxide. The process can be used for the rapid and efficient formation of highly valuable intermediates for organic synthesis, as well as new interesting homologues of natural products.     

四氟乙烯齐聚体的反应 四氟乙烯四、五聚体和芳香胺的反应

前已报道四氟乙烯四聚体(全氟-3,4-甲基己烯-3)(1)、五聚体(全氟-3,4-二甲基-4-乙基己烯-2)(2)和脂肪烷氧以及脂肪胺的亲核反应.本文报道化合物1,2和芳香胺如苯胺、β-萘胺的反应.由于烯烃1、2双键处于分子中间,因而当亲核试剂进攻时,双键容易发生重排,生成的末端基烯烃更具反应性,故导致一取代、二取代、三取代以及环化降解等复杂产物.     

Refolding foldamers: triazene-arylene oligomers that change shape with chemical stimuli

We describe the preparation of five triazene-arylene oligomers (3, 4, 7, 8, and 11) and investigations of their folding properties in aqueous solution. These oligomers contain four 2-fold rotors and populate a conformational ensemble comprising at least 10 states. Extensive 1D and 2D NMR studies as well as X-ray crystallography establish that the presence of three members of the cucurbit[n]uril family (CB[n]), CB[10], CB[7], and CB[8], results in the selective population of the (a,a,a,a)-, (a,s,s,a)-, and (a,a,a,s)-conformers. As a result of the high affinity and highly selective binding properties of the CB[n] family, it is possible to fold a single foldamer strand (3) into the CB[8].(a,a,a,s)-3 conformer by the addition of CB[8], then unfold and refold it into the CB[7].(a,s,s,a)-3.CB[7] conformer by addition of CB[7] and 3,5-dimethylaminoadamantane (17), then unfold and refold it again into the CB[10].(a,a,a,a)-3 conformer by addition of CB[10].CB[5] and aminoadamantane (18). The transformation of CB[8].(a,a,a,s)-3 into CB[7].(a,s,s,a)-3.CB[7] proceeds through the intermediacy of CB [8].(a,a,s,a)-3.CB[7], which enhances the rate of dissociation of strand 3 from CB[8].     

Electrophoresis of a sphere at an arbitrary position in a spherical cavity filled with Carreau fluid

Boundary effects on the electrophoretic behavior of a charged entity are of both fundamental and practical significance. Here, they are examined by considering the case where a sphere is at an arbitrary position in a spherical cavity under conditions of low surface potential and weak applied electrical field. Previous analyses are extended to the case of a non-Newtonian fluid, and a Carreau model is adopted for this purpose. The effects of key parameters such as the thickness of a double layer, the relative sizes of particle and cavity, the position of a particle, and the nature of a fluid on the electrophoretic mobility of a particle are discussed. Several interesting phenomena are observed. For example, if the applied electric field points toward north, the mobility of a particle has a local maximum when it is at the center of a cavity. However, if a particle is sufficiently close to the north pole of a cavity, its mobility exhibits a local minimum as its position varies. This does not occur when the particle is close to the south pole of the cavity; instead, it may move in the direction opposite to that of the applied electric field. For a Newtonian fluid, if a particle is close to the north pole of a cavity, its upward movement yields a clockwise (counterclockwise) vortex near the north pole of the cavity and a counterclockwise (clockwise) vortex near the south pole of the cavity on its right (left)-hand side. The latter is not observed for a Carreau fluid.     

Electrophoresis of a rigid sphere in a Carreau fluid normal to a large charged disk

The electrophoresis of a rigid sphere in a Carreau fluid normal to a large disk is analyzed theoretically under the conditions of low surface potential and weak applied electric field. Previous analyses are extended to the case where a disk can be charged, and a more realistic electrostatic force formula is applied. We show that the qualitative behavior of a sphere depends largely on its distance from a disk, the thickness of double layer, and the nature of a fluid. In general, the presence of a disk has the effect of increasing the conventional hydrodynamic drag on a sphere, and a decrease in the thickness of the double layer surrounding a sphere has the effect of enhancing the shear-thinning effect. However, this might not be the case if a sphere is uncharged and a disk is charged, where the osmotic pressure field and the induced charge on the sphere surface can be significant. The shear-thinning effect is important only if the thickness of double layer is sufficiently thick. This result can play a significant role in practice such as in electrophoretic deposition, where the deposition electrode is charged and the fluid medium is usually of shearing-thinning nature.     

Boron/nitrogen substitution of the central carbon atoms of the biphenalenyl diradical π dimer: a novel 2e-12c bond and large NLO responses

On the basis of the famous staggered biphenalenyl diradical π dimer 1, the eclipsed biphenalenyl (1a), with no centrosymmetry, was obtained by rotating a layer of 1 by 60° around its central axis. Furthermore, the central carbon atoms of 1 and 1a were substituted by boron and nitrogen atoms to form 2 and 2a with a novel 2e-12c bond. We found that the novel 2e-12c bond is formed by the electron pair of the occupied orbital of the phenalenyl monomer substituted by the nitrogen atom and the unoccupied orbital of the phenalenyl monomer substituted by the boron atom. As a result of the novel 2e-12c bond, 2 and 2a exhibit a fascinating interlayer charge-transfer transition character, which results in a significant difference in the dipole moments (Δμ) between the ground state and the crucial excited state. The values of Δμ for 2 and 2a are 6.4315 and 6.9253 Debye, clearly larger than the values of 0 and 0.0015 Debye for 1 and 1a. Significantly, the boron/nitrogen substitution effect can greatly enhance the first hyperpolarizabilities (β(0) ) of 2 and 2a with a novel 2e-12c bond compared with 1 and 1a with a traditional 2e-12c bond: 0 and 19 a.u. for 1 and 1a are much lower than 3516 and 12272 a.u. for 2 and 2a. Furthermore, the interaction energies (E(int) )of 2 and 2a are larger than those of 1 and 1a, which could be considered as a signature of reliability for the newly designed dimers. Our present work will be beneficial for further theoretical and experimental studies on the properties of molecules with the novel 2e-12c bond.     

Functionalized chloroenamines in aminocyclopropane synthesis - VI. Chlorotetrahydropyridines as a basis for the synthesis of 3-azabicyclo[3.1.0.]hexane derivatives

Enamines 8a-e could be chlorinated by equimolar amounts of N-chlorosuccinimide (9) generating monochloroenamines 10a-e; 10a and 10d were isolated as pure substances. Two equivalents of 9 afforded the dichloroenamines 12a,c from 8a,c. Interaction of the chlorinated enamines 10a-e and 12a,c with cyanide gave morpholino-azabicyclohexane derivatives. 10a-d, thereby, led to exo-cyano-isomers lla-c; 12a,c generated endo-cyano compounds 13a,c. In the case of the ethoxycarbonylated chloroenamine 10e a mixture of diastereomeric products 11e and 14e resulted from the analogous reaction. Reduction of 11a and 14e with lithium aluminum hydride produced a pair of diastereomeric triamines 15 and 16. A tricyclic diazasystem 19 was formed from the reaction of cyanide with the carbamoylated chloroenamine 18. Monochloroenamine 10a and dichloroenamine 12a showed a significant mutagenic behaviour in the Ames test.     

Fatty acids. II. The synthesis and gas-liquid chromatographic behaviour of five trimethylene-interrupted C18-diunsaturated fatty acids.

Five trimethylene-interrupted methyl octadecadiynoates, C18 delta-2a,-7a; delta-3a,-8a; delta-4a,-9a; delta-5a,-10a and delta-6a,-11a, and the corresponding cis,cis-octadecadienoates were synthesized, and their gas-liquid chromatographic properties were studied on Apiezon L, diethylene glycol succinate polyester and Silac 10C stationary phases. The equivalent chain lengths of these esters have been determined, and the separation of mixtures and the prediction of gas chromatographic behaviour of these isomers are discussed.     

One-pot synthesis of metalated pyridines from two acetylenes, a nitrile, and a titanium(II) alkoxide

Four-component coupling process involving two acetylenes, a nitrile, and a divalent titanium alkoxide reagent, Ti(O-i-Pr)(4)/2i-PrMgCl, directly yielded titanated pyridines in a highly selective manner. The reaction can be classified into four categories: (i) a combination of an internal acetylene, a terminal acetylene, sulfonylnitrile, and the titanium reagent to yield alpha-titanated pyridines, (ii) a combination of an internal acetylene, a (sulfonylamino)acetylene, a nitrile, and the titanium reagent to yield alternative alpha-titanated pyridines, (iii) a combination of an internal acetylene, a (sulfonylamino)acetylene, a nitrile, and the titanium reagent to yield titanated aminopyridines, and (iv) a combination of an acetylenic amide, a terminal acetylene, a nitrile, and the titanium reagent to yield pyridineamides with their side chain titanated. Some of these reactions enabled virtually completely regioselective coupling of two different, unsymmetrical acetylenes and a nitrile to form a single pyridine. Synthetic applications of these reactions have been illustrated in the preparation of optically active pyridines and medicinally useful compounds.     

Synthesis, properties, and redox behavior of di(1-azulenyl)(2- and 3-thienyl)methyl cations and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thienothiophenediyl spacers

The titled stable monocations, di(1-azulenyl)(2- and 3-thienyl)methyl cations 7a,b and 8a,b and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thieno[3,2-b]thiophenediyl spacers 9a,b and 10a,b were prepared by hydride abstraction of the corresponding methane derivatives. These mono- and dications 7a,b, 8a,b, 9a,b, and 10a,b showed high stability with large pK(R)+ values. The values of monocations 7a,b and 8a,b were 11.2-11.8 +/- 0.1 and 11.4-12.4 +/- 0.1, respectively. Two cation units in dications 9a,b and 10a,b were neutralized via one step at the pH of 11.1-11.7 +/- 0.1, which corresponds to the average of the pK(R)+ values of the dications and half-neutralized monocations. Electrochemical behavior of 7a,b, 8a,b, 9a,b, and 10a,b was examined by cyclic voltammetry (CV). Formation of the thienoquinoid products 18a,b and 19a,b from 9a,b and 10a,b was characterized by UV-vis spectroscopy under electrochemical reduction conditions. Chemical reduction of 9a,b and 10a,b with Zn powder in acetonitrile afforded 18a,b and 19a,b as deep-colored crystals, which exhibited rather high electron-donating ability.     

Density functional theoretical study on enantiomerization of 2,2'-biphenol

The S-R enantiomerization processes of 2,2'-biphenol (biphenol) have been investigated using density functional theory (DFT). Five isomers for biphenol were identified: I0, which is the most stable isomer; I1a and I1b, which are formed by a restricted rotation of one OH group; and I2a and I2b, which are formed by a restricted rotation of the two OH groups where a and b denote cis and trans configurations, respectively. Each isomer has R- and S-enantiomers. The energies relative to the most stable isomer I0 are 1.6, 3.3, 5.3, and 5.5 kcal mol(-1) for I1a, I1b, I2a, and I2b, respectively. The direct enantiomerization of I0, in which the phenol-ring rotation is considered to be the reaction coordinate while the OH rotations are frozen, is forbidden because of the repulsion between the two OH groups. The transition states for isomerizations of I0 to other isomers (I1a, I1b, I2a, or I2b) were calculated as well as those for the other direct enantiomerizations except for that of I0. From the viewpoint of the least number of the transition states and their low energy levels, the probable S-R enantiomerization of I0 is expressed as a sequential process of isomerization: I0,S --> I1a,S, a direct enantiomerization induced by one of the two OH rotations, I1a,S --> I1a,R, and another isomerization, I1a,R --> I0,R, that is, I0,S --> I1a,S --> I1a,R --> I0,R as the whole process. This process is effective in quantum control of the enantiomerization of biphenol and can be carried out by a sequence of a pump-dump IR laser-pulse scheme.     

Photochemische Umwandlungen, 45. Mitteilung [1] die 3σ → 3π-route zu oxepin-derivaten

Exemplifying with the 4.5-dicarbomethoxy oxepin 6a the authors describe an oxepin synthesis from furanes and acetylenic dienophiles via Diels-Alder reaction ( 4a ), photochemical oxanorbornadiene-oxaquadricyclane transformation ( 4a → 5a ), and thermal 3σ → 3π opening of the highly strained oxaquadricyclane 5a . With dimethylacetylenedicarboxylate, methylpropiolate, maleic anhydride, and di-methoxycarbonyl-oxanorbornadiene ( 4a ) 5a yields the 1:1 adducts 19a, 19b, 22, 23 and 26 (unstable) by strictly stereospecific addition to the α-positions of the oxygen bridge. With the same dienophiles the oxepin 6a reacts only through its valence-tautomeric benzene-oxide form 7a giving stereospecifically 27, 29, 30 and 31 . No definite conclusions are drawn with regard to the mechanistic implications of the photostep 4a → 5a , the thermal 3σ → 3π-transformation 5a → 6a/7a , and the bishomofurane cycloaddition reactions. Scope and limitations of this oxepin synthesis are briefly discussed.     

Crystal engineering of photochromic diarylethene single crystals

Photochromic performance of diarylethene single crystals was controlled by crystal engineering using non-covalent aromatic-aromatic interactions as the directional intermolecular force. A diarylethene derivative with two pentafluorophenyl groups, 1,2-bis(2-methyl-5-pentafluorophenyl-3-thienyl)perfluorocyclopentene (1a), formed stoichiometric co-crystals with benzene (Bz) and naphthalene (Np) by aryl-perfluoroaryl interactions. Face-to-face pi-stacking interactions between the pentafluorophenyl groups of 1a and the aromatic molecules are responsible for 2:1 and 1:1 stoichiometric compositions in 1a/Bz and 1a/Np co-crystals, respectively. The diarylethene underwent thermally stable and photoreversible photochromic reactions in a homo-crystal of 1a and co-crystals 1a/Bz and 1a/Np. The absorption spectra of the photogenerated closed-ring isomers varied depending on the conformation of the diarylethene molecules packed in the crystals. The diarylethene 1a also formed 1:1 stoichiometric co-crystals with different kinds of diarylethenes, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis[2-methyl-5-(1-naphthyl)-3-thienyl]perfluorocyclopentene (3a). Both co-crystals 1a/2a and 1a/3a showed photochromism. Although 1a, 2a, and 3a underwent efficient photocyclization reactions in their homo-crystals, highly selective photocyclization reactions of 2a or 3a were observed in the co-crystals. The selective reactions were confirmed by HPLC and X-ray crystallography. Excited energy transfers from 1a to 2a and from 1a to 3a are considered to occur and cause the selective reactions.     

Structural characterization and chemical response of a Ag-coordinated supramolecular gel

Supramolecular gels exhibit potential applications in the areas of sensors, nanodevices, drug and catalyst carriers, and so on. To develop a novel organogel with a multiresponse, we designed a component molecule bearing a pyridyl group for metal coordination and an amide group for the formation of intermolecular hydrogen bonding. A complex building block with a symmetrical structure was selectively constructed by the coordination of a silver cation to the organic component. The coordination existing in the complex and the hydrogen bonding existing between complexes were examined by IR, Raman, and 1H NMR spectroscopy. The gel formation and phase transition were examined by viscosity and differential scanning calorimetry measurements. The selection of metal ions for the formation of a gel has proved to be crucial as only the complex of a binary coordinated metal ion, Ag+, was found to form a gel structure. From the band shift of the L1 solution with different amounts of silver ion, the binding ratio of silver ion to L1 was estimated to be 1:2 and the calculated stability constant was 3.6 x 10(8) M(-2). On the basis of the analysis of X-ray diffraction and transmission electron microscopy results, we proposed a possible stacking structure of the complex in the fibrous aggregates. Of interest is that the organogel exhibits a 3-D network structure of a beltlike fiber composed of ordered lamellar arrangements of the coordinated complex and shows a rapid response to wide chemical stimulations such as anions I-, Br-, and Cl-, gases such as H(2)S and NH(3), and a change of pH.     

Morphology of spinodal decompositions in liquid crystal-colloid mixtures

We study the morphology of spinodal decompositions (SDs) in mixtures of a liquid crystal and a colloidal particle by solving time-dependent Landau-Ginzburg equations for a conserved order parameter (concentration) and two nonconserved order parameters (orientation and crystallization). We numerically examine the coupling between concentration, nematic ordering, and crystalline ordering in two dimensional fluid mixtures, coexisting a nematic and a crystalline phase. On increasing the concentration of colloidal particles, we have three different SDs: a nematic order-induced SD, a phase-separation-induced SD (PSD), and a crystalline-order-induced SD (CSD). In NSD, the phase ordering can lead to fibrillar and cellular networks of the minority colloidal-particle-rich phase in early stages. In the PSD, we find a bicontinuous network structure consisting of a nematic phase rich in liquid crystal and a crystalline phase rich in colloidal particles. In the CSD, nematic droplets can be formed in a crystalline matrix. Asymmetric mixtures of a liquid crystal and a colloidal particle lead to rich varieties of morphologies.     

Photochromic reactions of diarylethenes in single crystals with intermolecular O--H...N hydrogen-bonding networks

The crystal structures and photochromic performance of a single crystal of a diarylethene derivative possessing carboxyl groups, 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (1 a), and cocrystals of 1 a with 4,4'-, 2,4'-, and 2,2'-bipyridines were examined. In crystal 1 a, a discrete cyclic structure was observed, in which four 1 a molecules are linked through hydrogen bonds between the carboxyl groups. In the homocrystal, photoreactive and photoinactive conformers of 1 a exist in the ratio of 1:1. In the cocrystals of 1 a with bipyridines, O--HN-type hydrogen bonds between 1 a and pyridyl groups were formed, and all 1 a molecules are fixed in a photoreactive conformation. Both the homocrystal 1 a and the cocrystals showed photochromic performances, and color variation from bluish-violet to cyan was observed, depending on the conformation of the packed diarylethene molecules.