One-pot synthesis of 5,5′-dibromo-2,2′-dipyridylacetylene and its boronic acid derivative

5,5′-Dibromo-2,2′-dipyridylacetylene was prepared from 2,5-dibromopyridine and (trimethylsilyl)acetylene via the new one-pot synthesis approach using a regioselective palladium-catalyzed coupling reaction with a 60% yield. Several protocols of lithium-halogen exchange were then attempted to synthesize 6,6′-(1,2-ethynediyl)bis[3-pyridylboronic acid] from 5,5′-dibromo-2,2′-dipyridylacetylene. The former was successfully obtained with a 54% yield by a reverse addition method using toluene and THF and it showed potential as a useful building block for cross-coupling reactions in the formation of carbon-carbon bonds.     

手性联萘基-2,2'-联吡啶及其衍生物的合成及其在不对称合成中的应用

利用Kröhnke方法,以芳基乙酮为原料一锅法简洁地合成了6-芳基-6'-溴-2,2'-联吡啶2b~2d。 通过(R)-3-(4,4,5,5-四甲基-1,3,2-二噁唑硼烷基)-2,2'-乙氧基-1,1'-联萘((R)-1)与6-溴-2,2'-联吡啶及其衍生物2a~2d的Suzuki偶联, 合成了4种手性6-[3-((R)-2,2'-二乙氧基-1,1'-联萘)基]-2,2'-联吡啶(R)-3a~3d。 将配体(R)-3a~3d应用于苯乙酮的不对称氢转移反应中,配体(R)-3a给出92%的转化率和4%的对映体过量(ee)值。     

Synthesis of vinyl-substituted polypyridyl ligands through Suzuki-Miyaura cross-coupling of potassium vinyltrifluoroborate with bromopolypyridines

Suzuki-Miyauru cross-coupling of bromopolypyridines with potassium vinyltrifluoroborate affords vinyl-substituted polypyridyl ligands in moderate to good yields. This reaction allows simple and practical syntheses of numerous vinyl-substituted polypyridines, such as 4'-vinyl-2,2':6',2'-terpyridine, 5,5'-divinyl-2,2'-bipyridine, and 4,4'-divinyl-2,2'-bipyridine. In addition, a new ruthenium complex, [Ru(5,5'-divinyl-2,2'-bipyridine)(3)](2+), was synthesized and found to undergo reductive electropolymerization smoothly.     

Heteroleptic ruthenium complexes containing uncommon 5,5'-disubstituted-2,2'-bipyridine chromophores for dye-sensitized solar cells

Four new heteroleptic ruthenium sensitizers [Ru(4,4'-carboxylic acid-2,2'-bipyridine)(L)(NCS)(2)] (L = 5,5'-bis(4-octylthiophen-2-yl)-2,2'-bipyridine (1), 5,5'-bis(N,N-diphenyl-4-aminophenyl)-2,2'-bipyridine (2), 5,5'-bis(5-(N,N-diphenyl-4-aminophenyl)-thiophen-2-yl)-2,2'-bipyridine (3) and 5,5'-bis(4-octyl-5-(N,N-diphenyl-4-aminophenyl)-thiophen-2-yl)-2,2'-bipyridine (4)) were synthesized, characterized by physicochemical and computational methods, and utilized as photosensitizers in nanocrystalline dye-sensitized solar cells (DSSCs). The λ(max) of the metal-to-ligand charge transfer (MLCT) absorption of these four ruthenium dyes (527 nm for 1, 535 nm for 2, 585 nm for 3 and 553 nm for 4) can be tuned by various structural modifications of the ancillary ligand and it was shown that increasing the conjugation length of such ligand reduces the energy as well as the molar absorption coefficient of the MLCT band. The maximum incident photon to current conversion efficiency (IPCE) of 41.4% at 550 nm, 38.6% at 480 nm, 39.4% at 470 nm and 31.1% at 480 nm for 1-, 2-, 3- and 4-sensitized solar cells were obtained. Respectable power conversion efficiencies of 3.00%, 2.51%, 2.00% and 2.03% were realized, respectively, when the sensitizers 1, 2, 3 and 4 were used in DSSCs under the standard air mass (AM) 1.5 sunlight illumination (versus 5.9% for standard N719).     

Thermotropic liquid crystals from a monosubstituted 2,2'-bipyridine

Unsymmetric functionalization of 5-bromo-2,2'-bipyridine and 5,5'-dibromo-2,2'-bipyridine with 4-n-alkoxyphenylethynyl leads to two new families of mesomorphic compounds. The smectic B, smectic A and nematic phases observed were studied by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. The structural parameters of the smectic phases were determined. The internal structure of the smectic phases, particularly the range of the in-layer ordering of the molecules, was investigated as a function of temperature.     

A selective and direct synthesis of 2-bromo-4-alkylthiophenes: Convenient and straightforward approaches for the synthesis of head-to-tail (HT) and tail-to-tail (TT) dihexyl-2,2′-bithiophenes

A straightforward method for the synthesis of 2-bromo-4-alkylthiophenes was developed, and the desired products were obtained in the highest chemical yields (>90%) reported to date. 2-Bromo-4-alkylthiophenes were synthesized by regioselective lithiating of 3-alkylthiophenes with n-BuLi and quenching with bromine at −78 °C. Moreover, a simple and efficient protocol for the synthesis of dihexyl-2,2′-bithiophenes was developed by employing 2-bromo-4-hexylthiophene instead of the commonly used monomer, 2-bromo-3-hexylthiophene. Kumada and Suzuki cross-coupling reactions were conducted to synthesize the desired products as head-to-tail (HT) and tail-to-tail (TT) regioisomers in high yields and excellent selectivity.     

Synthesis of 2,2’-Biflavanones from Flavone via Electroreduction and Photolysis

Biflavonoids, widely distributed in natural plants, had strong biological activities including spasmolysis, peripheral vasodilatation, antibradykinin activity and antispasmogenic action against prostaglandin PGE1, inhibition of cyclic GMP and cyclic AMP phosphodiesterase and inhibition of hepatoma cells. Recently, some biflavonoids were demonstrated to enhance suppersion of lymphocyte proliferation, inhibition of phospholipaseCr1, anti-inflammatory activity, anti-HIV activity, anticompleme…     

Reactions of dialkyl 4-bromo-2,2-dimethyl-3-oxohexane-1,6-dioates,-heptane-1,7-dioates with zinc and aromatic aldehydes

Zinc enolates generated from dimethyl 4-bromo-2,2-dimethyl-3-oxohexane-1,6-dioate and zinc reacted with aromatic aldehydes giving methyl 2,2-dimethyl-3-oxo-3-(5-oxo-2-aryltetrahydrofuran-3-yl)propanoates. The reaction of zinc enolates obtained from dimethyl 4-bromo-2,2-dimethyl-3-oxoheptane-1,7-dioate and zinc with aromatic aldehydes depending on the synthesis conditions led to the formation either methyl 2,2-dimethyl-3-oxo-3-(6-oxo-2-aryltetrahydropyran-3-yl)propanoates or 3-(5,5-dimethyl-4,6-dioxo-2-aryltetrahydropyran-3-yl)propanoates. The compounds synthesized formed as a single diastereomer of E-configuration.     

Oligomeric ligands incorporating multiple 5,5'-diethynyl-2,2'-bipyridine moieties bridged and end-capped by 3,4-dibutylthiophene units

In this work, we detail the synthesis and photophysical properties of a series of soluble polybipyridine ligands comprising one to five bipyridine units sandwiched between rigid carbon-carbon triple bonds substituted by 3,4-dibutylthiophene repeating units. The dual Sonogashira coupling reaction of 5,5'-dibromo-2,2'-bipyridine with TMS- and (CH3)2C(OH)-protected acetylene allows the synthesis of a dissymmetrically functionalized building block which was selectively deprotected at either the TMS or 2-hydroxyprop-2-yl site. Various combinations allow the interconnection of the terminal alkyne to 3,4-dibutyl-2,5-diiodothiophene or 3,4-dibutyl-2-iodothiophene leading to bipyridine frameworks bearing two acetylene-protected groups or one acetylenethiophene/one acetylene-protected function. It is possible therefore to construct dimeric to pentameric bipyridine ligands where the chelating subunit is bridged by a 3,4-dibutyl-2,5-diethynylthiophene spacer and end-capped by a 3,4-dibutyl-2-ethynylthiophene stopper. All cross-coupling reactions are promoted with palladium(0) tetrakistriphenylphosphine under mild conditions. Spectroscopic data for the new oligomers are discussed in terms of the extent of pi-electron conjugation. Upon increasing the number of pi-electrons from 24 to 104, there is a progressive lowering in the energy of absorption and fluorescence transitions, while the emission quantum yields remain essentially constant. The LUMO levels of these large molecules, estimated by cyclic voltammetry, lie in the range -3.06 to -3.18 eV.     

A new method of using supercritical carbon dioxide as a green solvent for synthesis and purification of 5,5‴-bis(tridecafluorohexyl)-2,2′:5′,2″:5″,2‴-quaterthiophene,which is one of n-type organic semiconducting materials

We have investigated synthesis as well as purification of 5,5?-bis(tridecafluorohexyl)-2,2′:5′,2″:5″,2?-quaterthiophene (BFH-4?T, n-type organic semiconducting material) using supercritical carbon dioxide (scCO₂) as a green solvent. BFH-4T was obtained in good selectivity and high yield by TDAE/PdCl₂-catalyzed reductive coupling reaction of 5-bromo-5′-(tridecafluorohexyl)-2,2′-bithiophene in scCO₂. We have also successfully established purification of the reaction mixture by passing scCO₂ in the reaction vessel. The product was yellow powder of BFH-4T with purity of more than 99% and Pd catalyst was not contained.     

Selective amination of polyhalopyridines catalyzed by a palladium-xantphos complex

[reaction: see text] Amination of 5-bromo-2-chloropyridine (1a) catalyzed by a palladium-Xantphos complex predominately gives 5-amino-2-chloropyridine product 3a in 96% isolated yield and excellent chemoselectivity (3a/4a = 97:3). Amination of 2,5-dibromopyridine (11) under the same conditions exclusively affords 2-amino-5-bromopyridine 4a.     

Synthesis and structural,electrochemical, and optical properties of Ru(II) complexes with azobis(2,2'-bipyridine)s

Two new ditopic ligands, 5,5"-azobis(2,2'-bipyridine) (5,5"-azo) and 5,5"-azoxybis(2,2'-bipyridine) (5,5"-azoxy), were prepared by the reduction of nitro precursors. Mononuclear and dinuclear Ru(II) complexes having one of these bridging ligands and 2,2'-bipyridine terminal ligands were also prepared, and their properties were compared with previously reported Ru(II) complexes having 4,4"-azobis(2,2'-bipyridine) (4,4"-azo). The X-ray crystal structure showed that 5,5"-azo adopts the trans conformation and a planar rodlike shape. The X-ray crystal structure of [(bpy)(2)Ru(5,5"-azo)Ru(bpy)(2)](PF(6))(4) (Ru(5,5"-azo)Ru) showed that the bridging ligand is in the trans conformation and nearly planar also in the complex and the metal-to-metal distance is 10.0 A. The azo or azoxy ligand in these complexes exhibits reduction processes at less negative potentials than the terminal bpy's due to the low-lying pi level. The electronic absorption spectra for the complexes having 5,5"-azo or 5,5"-azoxy exhibit an extended low-energy metal-to-ligand charge-transfer absorption. The ligands, 5,5"-azo and 5,5"-azoxy, and the mononuclear complex, [(bpy)(2)Ru(5,5"-azo)](2+), isomerize reversibly upon light irradiation. The low-energy MLCT state sensitizes the isomerization of the azo moiety in this complex. While [(bpy)(2)Ru(4,4"-azo)Ru(bpy)(2)](PF(6))(4) exhibits light switch properties, namely, significant electrochromism and a large luminescence enhancement, upon reduction, Ru(5,5"-azo)Ru does not show these properties. The radical anion formation upon reduction of these complexes has been confirmed by ESR spectroscopy.     

无催化剂条件下4-羟基烷基-2-炔酸乙酯与N-杂环芳基甲基-N-2,2-二氟乙基-1-胺的串联反应

开发了无催化剂条件下4-羟基烷基-2-炔酸乙酯与N-杂环芳基甲基-N-2,2-二氟乙基-1-胺的串联反应.应用该反应在甲醇中回流,以39%~83%的收率合成了一系列4-(N-(2,2-二氟乙基)(N-杂环芳基甲基)氨基)-5,5-二取代呋喃-2(5H)-酮,其结构经1H NMR,13C NMR和HR-ESI-MS表征,并进一步通过3-氯-4-(N-2,2-二氟乙基)(N-嘧啶-5-基甲基胺基)-5,5-螺(4-甲氧基环己基)呋喃-2(5H)-酮(8)的晶体衍射间接证实.测试了所合成化合物的生物活性,结果表明,在600μg·mL^-1浓度时4-(N-2,2-二氟乙基)(N-6-氯吡啶-3-基甲基胺基)-5,5-二甲基呋喃-2(5H)-酮(3a)和4-(N-2,2-二.氟乙基)(N-6-氟吡啶-3-基甲基胺基)-5,5-二甲基呋喃-2(5H)-酮(3c)对桃蚜的死亡率均为100%.     

Convenient and efficient synthesis of functionalized oligopyridine ligands bearing accessory pyrromethene-BF2 fluorophores

The synthesis of stable and highly luminescent pyridine-, bipyridine-, phenanthroline-, bipyrimidine-, and terpyridine-based ligands bearing one or two 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (bodipy) modules has demonstrated the advantages of three different protocols which have been adapted in light of the chemical stability of the alkyne-grafted starting building blocks and the chemical reactivity of the bromo-substituted starting materials. A classical method of condensation of aldehydes or acid chlorides with Kryptopyrrole has been used for direct linkage of a bodipy to the oligopyridinic platform. For the phenylethynyl-linked molecules, direct coupling between the bodipy-phenyliodo and the stable 4'-ethynyl-2,2':6',2' '-terpyridine, 6,6' '-diethynyl-2,2':6',2' '-terpyridine, 5-ethynyl-2,2'-bipyridine, 5,5'-diethynyl-2,2'-bipyridine, 6,6'-diethynyl-2,2'-bipyridine, and 5,5'-diethynyl-2,2'-bipyrimidine substrates is feasible and is promoted by Pd catalysts and sonication. This procedure provides the advantages of efficiency, versatility, and rapidity. A second set of experimental conditions is required to produce the 4-substituted pyridine, 3,8-disubstituted-1,10-phenanthroline, and 5,5' '-disubstituted-2,2':6',2' '-terpyridine derivatives. Cross coupling of a bodipy-phenylethynyl molecule with the bromo-substituted partners takes place smoothly with the pyridine but with low yields in the other cases due to the efficient formation of the homocoupled diphenylbutadiyne bodipy compounds. A third convenient protocol enabled the preparation of these target molecules in a one-pot reaction where the deprotection of the alkyne was conducted in situ by a phase-transfer process with aqueous NaOH and with Et(3)BnN(+)Cl(-) as mediator and the cross-coupling reaction realized in the benzene phase with [Pd(PPh(3))(4)] as catalyst and CuI as co-reagent. The nascent acid was quenched in the aqueous phase. This method is much more efficient when a trimethylsilyl protecting group is used instead of a propargylic alcohol. The pyridino-bodipy bases were alkylated smoothly in good yields in the presence of methyl iodide. The photophysical and electrochemical properties for these new molecules have been investigated and are discussed in terms of substitution patterns of the bipyridine and terpyridine platforms. In the pyridinium salt 18, the fluorescence from the first singlet excited state at lambda(em) = 547 nm is totally quenched at the expense of a low-lying charge-transfer emitting state located at lambda(em) = 660 nm.     

New synthetic path to 2,2'-bipyridine-5,5'-dicarbaldehyde and its use in the [3+3] cyclocondensation with trans-1,2-diaminocyclohexane

2,2'-Bipyridine-5,5'-dicarbaldehyde has been prepared in two steps by enamination of 5,5'-dimethyl-2,2'-bipyridine with Bredereck's reagent, and subsequent oxidative cleavage of the enamine groups with sodium periodate. On condensation of this dialdehyde with enantiomerically pure trans-1,2-diaminocyclohexane, the macrocyclic [3+3] hexa Schiff base has been obtained in excellent yield. Its reduction has given large macrocyclic hexaamine having three bipyridine units incorporated into the macrocycle structure.     

Facile synthesis and platinum complexes of 4',5,5'-trisubstituted-2,2':6',2'-terpyridines

The synthesis of trisubstituted 4',5,5' terpyridines is described. The strategy begins with synthesis of 2-acetyl-5-bromopyridine (3) from 2,5-dibromopyridine, substitution of the bromine in 3 using a variety of metal-catalyzed reactions and then formation of the terpyridine using the Krohnke reaction. The complexes have been prepared by reaction of [Pt(PhCN)(2)Cl(2)] with the appropriate silver salt followed by addition of the terpyridyl ligand. The crystal structure of two complexes have been determined via X-ray diffraction and the MLCT (metal-to-ligand charge-transfer) emissions determined by UV/Vis spectroscopy.     

Synthesis of novel dendritic 2,2'-bipyridine ligands and their application to Lewis acid-catalyzed diels-alder and three-component condensation reactions

A series of dendritic ligands with a 2,2'-bipyridine core was synthesized through the coupling of 4,4'-dihydroxy-2,2'-bipyridine with poly(aryl ether) dendrons. The corresponding dendritic Cu(OTf)2 catalysts were used for Diels-Alder and three-component condensation reactions. The dendritic Cu(OTf)2-catalyzed Diels-Alder reaction proceeded smoothly, and these dendritic catalysts could be recycled without deactivation by reprecipitation. Three-component condensation reactions such as Mannich-type reactions also proceeded not only in dichloromethane but also in water. Furthermore, a positive dendritic effect on chemical yields was observed in both Diels-Alder reactions and aqueous-media three-component condensation reactions.     

Synthesis of di-, tri-, and tetrasulfides through multifold carbon-sulfur cross-coupling reactions with indium tri(organothiolates) in a one-pot procedure

Pd-catalyzed multifold (2-, 3-, and 4-fold) carbon-sulfur cross-coupling reaction of indium tri(organothiolates) with polybromonated aromatic and heteroaromatic compounds was developed in a one-pot procedure. Both 2,5-dibromopyridine and 2,6-dibromopyridine reacted with indium tri(organothiolates) (0.68 equiv) in the presence of 4 mol % of Pd(OAc)(2), 4.2 mol % of Xantphos, and 1 equiv of diisopropylethylamine (DIPEA), producing disulfides in good to excellent yields. These results indicate that indium tri(organothiolates) transfer all three alkyl- or arylthio groups attached to indium metal to electrophilic coupling partners. Indium tri(organothiolates) derived from alkyl thiol having a low boiling point, such as n-propyl, isopropyl, and tert-butyl thiol, acted as good nucleophilic coupling partners. In addition, indium tri(arylthiolates) derived from aryl thiols possessing an electron-withdrawing or -donating group on the aromatic ring participated well in the Pd-catalyzed multifold carbon-sulfur cross-coupling reaction. 4,4'-Dibromo-1,1'-biphenyl, 9,10-dibromoanthracene, 2,4-dibromoanisole, 2,7-dibromo-9,9-dimethylfluorene, 3,4-dibromothiophene, 2,3-dibromothiophene, 2,2'-bithiophene, 1,3,5-tribromobenzene, and 1,2,4,5-tetrabromobenzene were converted smoothly to the corresponding di-, tri-, and tetrasulfides.     

Synthesis of 2-Bromo-2′-phenyl-5,5′-thiophene: Suzuki Reaction Versus Negishi Reaction

Abstract

2-Bromo-2′-phenyl-5,5′-thiophene was synthesized by cross- coupling reaction of phenylboric acid and 2,2′-dibromo-5,5′-bithiophene with a Suzuki reaction; we found the Suzuki reaction to give a higher yield when compared to the Negishi reaction.     

Room temperature phosphorescence from ruthenium(II) complexes bearing conjugated pyrenylethynylene subunits

We describe the synthesis, electrochemistry, and photophysical properties of several Ru(II) complexes bearing different numbers of pyrenylethynylene substituents in either the 5- or 5,5'-positions of 2,2'-bipyridine, along with the appropriate Ru(II) model complexes bearing either bromo- or ethynyltoluene functionalities. In addition, we prepared and studied the photophysical behavior of the diimine ligands 5-pyrenylethynylene-2,2'-bipyridine and 5,5'-dipyrenylethynylene-2,2'-bipyridine. Static and dynamic absorption and luminescence measurements reveal the nature of the lowest excited states in each molecule. All model Ru(II) complexes are photoluminescent at room temperature and exhibit excited-state behavior consistent with metal-to-ligand charge transfer (MLCT) characteristics. In the three Ru(II) molecules bearing multiple pyrenylethynylene substituents, there is clear evidence that the lowest excited state is triplet intraligand (3IL)-based, yielding long-lived room temperature phosphorescence in the red and near IR. This phosphorescence emanates from either 5-pyrenylethynylene-2,2'-bipyridine or 5,5'-dipyrenylethynylene-2,2'-bipyridine, depending upon the composition of the coordination compound. In the former case, the excited-state absorption difference spectra that were measured for the free ligand are easily superimposed with those obtained for the metal complexes coordinated to either one or two of these species. The latter instance is slightly complicated since coordination of the 5,5'-ligand to the Ru(II) center planarizes the diimine structure, leading to an extended conjugation on the long axis with a concomitant red shift of the singlet pi-pi absorption transitions and the observed room temperature phosphorescence. As a result, transient absorption measurements obtained using free 5,5'-dipyrenylethynylene-2,2'-bipyridine show a marked blue shift relative to its Ru(II) complex, and this extended pi-conjugation effect was confirmed by coordinating this ligand to Zn(II) at room temperature. In essence, all three pyrenylethynylene-containing Ru(II) complexes are unique in this genre of chromophores since the lowest excited state is 3IL-based at room temperature and at 77 K, and there is no compelling evidence of interacting or equilibrated excited states.