Photochemical Studies on Bicyclo[2.1.1]hexyl Derivatives: Chemical Behavior and Asymmetric Induction

The photochemical behavior of bicyclo[2.1.1]hexyl derivatives was investigated by irradiation with a 450 W medium‐pressure mercury lamp in acetonitrile solution. The irradiation of methyl bicyclo[2.1.1]hexane‐5‐carbonylbenzoate ( 1a ) led to both Norrish type II cyclization and cleavage products with a molar ratio of 1:2.2, whereas the irradiation of methyl 5‐methylbicyclo[2.1.1]hexane‐5‐carbonylbenzoate ( 1b ) afforded the only Norrish/Yang photocyclization compound as the sole product. Such results were illustrated by several geometric parameters for Norrish/Yang photoreaction as ?₁, ?₄ and β obtained from the crystal structures. Furthermore, asymmetric photochemical studies using ionic chiral auxiliary technique were also conducted in the solid state.     

Asymmetric Photochemical Reaction of 5-Methylbicyclo[1.1.1]-pentanyl Ketone

The density functional theory(DFT) calculations were performed to investigate a typical Norrish/Yang type II photoreaction of 5-methylbicyclo[1.1.1]-pentanyl ketone. The results reveal the essential correlation between structures on the one hand and energies, on the other hand, of the reactants, transition states and products based on both singlet ground(S₀) and triplet excited(T₁) potential energy surfaces. The feasible mechanism indicates that an intramolecular Norrish/Yang cyclization reaction takes place via H-abstraction to obtain the sole chiral cyclobutanol photoproduct. The located crossing point plays an important role in the cyclization process, which permits intersystem crossing(ISC) from T₁ to S₀ state. The rate-determining step may be to experience ISC between two different potential energy surfaces, requiring sufficient time for electron spin reversion, i.e., spin multiplicity alteration. These conclusions are further confirmed by the second-order M鴏ler-Plesset perturbation theory(MP2) calculations.     

二环[3.1.0]己烷酮衍生物的固相不对称光化学反应研究

由二环庚二烯为起始原料合成二环己烷酮类衍生物,以手性胺作为手性辅助剂进行固相不对称光化学反应研究,探讨了反应时间和反应温度对光化学裂解产率和对映选择性的影响,ee值最高达到75%。     

Photochemical studies on exo-bicyclo[2.1.1]hexyl and bicyclo[3.1.0]hexyl aryl ketones: two approaches for synthesis of enantiomerically enriched cyclopentene derivatives

Two approaches for the photochemical synthesis of cyclopentene derivatives through the Norrish type II cleavage reaction were described. Asymmetric studies using ionic chiral auxiliaries afforded enantiomeric excesses of up to 98% at the conversion of 85%. The results were rationalized by single X-ray crystal structures.     

High‐Performance p‐Channel Organic Semiconducting Candidates Based on Benzo[1,2‐k;4,5‐k′]difluoranthene Derivatives

Orbital promises : Frontier orbital analyses showed that the small λ⁺ value of 8,17‐di‐n‐hexylbenzo[1,2‐k;4,5‐k′]difluoranthene (DH‐BDF) is owed to the nonbonding character of the BDF framework. The calculated adiabatic ionic potential and hole mobility indicates that this compound is a p‐type air‐stable organic field‐effect transistor, which promises to be a soluble, stable and high‐performance p‐type organic semiconductor.

     

Solid‐State Asymmetric Photochemical Studies Using the Ionic Chiral Auxiliary Approach

The ionic chiral auxiliary approach to asymmetric photochemical synthesis discovered by the Scheffer group has been successfully applied to many reactions in the solid state. Enantiomeric excesses of up to 99 % were obtained using this method. After a brief introduction of absolute asymmetric synthesis, chirally modified zeolites and host–guest assemblies in asymmetric photochemistry, the bulk of this review will summarize and discuss the application of the solid state ionic chiral auxiliary technique to the Norrish type II reaction, the di‐π‐methane photorearrangement, and to a novel retro‐Claisen photorearrangement.     

Transition States of Binap–Rhodium(I)‐Catalyzed Asymmetric Hydrogenation: Theoretical Studies on the Origin of the Enantioselectivity

By using the hybrid IMOMM(B3LYP:MM3) method, we examined the binap–Rh^I‐catalyzed oxidative‐addition and insertion steps of the asymmetric hydrogenation of the enamide 2‐acetylamino‐3‐phenylacrylic acid. We report a path that is energetically more favorable for the major enantiomer than for the minor enantiomer. This path follows the “lock‐and‐key” motif and leads to the major enantiomeric product via an energetically favorable binap–dihydride–Rh^III–enamide complex. Our theoretical results are consistent with the mechanism that takes place via Rh^III dihydride formation, that is, oxidative addition of H₂ followed by enamide insertion.     

Asymmetrical Fluorene[2,3‐b]benzo[d]thiophene Derivatives: Synthesis,Solid‐State Structures,and Application in Solution‐Processable Organic Light‐Emitting Diodes

A series of novel asymmetrical fused compounds containing the backbone of fluorene[2,3‐b]benzo[d]thiophene (FBT) were effectively synthesized and fully characterized. Single‐crystal X‐ray studies demonstrated that the length of the substituent side chains greatly affects the solid‐state packing of the obtained fused compounds. DFT, photophysical, and electrochemical studies all showed that the FBTs have large band gaps, low‐lying HOMO energy levels, and therefore good stability toward oxidation. Moreover, the substituents strongly influence the fluorescence properties of the resulting FBT derivatives. The di‐n‐hexyl compound exhibits intense fluorescence in solution with the highest quantum yield of up to 91 %. Solution‐processed green phosphorescent organic light‐emitting diodes with the di‐n‐butyl derivative as the host material exhibited a maximum brightness of 14 185 cd m^?2 and a luminescence efficiency of 12 cd A^?1.     

Photochemical Transformations of Some 2‐(5‐Methylthiophen‐2‐yl)‐3‐[(naphthalen‐2‐yl)methoxy]‐4H‐chromen‐4‐ones Involving Type‐II Process

Photo‐irradiation of 2‐(5‐methylthiophen‐2‐yl)‐3‐[(naphthalen‐2‐yl)methoxy]‐4H‐chromen‐4‐ones yielded the fascinating angular tetracyclic products via cyclization involving both 2‐thienyl ring and naphthylmethoxy group via 1,4‐biradical generated in the Norrish type‐II process. The stereochemical dispositions of the products were determined by MM2 energy minimized programme and spectroscopic analysis.     

Theoretical studies on triaryamine‐based p‐type D‐D‐π‐A sensitizer

Development of triaryamine‐based nonmetallic dye sensitizers is a hot topic in the solar cell research. A series of triaryamine‐based dyes WS1 – WS7 were designed with W1 as the prototype. Density functional theory (DFT) and time‐dependent‐DFT calculations were used to investigate the effects of the attached donor D on the absorption spectra and electronic properties of the dyes. The light‐harvesting efficiency (LHE), hole injection force (ΔG_inj), dye regeneration force (ΔG_reg), and charge recombination force (ΔG_CR) for all the dyes were predicted. The insertion of D not only results in a red shift in the absorption spectra for all dyes but also achieves a broader absorption for visible light. Compared with that of the prototype, the absorption peak of the dye WS7 has a red shift of 95 nm and an oscillator strength increase of 29%. The absorption peak of WS7 is wider and stronger, and the absorption range extends to 900 nm. The LHE and ΔG_reg values of WS7 are 0.991 and ?1.49 eV, respectively. On overall evaluation, WS7 is a promising candidate of a p‐type dye sensitizer with good light absorption and dye regeneration efficiency.     

Synthesis and Solid‐state Reaction of 1‐[3′‐(Benzotriazol‐2″‐yl)‐4′ ‐hydroxybenzoyl]‐3‐methyl‐5‐pyrazolones

A new kind of UV stabilizers, 1‐(3′‐(benzotriazol‐2″‐yl)‐4′‐hydroxy‐benzoyl)‐3‐methyl‐5‐pyrazolones (1a‐d), was synthesized with the aim to bind them chemically to certain polymers. The reaction of 1d with substituted benzaldehydes 4 in the molten state at 150°C and in the solid state at room temperature produced the condensation products l‐(3′‐(5″‐chlorobenzotriazol‐2″‐yl)‐4′‐hydroxyl‐5′‐chlorobenzoyl)‐3‐methyl‐4‐arylmethylene‐5‐pyrazolones (2) and 4,4′‐arylmethylene‐bis [1‐(3′‐(5″‐chloro‐benzotriazol‐2″‐yl)‐4′‐hydroxy‐5′‐chloro‐benzoyl)‐3‐methyl‐5‐pyrazolone] s (3), respectively, as the major product. On the other hand, the reaction of 1d with 4 at 50°C in chloroform solution proceeded non‐selectively to give a mixture of 2 and 3.     

Heterocyclic Systems Containing Bridged Nitrogen Atom: Synthesis and Antibacterial Activity of 3‐(2‐Phenylquinolin‐4‐yl)/3‐(1‐p‐Chlorophenyl‐5‐methyl‐1,2,3‐triazol‐4‐yl)‐s‐triazolo[3,4‐b]‐1,3,4‐thiadiazine Derivatives

The condensation of 4‐amino‐5‐mercapto‐3‐(2‐phenylquinolin‐4‐yl)/3‐(1‐p‐chlorophenyl‐5‐methyl‐1,2,3‐triazol‐4‐yl)‐1,2,4‐triazoles 1a‐b with chloroacetaldehyde 2a‐b , ω‐bromo‐ω‐(1H‐1,2,4‐triazol‐1‐yl)acetophenone 3a‐b , chloranil 4a‐b , 2‐bromocyclohexanone 5a‐b , 2,4′‐dibromoacetophenone 6a‐b and 2‐bromo‐6′‐methoxy‐2′‐acetonaphthone 7a‐b are described. The structures of the compounds synthesized were confirmed by elemental analyses, IR, 1H NMR and mass spectra. The antibacterial activities were also evaluated.     

A Facile One‐Pot Three‐Component Synthesis of 5‐(Trifluoromethyl)‐4,7‐dihydro‐[1,2,4]‐triazolo[1,5‐a]pyrimidine Derivatives in Ionic Liquid

An efficient one‐pot synthesis of 5‐(trifluoromethyl)‐4,7‐dihydro‐7‐aryl‐[1,2,4]triazolo[1,5‐a]pyrimidine derivatives was performed via the reaction of aryl aldehyde, 3‐amino‐1,2,4‐triazole and ethyl 4,4,4‐trifluoro‐3‐oxobutanoate or 4,4,4‐trifluoro‐1‐phenylbutane‐1,3‐dione in ionic liquid. This method has the advantages of short synthetic route, operational simplicities, mild reaction conditions, high yields and eco‐friendliness.     

Studies on Properties of p—Nitrophenylazo Calix[4]arene Derivatives

The p-nitrophenylazo calix[4] arene derivatives la-ld with nonlinear optical(NLO)properties were prepared by the diazo-coupling reaction of calix[4]arene with p-nitrophenyl diazonium.The diazotization reaction of p-nltroaniline was caried out with isoamyl nitrite as a source of nitrous acid in EtONa/EtOH under refluxing conditon.X-Ray crystallographic analysis and ^1H NMR sptectra reveal that they exist as cone conformation in crystal state or in soution.HRS measurements at 1064 nm in THF indicate that p-nitrophenylazo calix[4]arenes have higher hyperpolarizability βz values than the corresponding reference compound 4-(4-nitrophenylazo)-2,6-dimethyl-phenol,without red shift of the charge transfer band.The tetrakis p-nitropheylazo calix[4]arene(2)with longer alkyl chains can form monolayer aht the air/water interface.     

Ellipsometry study of the photo‐oxidation of poly[(2‐methoxy‐5‐hexyloxy)‐ p‐phenylenevinylene]

Poly(p‐phenylenevinylene) (PPV) and its derivatives exhibit strong luminescence, being serious candidates to be used as active layers in organic light‐emitting diodes. However, the structural degradation caused by photo‐oxidation is an obstacle for commercial applications of such materials. Here, we show that spectroscopy ellipsometry is a useful technique to investigate the photo‐oxidation of poly[(2‐methoxy‐5‐hexyloxy)‐p‐phenylenevinylene] (MH‐PPV), a PPV derivative, which emits a red color light. Spectroscopy ellipsometry enables determination of the complex dielectric function—?*(E)—of MH‐PPV thin‐layer films exposed to air, in the 2.1–4.2 eV energy range, as a function of the light exposure time (t_e). By using the Lorentz model to fit the experimental ?*(E) curves, it was inferred that the interactions among polymeric chains increase with t_e. From ?*(E), it is also possible to obtain the complex refractive index, N*(E) = n + ik. At higher energies (where k ? n), n increases from 1.32 to 1.40 with the photo‐oxidation progress. The behavior of n was investigated by using the Lorenz–Lorentz equation, taking into account the contribution for n by the chromophores of MH‐PPV. The effect of photo‐oxidation, mainly due to the replacement of vinyl C?C by the ketone C?O bonds, is confirmed by Fourier transform infrared measurements, an effect that reduces the average effective polymer conjugation length. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1033–1041, 2004     

Photocurable and thermally stable polymers based on 1,4‐pentadien‐3‐one‐1‐p‐hydroxyphenyl‐5‐p‐phenyl methacrylate: Copolymerization with ethyl acrylate

1,4‐Pentadien‐3‐one‐1,5‐bis(p‐hydroxyphenyl) (PBHP) was prepared by reacting p‐hydroxybenzaldehyde and acetone in the presence of an acid catalyst. 1,4‐Pentadiene‐3‐one‐1‐p‐hydroxyphenyl‐5‐p‐phenyl methacrylate (PHPPMA) monomer was prepared by reacting PBHP dissolved in ethyl methyl ketone (EMK) with methacryloyl chloride in the presence of triethylamine. A free‐radical solution polymerization technique was used for synthesizing homo‐ and copolymers of different feed compositions of PHPPMA and ethyl acrylate (EA) in EMK as a solvent with benzoyl peroxide as a free‐radical initiator at 70 ± 1 °C. All the polymers were characterized with IR and ¹H NMR techniques. The compositions of the copolymers were determined with the ¹H NMR technique. The copolymer reactivity ratios were evolved with Kelen–Tudos (EA = 1.25 and PHPPMA = 0.09) and extended Kelen–Tudos (EA = 1.30 and PHPPMA = 0.09) methods. Q (0.48) and e (1.68) values for the new monomer (PHPPMA) were calculated with the Alfrey–Price method. UV absorption spectra for poly(PHPPMA) showed two absorption bands at 302 and 315 nm. The photocrosslinking properties of the polymer samples were examined with the solvent method. Thermal analyses of the polymers were performed with the thermogravimetric‐differential thermogravimetric technique. First, the decomposition temperatures started for poly(PHPPMA), copoly(EA‐PHPPMA) (62:38), and copoly(EA‐PHPPMA) (41:59) were at 350, 410, and 417 °C, respectively. A gel permeation chromatographic method was used for determining the polymer molecular weights (weight‐average molecular weight: 2.67 × 10⁴ and number‐average molecular weight: 1.41 × 10⁴) and polydispersity index (1.89). The solubility of the monomer and the copolymers occurred at 30 °C with solvents having different polarities. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1632–1640, 2003     

High‐quality poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] synthesized by a solid–liquid two‐phase reaction: Characterizations and electroluminescence properties

Poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV) with a molar mass of 26–47 × 10⁴ g mol^?1 and a polydispersity of 2.5–3.2 was synthesized by a liquid–solid two‐phase reaction. The liquid phase was tetrahydrofuran (THF) containing 1,4‐bis(chloromethyl)‐2‐methoxy‐5‐(2′‐ethylhexyloxy)benzene as the monomer and a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The solid phase consisted of potassium hydroxide particles with diameters smaller than 0.5 mm. The reaction was carried out at a low temperature of 0 °C and under nitrogen protection. No gelation was observed during the polymerization process, and the polymer was soluble in the usual organic solvents, such as chloroform, toluene, THF, and xylene. A polymer light‐emitting diode was fabricated with MEH‐PPV as an active luminescent layer. The device had an indium tin oxide/poly(3,4‐ethylenedioxylthiophene) (PEDOT)/MEH‐PPV/Ba/Al configuration. It showed a turn‐on voltage of 3.3 V, a luminescence intensity at 6.1 V of 550 cd/m², a luminescence efficiency of 0.43 cd/A, and a quantum efficiency of 0.57%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3049–3054, 2004     

Synthesis of Some New 6,8‐Disubstituted 7,8‐Dihydropyrimido[2,3:4,3]pyrazolo[1,5‐a]pyrimidines and 6,7,8‐Trisubstituted Pyrimido[2,3:4,3]Pyrazolo[1,5‐a]Pyrimidine Derivatives

Cyclization of 5‐cyano‐1,6‐dihydro‐4‐methyl‐2‐phenyl‐6‐thioxopyrimidine 4 with excess of 85% hydrazine hydrate afforded the 3‐amino‐4‐methyl‐6‐phenylpyrazolo[3,4‐d]pyrimidine 5 , which can react with appropriate Mannich base derivatives 13a‐c and chalcones 27a,b to yield the corresponding 6,8‐disubstituted 7,8‐dihydropyrimido[2,3:4,3]pyrazolo[1,5‐a]pyrimidines 15a‐c and 30a,b , respectively. On the other hand, the 6,7,8‐trisubstituted pyrimido[2,3:4,3]pyrazolo[1,5‐a]pyrimidine derivatives 8a‐g, 20a‐e, 36 and 38 were obtained by treatment of compound 5 with appropriate 1,3‐diketones 6a‐g , 3‐dimethylamino‐1‐(substituted)prop‐2‐enones 18a‐e , 3‐aminocrotononitrile 3 , and ethoxymethylenemalononitrile 37 under acidic condition, respectively.     

An Efficient and Green One‐pot Synthesis of 12‐Aryl‐8,9,10,12‐tetrahydrobenzo[a]xanthen‐11‐one Derivatives Promoted by Sulfamic Acid in [BMIM]BF4 Ionic Liquid

An efficient and green procedure for the synthesis of novel 12‐aryl‐8,9,10,12‐tetrahydrobenzo[a]xanthen‐11‐one derivatives has been described through one‐pot condensation of 2‐naphthol, arylaldehyde and 5,5‐dimethyl‐cyclohexane‐1,3‐dione in the presence of sulfamic acid (NH₂SO₃H) in ionic liquid 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM]BF₄). These reactions proceed with good yields under short reaction time. Furthermore, the green catalytic system can be recycled specific times with no decreases in yields and reaction rates.     

Calix[4]quinones III: The Synthesis of p‐Hydroxycalix[4]arenes by Wolff‐Kishner Reduction

The Wolff‐Kishner reduction of the half‐protected ketal calix[4]monoquinone 3 and its basic hydrolysis product 4 produced a partially reducing product 5 . When the same reduction conditions were applied to the calix[4]quinone benzoates 1 and 2 , the corresponding title compounds, p‐hydroxycalix[4]arenes ( 6 and 7 ), were afforded in one step.