Practical designed syntheses of all stereoisomeric bis(2,2')- and tris(2,2',2' ')-tetrahydrofurans

A convenient synthetic entry to the entire group of bis(2,2')- and tris(2,2',2' ')-tetrahydrofurans has been developed. The method is concise and relies on chromatographic separation, decarbonylation, and annulation to arrive at a specific product of defined relative configuration. [reaction: see text]     

Molecular weight dependent charge carrier mobility in poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene)

Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.     

Two-photon absorption properties of iron(II) and ruthenium(II) trischelate complexes of 2,2':4,4' ':4',4' '-quaterpyridinium ligands

A series of RuII or FeII trischelate complex salts containing N-methyl/aryl-2,2':4,4' ':4',4' '-quaterpyridinium ligands that has previously been subjected to quadratic nonlinear optical studies (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 13399) has now been investigated for two-photon absorbing behavior. Z-scan measurements using a 750 nm laser afford reasonably large two-photon absorption (2PA) cross-sections sigma2 of ca. 62-180 GM for the RuII complexes, but only very weak 2PA is observed for the FeII compounds. The excited-state and 2PA properties of the representative chromophore [RuII(Me2Qpy2+)3]8+ (Me2Qpy2+=N' ',N' '-dimethyl-2,2':4,4' ':4',4' '-quaterpyridinium) have also been investigated by using semiempirical intermediate neglect of differential overlap/multireference-determinant single and double configuration interaction computations with the optimized geometry obtained via density functional theory. The calculated sigma2 value of ca. 624 GM at 1.70 eV for this metal-to-ligand charge-transfer chromophore is about 10 times larger than that obtained from the Z-scan studies.     

Ligand substituent effect observed for ytterbocene 4'-cyano-2,2':6',2' '-terpyridine

A new N-heterocyclic complex of ytterbocene (Cp(2)Yb(II), Cp = C(5)Me(5)) has been prepared by the addition of 4'-cyano-2,2':6',2' '-terpyridine (tpyCN) to Cp(2)Yb(II)(OEt(2)) in toluene to give a dark blue species designated as Cp(2)Yb(tpyCN). The effect of the electron-withdrawing group (-CN) on the redox potentials of the charge-transfer form of this complex [in which an electron is transferred from the f(14) metal center to the lowest unoccupied (pi) molecular orbital of the tpyCN ligand to give a 4f(13)-pi(1) electronic configuration] has been quantified by cyclic voltammetry. The tpyCN ligand stabilizes this configuration by 60 mV more than that in the unsubstituted tpy ligand complex and by 110 mV more than that in the unsubstituted bpy ligand complex. Magnetic susceptibility measurements corroborate the enhanced stabilization of the 4f(13)-pi(1) configuration by the substituted terpyridyl ligand complex. Furthermore, the temperature dependence of the magnetic data is most consistent with a thermally induced valence tautomeric equilibrium between this paramagnetic 4f(13)-pi(1) form that dominates near room temperature and the diamagnetic 4f(14)-pi(0) form that dominates at low temperature. Differing coordination modes for the tpyCN ligand to the ytterbocene center have also been confirmed by isolation and X-ray crystallographic characterization of complexes binding through either the cyano nitrogen of tpyCN or the three terpyridyl nitrogen atoms of tpyCN.     

Efficient synthesis of a new structural phenanthro[9,10,3',4']indolizidine starting from pyrrole

A new structural phenanthroindolizidine, 2,3,6,7-tetramethoxyphenanthro[9,10,3',4']indolizidine, has been synthesized efficiently from pyrrole. An important feature of this synthesis is that intramolecular oxidative coupling and rearrangement of 6,7-bis(3,4-dimethoxyphenyl)-8-methoxy-1,2,3-trihydroindolizin-5-one by using VOF3 and TFA have been achieved in one pot.     

A highly enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene catalyzed by chiral titanium(IV) 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol complexes

The catalytic effect of chiral Lewis acids on the hetero-Diels-Alder reaction between aldehydes and Danishefsky's diene (1) has been investigated. A variety of combinations of different ligands and Lewis acids have been examined as catalysts for the hetero-Diels-Alder reaction between benzaldehyde and 1, and it has been found that the readily accessible Ti(IV)-H(8)-BINOL (TiHBOL) complex is a very effective catalyst for the reaction, leading to products with very high enantioselectivity (up to 99% ee) and yield (92%). The hetero-Diels-Alder reaction of other aldehydes with 1 under the catalysis of TiHBOL is a general reaction which proceeds well with very high enantioselectivity and isolated yield for various aldehydes at 0 degrees C to room temperature. Based on the experimental results, the proposed mechanism of the hetero-Diels-Alder reaction and the dihedral angle effects of ligands are discussed.     

Rigid pi-conjugated mono-, bis-, and tris(2,2':6',2' '-terpyridines)

A set of rigid, pi-conjugated linear mono- and bisterpyridines and star-shaped tristerpyridines have been synthesized using Pd(0)-catalyzed coupling reactions and the Horner-Wadsworth-Emmons reaction. The terpyridyl ligands obtained feature strong emission in the blue range with high quantum yields in dilute solution and thin films.     

14-羟基菲并[9,10,3’,4’]吲哚里西啶的合成及生物活性研究

以吡咯为起始原料, 以三氟氧钒(VOF3)氧化偶联重排反应为关键步骤, 经过7步反应, 合成了结构骨架全新的14-羟基菲并[9,10,3’,4’]吲哚里西啶化合物8, 总收率为55%. 采用1H NMR, 13C NMR, IR, MS和HRMS对中间体和目标产物进行了表征. 初步的抗烟草花叶病毒生物活性测试结果表明, 目标化合物8对烟草花叶病毒无明显抑制作用, 但具有较好的抗肿瘤活性, 中间体9-氧代-14-羟基-14a-甲氧基菲并[9,10,3’,4’]吲哚里西啶化合物7却表现出了很好的抗烟草花叶病毒活性.     

Orientational control of electronic coupling in mixed-valence, binuclear ruthenium(II)-bis(2,2':6',2' '-terpyridine) complexes

A series of binuclear ruthenium(II)-bis(2,2':6',2' '-terpyridine) complexes has been prepared around a central biphenylene unit equipped with a strap of variable length. Partial oxidation forms the mixed-valence complex that displays both ligand-to-metal, charge-transfer, and intervalence charge-transfer (IVCT) transitions in the near-IR region. On the basis of Hush theory, the electronic coupling matrix element for interaction between the metal centers decreases with increasing length of the tethering strap. This effect arises because the strap modulates the torsion angle between the phenyl rings and thereby controls the extent of through-bond electronic coupling. The coupling element favors a maximum for planar geometries and a minimum for orthogonal structures, but the full impact of the torsion angle is not realized due to thermal fluctuations.     

A Novel Stereoselective Synthesis of 8-O-4' Neolignans

1-(4-hydroxy-3-methoxyphenyl)-2-(4-formyl-2-methoxyphenoxy)-propane-1,3-diol 9, a natural 8-O-4' neolignan, was isolated as a mixture of erythro and threo isomers from wood of Larix leptolesis1. This kind of neolignans have shown various biological activities2-4.As reported previously, the synthesis of 8-O-4' neolignans was mainly achieved using oxidative coupling of monolignols4,5 and reduction of ketones which were prepared from bromoketone and phenols in basic conditions6, But these method…     

Synthesis (and alternative proof of configuration) of the scyphostatin C(1')-C(20') trienoyl fragment

[reaction--see text] Each of four diastereomers of structure 2, corresponding to the lipophilic side chain of scyphostatin (1), were prepared. Careful analysis of their NMR spectral data and comparison with those of the natural product corroborates the recently reported (Org. Lett. 2000, 2, 505) stereochemical assignment. A strategy for the stereoselective synthesis of 2 has been achieved.     

Synthesis, X-ray structure, and self-assembly of functionalized bis(2,2':6',2' '-terpyridinyl)arenes

meta-Bis(terpyridinyl)phenol has been synthesized from O-benzyl-3,5-di(formyl)phenol in three steps. Its alkylation afforded a series of bisterpyridinylarenes, which can be self-assembled to afford the corresponding hexametallomacrocycles possessing Fe(II), Zn(II), or Ru(II) connectivity. [structure: see text]     

Synthesis of (2S,3R)-[3',3',3'-2H3]-valine and (2S,3S)-4-fluorovaline

A new synthesis of (2S,3R)-[3',3',3'-2H3]-valine has been completed and (2S,3S)-4-fluorovaline has been synthesised for the first time. Both compounds have been prepared by routes involving stereoselective addition to the (S)-pyroglutamate derivative and are available for studies in several areas of bio-organic chemistry.     

Dipyrrolo[1,2-a;2':,1'-c]pyrazines. 7. Electrophilic Substitution of Dipyrrolo[1,2-a;2',1'-c]pyrazines and 5,6-Dihydrodipyrrolo[1,2-a;2',1'-c]pyrazines via Formylation of Dipyrrolo[1,2-a;2':,1'-c]pyrazines

A series of previously unreported aldehydes has been prepared by the formylation reaction of dipyrrolo[1,2-a;2':,1'-c]pyrazines and their 5,6-dihydro analogs by DMF and phosphorus oxychloride.     

Total synthesis of 3',5'-C-branched nucleosides

[reaction: see text] A novel total synthesis of 3',5'-C-branched uridine azido acid has been accomplished using stereoselective aldehyde alkynylation, Ireland-Claisen rearrangement, and iodolactonization as the key reactions. Compared to traditional routes that start from carbohydrates, the present methodology is more efficient, flexible for future optimization, and provides access to both enantiomers of the products. Because the key chemistry does not involve the 3'- and 5'-C substituents, our route is a general approach to 3',5'-C alkyl nucleoside analogues.     

Fused Diazepines. Synthesis of 2-Methyl-8-aryl-4,6-dihydro-5H-thieno[3',2':4,5]thieno[2,3-d][1,2]diazepin-5-ones

Russian Journal of Organic Chemistry - Heterocyclization of ethyl 2-acetyl(aroyl)-5-methylthieno[2,3-b]thiophene-3-acetates with hydrazine hydrate has been studied. A dependence of the reaction...     

Synthesis and mesomorphic properties of 4-methoxyphenyl 4'- n -alkoxy-2',3',5',6'-tetrafluorobiphenyl-1-carboxylates

A novel type of 4-methoxyphenyl 4'- n -alkoxy-2',3',5',6'-tetrafluorobiphenyl-1-carboxylates have been synthesized. Textural observations by polarizing microscopy and DSC measurements of the phase transitions show that all of these compounds are thermotropic liquid crystals with only a nematic mesophase. The relationship between the properties and chemical structures of these compounds is discussed.     

A novel method of preparing amine-modifying C-4' oxidized nucleotide

A novel method of preparing C-4' oxidized nucleotide, a monomeric model of an alkali labile lesion (1) has been studied. The C-4' selenated 4a and 4b were found to be effective in preparing 3, a monomeric model of 1, by the reaction with NBS (N-bromosuccinimide). The successive reaction of 3 with amine at room temperature afforded the alpha,beta-unsaturated gamma-methylene-gamma-lactam (2) in good yield.     

A strategy for the synthesis of metal bis(2,2':6',2' '-terpyridine)-terminated molecular dyads having controlled torsion angles at the central biphenyl linker

The synthesis of a series of binuclear complexes comprising bis(2,2':6',2' '-terpyridine)ruthenium(II) and -osmium(II) centers connected via a geometrically constrained 4,4'-biphenyl bridge is described. These compounds have been prepared by a "synthesis-at-metal" approach as well as by the conventional method of synthesizing the ligand and subsequently attaching the metal center. A computational investigation into the behavior of the biphenyl-based bridges has been used to provide lowest-energy conformations and to estimate the degree of internal fluctuation about the mean torsion angle. It is shown that the length of the constraining strap determines both the torsion angle and the internal flexibility, with longer straps twisting the biphenyl group so as to relax stereochemical interactions between the linking oxygen atoms. Longer straps can be formed from poly(ethylene glycol) residues that provide an additional binding site for small cations. Electrospray mass spectrometry carried out on solutions of these crown ether-like bridges confirmed that Li+, Na+, and K+ ions bind in the form of 1:1 complexes. This range of compounds should permit rational examination of how the torsion angle affects the rate of through-bond electron transfer, electron exchange, and charge shift.     

Conformational polymorphism and thermochemical analysis of 5,5' '-bis[(2,2,5,5-tetramethyl-1-aza-2,5-disila-1-cyclopentyl)ethyl]-2,2':5',2' ':5' ',2' '-quaterthiophene

The titled compound exists as two polymorphic solid phases (denoted form-I and form-II). Form-I obtained by as-synthesized material is a more stable phase. Form-II is a less stable phase. Spontaneous solid-solid transformation from form-II to form-I is observed in the temperature range between room temperature and the melting point of form-I (Tm = 156.5 degrees C), and its activation energy is estimated to be 96 kJ mol-1 by Arrhenius plot. The solid-solute-solid transformation (recrystallization from solution) from form-II to form-I is also observed. In contrast, form-II is obtained only by a solid-melt-solid transformation from form-I. Therefore, the system of two polymorphs is monotropic. The solid-state NMR measurement shows that form-I has the molecular conformation of complete S-syn-anti-syn in the oligothiophene backbone, whereas form-II has that of S-all-anti. With the solution NMR data, the polymorphism could not be observed. Therefore, the polymorphs originate from the different molecular packing involving the conformational change of the molecule. This unique property is attributed to the extra bulky terminal groups of the compounds. However, despite the extra bulky terminal groups, the mentioned polymorphism is not observed in the titled compound analogue which has S-all-anti conformation (like form-II).