A new mesogenic fluorene derivative: 2,7-bis(4-pentylphenyl)-9,9-diethyl-9H-fluorene

The title compound, 2,7-bis(4-pentylphenyl)-9,9-diethyl-9H-fluorene, is a new mesogenic compound containing the fluorene moiety. It exhibits a monotropic nematic liquid crystalline behaviour, with isotropisation temperature of 53°C. The compound is also polymorphic in the solid state, with one crystal phase melting at 103°C and another one melting at 71°C. The crystal and molecular structure of the high melting solid phase have been determined from single crystal X-ray diffraction analysis. Crystals are monoclinic, with cell dimensions a = 16.649(6) Å, b = 8.305(3) Å, c = 24.598(7) Å, β = 111.60(2)?, space group P2₁/c and four molecules in the unit cell. Refinement leads to R = 0.0558. The two terminal alkyl chains and one phenyl ring are disordered over two split positions. The imbricated molecular packing observed in the solid state seems to resemble that of the nematic phase that is formed upon cooling the melt.     

Synthesis and structure of 9,10-bis(2,4,6-triisopropylphenyl)-9,10-dihydro-9,10-disilaanthracene

We prepared a 9,10-dihydro-9,10-disilaanthracene (DSA) derivative 4 bearing a bulky aryl substituent, a 2,4,6-triisopropylphenyl (Tip) group, on the silicon atoms via a Wurtz-type coupling reaction between two molecules of (2-chlorophenyl)(2,4,6-triisopropylphenyl)silane (3) in a head-to-tail fashion. The structural determination of cis-4 and trans-4 was examined using ¹H NMR spectroscopy and theoretical calculations. In addition, the molecular structure of cis-4 was unambiguously determined by X-ray crystallography. The tricyclic DSA skeleton of cis-4 adopts a folded structure with a boat-like central ring in which the rotation about the Si-Tip bond is restricted. In contrast, theoretical calculations suggest that the tricyclic DSA skeleton of trans-4 has an almost planar structure.     

2,7-Disubstituted proton sponges as borderline systems for investigating barrier-free intramolecular hydrogen bonds. Protonated 2,7-bis(trimethylsilyl)- and 2,7-di(hydroxymethyl)-1,8-bis(dimethylamino)naphthalenes

Protonated 2,7-bis(trimethylsilyl)- and 2,7-di(hydroxymethyl)-1,8-bis(dimethylamino)naphthalenes have been prepared and studied by a combination of X-ray crystallography at room and low temperatures, IR and NMR spectroscopic techniques in conjunction with quantum-chemical calculations. It was demonstrated that the intramolecular [NHN]⁺ hydrogen bond in the 2,7-bis(trimethylsilyl) system, being sterically compressed, is the shortest among all known aromatic diamine systems. Nevertheless, as it is evidenced by the primary ¹H/²H isotope effect, IR spectra and MP2 calculations, a double minimum potential for the proton motion still exists with a very low barrier estimated to be about 0.7 kcal/mol. An influence of a counter-anion on the NH proton involving the spatially hindered H-bond is also considered.     

Polymer-supported (2,6-dichloro- 4-alkoxyphenyl)(2,4-dichlorophenyl)methanol: a new linker for solid-phase organic synthesis

An acid and base stable hydroxytetrachlorodiphenylmethyl (HTPM) linker is developed for polymer-supported organic synthesis. The linkers reported here are utilized for loading carboxylic acids, amines, alcohols, and phenols, and are stable to Br?nsted and Lewis acids, Br?nsted bases, and a wide variety of nucleophiles. However, the HTPM linkers can conveniently be cleaved by the solvolytic displacement reactions with 20% TFA. [structure: see text]     

Microwave-assisted ketone-ketone rearrangement: an improved synthesis of 3-(4-alkoxyphenyl)-3- methylbutan-2-ones

[reaction: see text] A novel procedure for the preparation of 3-(4-alkoxyphenyl)-3-methylbutan-2-one in excellent yield is described via polymer-supported AlCl3-catalyzed rearrangement of 1-(4-ethoxyphenyl)-2,2-dimehtylpropan-1-one, followed by O-alkylation under microwave irradiation condition.     

6,13-dibromopentacene [2,3:9,10]-bis(dicarboximide): a versatile building block for stable pentacene derivatives

6,13-Dibromopentacene [2,3:9,10]-bis(dicarboximide) (1) was synthesized for the first time by using in situ generated benzo[1,2-c:4,5-c']difuran as a key intermediate. Compound 1 exhibits good photostability in comparison to other pentacene derivatives and it can be further functionalized by Pd-catalyzed coupling reactions to give a series of soluble and stable functional pentacenes.     

2-phenyl-4-bis(methylthio)methyleneoxazol-5-one: versatile template for diversity oriented synthesis of heterocycles

4-Bis(methylthio)methylene-2-phenyloxazol-5-one (1) has been shown to be a versatile template for the synthesis of novel heterocyclic scaffolds. The key protocol involves nucleophilic ring opening of 1 with various primary aliphatic, aromatic amines and diamines to give open-chain amide adducts which are transformed into 4-bis(methylthio)methylene-2-phenyl-1-alkyl/arylimidazol-5-(4H)-ones (5) in good yields in the presence of anhydrous NaOAc/AcOH. Similarly, the amide adducts 4h-i from 3,4-dimethoxyphenylethylamine and tryptamine undergo interesting rearrangement in the presence of POCl(3) to furnish 1-(2-phenyl-5-methylthio-4-thiazolyl)dihydroisoquinoline and β-carboline derivatives 8-9 in good yields. The amide adduct 14 from o-phenylenediamine on exposure to refluxing acetic acid or in the presence of Ag(2)CO(3) affords substituted 3H-1,5-benzodiazepinone, 2-(5-methylthio-2-phenyl-4-oxazolyl)-1H-benzimidazole and trisubstituted oxazole (15-17), whereas the bis-adduct from ethylenediamine yields ethylene bridge tethered bis-imidazole 23 and bis-oxazole 24 under similar reaction conditions. Probable mechanisms for the formation of various products have been suggested.     

Molecular structure of 9,10-bis[bis(4-tert-butylphenyl)methylene)-9,10-dihydroanthracene: A butterfly-shaped Thiele's hydrocarbon derivative

The molecular structure of 9,10-bis[bis(4-tert-butylphenyl)methylene)-9,10-dihydroanthracene, an anthraquinodimethane derivative having four aryl groups on exocyclic methylene positions, was experimentally and theoretically characterized. Single-crystal diffraction study revealed that the title molecule takes a butterfly shape, i.e., two exocyclic carbons rise from the molecular plane, defined by four carbons of central quinoidal ring, by 1.257(3) Å (average). The dihedral angle of the butterfly wing, i.e., the angle between the two annulated benzenes is 137.71(5)°. Characteristic bond alternation was observed for the central quinoidal moiety and the exocyclic double bond. Theoretical study indicated that this butterfly shape is the stable structure. The two optimized structures nearly reproduced the experimentally observed molecular structures, bond distances, and angles.     

On the methylation of 5-(4-alkoxyphenyl)-15-(4-pyridyl)porphyrins

Mixed condensation of 3,3′-diethyl-4,4′-dimethyl-2,2′-dipyrrolylmethane 1 with 4-formylpyridine 2 and 4-alkoxybenzaldehyde 3 in acid medium and subsequent oxidation of the reaction mixture with DDQ gives, among other compounds, title compound 5 . An efficient methylation procedure of the pyridyl group in 5-(4-alkyoxyphenyl)-15-(4-pyridyl)porphyrins is described. Mixed condensation of 1 with N-methyl-4-formylpyridinium salt 9 and 3 yields among other compounds 5-(4-N-methylpyridiniumiodide)porphyrin 10 .     

New synthesis of (Z,E)-2,7-bis(4-cyanobenzylidene)cycloheptan-1-one under stereospecific constraints induced by host-guest interactions

A selective, efficient, and fast access to (Z,E)-2,7-bis(4-cyanobenzylidene)cycloheptan-1-one (BCBCH), precursor of the synthetic antagonist of tissue-plasminogen activator (t-PA), is reported using a solid/solid aldolisation-crotonisation reaction on a supramolecular complex under microwave irradiation. The underlying mechanism is investigated from the crystal structure of the intermediate host-guest complex formed between permethylated gamma-cyclodextrin and (Z)-2-(4-cyanobenzylidene)cycloheptan-1-one.     

A new series of 2,5-bis(4-methylphenyl)-1,3,4-oxadiazole derivatives: their synthesis and fluorescence properties for anion sensors

A new series of 2,5-bis(4-methylphenyl)-1,3,4-oxadiazole derivatives containing various substituted groups on the ortho-position to oxadiazole ring was synthesized and their fluorescent sensor properties were investigated. The fluorescent sensor molecules showed UV absorption shift as well as fluorescence emission shift upon exposure to fluoride anion in DMF solution, which was considerably dependent on the substituent attached on the phenyl group. The new sensory compound, 1d can be used as a fluoride anion sensor in terms of naked-eye detection and fluorescent sensing with high selectivity.     

A versatile method for cyclic polymers from conjugated and unconjugated vinyl monomers

A versatile method was introduced to prepare cyclic polymers from both conjugated and unconjugated vinyl monomers. It was developed on the combination of the RAFT polymerization and the self‐accelerating double strain‐promoted azide‐alkyne click (DSPAAC) reaction. In this approach, a switchable chain transfer agent 1 was designed to have hydroxyl terminals and a functional pyridinyl group. The protonation and deprotonation of pyridinyl group endowed the chain transfer agent 1 with a switchable control capability to RAFT polymerization of both conjugated and unconjugated vinyl monomers. Based on this, RAFT polymerization and the following hydroxyl end group modification were used to prepare various azide‐terminated linear polymers including polystyrene, poly(N‐vinylcarbazole), and polystyrene‐block‐poly(N‐vinylcarbazole). Using sym‐dibenzo‐1,5‐cyclooctadiene‐3,7‐diyne (DBA) as small linkers, the corresponding cyclic polymers were then prepared via the DSPAAC reaction between DBA and azide terminals of the linear precursors. Due to the self‐accelerating property of DSPAAC reaction, this bimolecular ring‐closing reaction could efficiently produce the pure cyclic polymers using excess molar amounts of DBA to linear polymer precursors. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1811–1820     

Bis(2-thienyl)silanes: new, versatile precursors to arylsilanediols

Silanediols have been shown to be effective bioisosteres for the hydrated carbonyl group. Current methods for the formation of silanediols place a number of constraints on how and where this functionality may be used. A range of arylsilanes that would allow both the formation of arylsilanediols and that are also compatible with multi-step synthetic routes, have been investigated as possible precursors to silanediols. Through this study bis(2-furyl)silanes and, in particular, bis(2-thienyl)silanes have been identified as practical precursors to arylsilanediols.     

Synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)nfluoren-9-one and 9-(p-methoxyphenyl)-9-methyl derivatives: optical properties

2,7-Substituted 9-fluorenones and 9,9-disubstituted fluorene have been synthesized and their fluorescence properties analyzed. The synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluoren-9-one (or the 9-(p-methoxyphenyl)-9-methyl) structures was carried out by the heterocoupling reaction between the 2,7-di(halo)fluoren-9-one (or 2,7-dibromo-9-(p-methoxyphenyl)-9-methylfluorene) and p-trimethylsilylethynyl(phenylethynyl)_n (n=1,2), catalyzed by the dichloro bis(triphenylphosphine)palladium and cuprous iodide system, in a divergent synthesis.The π-extended conjugated compounds exhibit fluorescence radiation emission (blue light-emitting), with important quantum yield for the 9-(p-methoxyphenyl)-9-methyl-2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluorenes which increases with the conjugation.     

A new versatile synthesis of 4-substituted diaminopyridine derivatives

A new convenient method for the synthesis of substituted 2,6-diacetamido pyridines has been developed. It starts from 4-hydroxypyridine and comprises the introduction of the amino groups by the Chichibabin reaction. After several protection and deprotection steps 2,6-diacetamido-4-hydroxy pyridine is obtained, which is regarded as a key compound for the synthesis of various substituted 2,6-diacetamido pyridines. It is shown that the free hydroxy group is susceptible for nucleophilic substitution. This provides an easy access to the introduction of different functional groups at 4-position of 2,6-diacetamido pyridine. The advantages over other procedures described in the literature are discussed.     

(R)-2,4-Dihydroxybutyramide seco-pseudonucleosides: new versatile homochiral synthons for synthesis of modified oligonucleotides

[reaction: see text] Two series of seco-pseudonucleoside synthons were synthesized from (R)-(+)-alpha-hydroxy-gamma-butyrolactone and (R)-(-)-pantolactone by aminolysis, side-chain protection, dimethoxytritylation, and phosphitylation or solid-phase attachment. The phosphoramidites and solid supports were used in automated DNA synthesis to prepare oligonucleotides modified with one or more 2,4-dihydroxybutyramide units bearing side-chain reporter groups. These new oligonucleotide modification reagents allow the introduction of a label into any desired position within an oligonucleotide chain during solid-phase assembly.     

Synthesis of acrylate and norbornene polymers with pendant 2,7-bis(diarylamino)fluorene hole-transport groups

New hole-transport monomers have been synthesized in which a 2,7-(diarylamino)fluorene hole-transport functionality is linked through the 9-position of the fluorene bridge to a polymerizable acrylate or norbornene group; these monomers have been polymerized under free-radical and ring-opening metathesis polymerization (ROMP) conditions, respectively. The norbornene monomer has also been copolymerized with a cinnamate-functionalized norbornene; this copolymer can be rendered insoluble through photo-crosslinking of the cinnamate groups under UV irradiation, thus permitting the use of the polymer in organic electronic devices based upon multiple polymer layers. The norbornene monomer has also been copolymerized with dicyclopentadiene to afford insoluble crosslinked films. Time-of-flight studies indicate that the norbornene polymer has a higher hole mobility than the analogous acrylate material, consistent with the predictions of the disorder formalism.