N-Alkyl- and N-aryl-dithieno[3,2-b:2′,3′-d]pyrrole-containing organic dyes for efficient dye-sensitized solar cells

Two new organic sensitizers, 2-cyano-3-(6-(4-(diphenylamino)phenyl)-4-(2-ethylhexyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrol-2-yl)acrylic acid and 2-cyano-3-(6-(4-(diphenylamino)phenyl)-4-(4-(hexyloxy)phenyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrol-2-yl)acrylic acid, consisting of electron donating (triphenylamine) and electron accepting (cyanoacrylic acid) functionalities linked by two different rigidified π-spacers, N-alkyl- and N-aryl-dithieno[3,2-b:2′,3′-d]pyrrole, were designed, synthesized and applied for dye-sensitized solar cells, respectively. The materials were successfully synthesized through Knoevenagel condensation reactions. Ultraviolet–visible absorption spectra revealed that the use of either of rigidified π-spacer resulted in similar charge transfer transition, however, enhanced spectral response was observed when compared with an oligothiophene analogue. In terms of their photovoltaic performance, new dyes outperformed the reference bithiophene sensitizer when tested with nitrile-based and ionic liquid-based electrolytes.     

A new route to the versatile synthesis of thiopyrano[2,3-b:6,5-b′]diindoles via 2-(alkylthio)-indole-3-carbaldehydes

A versatile synthesis of symmetrically and unsymmetrically substituted thiopyrano[2,3-b:6,5-b′]diindoles has been developed by the condensation of 2-(alkylthio)-indole-3-carbaldehydes with indoline-2-thiones in the presence of catalytic amount of ethylenediamine diacetate (EDDA). The EDDA mediated condensation leads to a spontaneous cyclization followed by aromatization to form thiopyrano[2,3-b:6,5-b′]diindoles in quantitative yields.     

An efficient synthesis of novel spiro[[8H]indeno[2,1-b]-thiophene-8,9′-fluorene] building block for blue light-emitting materials

We have developed efficient synthetic routes to obtain a novel building block spiro[[8H]indeno[2,1-b]thiophene-8,9′-fluorene] (SITF), a monothiophene-containing spirobifluorene analogue, and constructed blue light-emitting materials, including 2′,7′-bis([1,1′-biphenyl]-4-yl)-spiro[indeno[2,1-b]thiophene-8,9′-fluorene] (BBP-SITF) and 2′,7′-bis(9,9′-spirobifluoren-2-yl)spiro[[8H]indeno[2,1-b]-thiophene-8,9′-fluorene] (BSBF-SITF). BSBF-SITF has shown to be a stable blue light-emitting material with high PL quantum efficiency (89%) and unique regioselective feature at the C2 of thiophene, which indicate that BSBF-SITF will be useful for constructing complicated optoelectronic systems.     

Different recognitions of (E)- and (Z)-1,1′-binaphthyl ketoximes using lipase-catalyzed reactions

Lipase-catalyzed hydrolysis of (E)-2-[α-(acetoxyimino)benzyl]-1,1′-binaphthyl [(±)-1a] and (Z)-2-[α-(acetoxyimino)benzyl]-1,1′-binaphthyl [(±)-1b] yielded optically active (E)-2-[α-(hydroxyimino)benzyl]-1,1′-binaphthyl [(S)-2a] and (Z)-2-[α-(hydroxyimino)benzyl]-1,1′-binaphthyl [(R)-2b], respectively, with high enantiomeric excess. Selectivity for the opposite enantiomer of the axial binaphthyl skeleton was shown by (Z)-isomer 1b against (E)-isomer 1a.     

Enantioselective synthesis of (R) and (S)-[9,9′]bi[naphtho(2,1-b)furanyl]-8,8′-diol: a furo-fused BINOL derivative

The enantioselective synthesis of [9,9′]bi[naphtho(2,1-b)furanyl]-8,8′-diol, a modified BINOL, was achieved using an inexpensive route. Both enantiomers of [9,9′]bi[naphtho(2,1-b)furanyl]-8,8′-diol were obtained with satisfactory stereoselectivities by employing two optical antipodes of phenylethylamine as chiral influence in a Cu(II)Cl₂ catalyzed oxidative coupling step.     

Synthesis and ring opening reactions of 2-glyco-1,4-dimethyl-3-nitro-7-oxabicyclo[2.2.1]hept-5-enes

The high-pressure asymmetric Diels-Alder reactions of d-galacto- (1a) and d-manno-3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitrohept-1-enitol (1b) with 2,5-dimethylfuran (2) afforded mixtures of cycloadducts, from which the (2S,3R)-3-exo-nitro (3a and 3b), (2R,3S)-3-exo-nitro (4a and 4b), and (2R,3S)-1′,2′,3′,4′,5′-penta-O-acetyl-1′-C-(1,4-dimethyl-3-endo-nitro-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl)-d-galacto-pentitol (5b) were isolated pure. Deacetylation of these compounds led to new chiral mono-, bi-, and tricyclic ethers, being their asymmetric centers arising from the chiral inductor used in the cycloaddition reaction. A ring opening mechanism through a 1-nitro-1,3-cyclohexadiene intermediate has been proposed.     

Synthesis of spiro[benzopyrazolonaphthyridine-indoline]-diones and spiro[chromenopyrazolopyridine-indoline]-diones by one-pot, three-component methods in water

The synthesis of spiro[benzo[h]pyrazolo[3,4-b][1,6]naphthyridine-7,3′-indoline]-2′,6(5H)-diones and spiro[chromeno[4,3-b]pyrazolo[4,3-e]pyridine-7,3′-indoline]-2′,6(6aH,10H)-diones via a one-pot, three-component reaction of 4-hydroxycoumarin or 4-hydroxy-1-methylquinolin-2(1H)-one, isatins and 1H-pyrazol-5-amines in water is reported.     

A practical and expeditious method for the preparation of the potential anticancer agent 5,6,11,12,17,18,23,24-octahydrocyclododeca[1,2-b:4,5-b′:7,8-b″:10,11-b?]tetraindole (CTet)

A new synthetic method to obtain the potential anticancer agent 5,6,11,12,17,18,23,24-octahydrocyclododeca[1,2-b:4,5-b′:7,8-b′′:10,11-b′′′]tetraindole (CTet), starting from 1H-indole-3-carboxaldehyde and sulfamide, is described. Although a mixture of CTet and cyclic indole trimer (CTr) is formed, higher CTet/CTr ratio (4:6) and CTet yield (15%) make our protocol more favorable than those reported in the literature. A discussion on the possible reaction mechanism is reported.     

Intramolecular amidation: synthesis of novel imidazo[2,1-b][1,3,4]thiadiazole and imidazo[2,1-b][1,3]thiazole fused diazepinones

Novel heterocyclic systems 2-alkyl/aryl-9-(2-hydroxybenzylidene)-7,9-dihydro-8H-[1,3,4]thiadiazolo[2′,3′:2,3]imidazo[4,5-d][1,2]diazepin-8-one and 9-(2-hydroxy-benzylidene)-3,3-dimethyl-3,4,7,9-tetrahydro-2H-11-thia-4b,6,7,10-tetraazaindeno[1,2-a]azulene-1,8-dione are synthesized via an intramolecular amidation reaction. An interesting ring opening and cyclization of 2-alkyl/aryl-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazole-5-carbaldehyde and 6,6-dimethyl-8-oxo-2-(2-oxo-2H-chromen-3-yl)-5,6,7,8-tetrahydroimidazo[2,1-b][1,3]benzothiazole-3-carbaldehyde are discussed.     

One-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene from o-chlorobenzaldehyde

Simple one-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) from commercially available o-chlorobenzaldehyde is reported. The procedure is also applicable to the synthesis of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT).     

A novel synthetic route for the total synthesis of (±)-uleine

In this study, a new synthetic route for the total synthesis of (±)-uleine is described. The important step in the synthesis of this alkaloid consists of an intramolecular cyclization of the D ring of the azocino[4,3-b]indole skeleton. Reduction of (N-methyl){3-β-ethyl-4-oxo-2,3,4,9-tetrahydrospiro[1H-carbazole-1,2′(1,3)dithiolane]-2-yl}-2-acetamide with borane yielded the corresponding (N-methyl){3-β-ethyl-4-hydroxy-2,3,4,9-tetrahydrospiro[1H-carbazole-1,2′(1,3)dithiolane]-2-yl}-2-acetamide, which underwent acid-catalyzed ring closure to produce azocino[4,3-b]indole core. Finally, the synthesis of (±)-uleine was completed through several steps from the azocino[4,3-b]indole core.     

Convenient preparation of chiral phase-transfer catalysts with conformationally fixed biphenyl core for catalytic asymmetric synthesis of α-alkyl- and α,α-dialkyl-α-amino acids: application to the short asymmetric synthesis of BIRT-377

Chiral phase-transfer catalysts (S)-1a, (S)-1b, and (S)-2 with conformationally fixed biphenyl cores were conveniently prepared from the known, easily available (S)-6,6′-dimethylbiphenyl-2,2′-diol 3 and (S)-4,5,6,4′,5′,6′-hexamethoxybiphenyl-2,2′-dicarboxylic acid 14, respectively, in five steps. The catalysts, (S)-1a and (S)-1b are readily applicable to asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester with excellent enantioselectivity. In particular, catalyst (S)-1b was found to exhibit the unique temperature effect on the enantioselectivity, and asymmetric alkylation of glycine derivatives at room temperature gave higher enantiomeric excess than that at 0 °C. In addition, the catalyst (S)-2 exhibited the high catalytic performance (0.01-1 mol %) in the asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester and N-(p-chlorophenylmethylene)alanine tert-butyl ester compared to the existing chiral phase-transfer catalysts, thereby allowing to realize a general and useful procedure for highly practical enantioselective synthesis of structurally diverse natural and unnatural α-alkyl-α-amino acids as well as α,α-dialkyl-α-amino acids. This approach is successfully applied to the short asymmetric synthesis of cell adhesion BIRT-377.     

Synthesis of 2,9-dialkylated phenanthro[1,2-b:8,7-b′]dithiophenes via cross-coupling reactions and sequential Lewis acid-catalyzed regioselective cycloaromatization of epoxide

Phenanthro[1,2-b:8,7-b′]dithiophene (PDT) was prepared via Suzuki–Miyaura or Negishi cross-coupling of a 2-thienylboron or -zinc compound with 1,4-dibromobenzene, followed by Lewis acid-catalyzed regioselective cycloaromatization of the epoxide. A series of 2,9-dialkylated phenanthro[1,2-b:8,7-b′]dithiophene (PDT) derivatives could also be synthesized in good yields by Suzuki–Miyaura coupling of the brominated PDT with alkylboranes by introducing linear alkyl substituents.     

From N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine to propeller-shaped N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)-amine: syntheses and structures

Three unique propeller-shaped helicenyl amines compounds: N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine (1), N-phenyl-N,N-di(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (2), and N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (3) were efficiently synthesized by Wittig reaction and oxidative photocyclization. The crystal structures of 1, 2 and molecular configuration optimization (DFT-B3LYP/6-31+G(d)) of 3 reveal that the steric hindrance from the moiety of trithia[5]helicene effectively forces the nitrogen atom and the three bonded carbon atoms to coplanar and the interplanar angles of the facing terminal thiophene ring and benzene ring becoming larger when the helical arm increased from 1 to 3. Electrochemical properties and UV–vis absorption behaviors of 1, 2, 3 were primarily determined by the moiety of trithia[5]helicene.     

Functionalization of ‘kite’ shaped styryl end-capped benzodithiophene with ketone groups: synthesis, characterization and properties

We report the synthesis of a new bridged end-capped distyryldithiophene with ketone groups on the bridge: E,E-2,7′-bis((2-phenyl)-ethenyl)-benzo[2,1-b:3,4-b′]dithiophene-4,5-dione 1. Optical and electrochemical properties of 1 in solution were investigated by UV-vis absorption and cyclic voltammetry and compared to the unsubstituted parent molecule (KDS2T). Morphology of 1-based thin films was investigated by scanning electron microscopy (SEM) and the crystalline structure characterization by X-ray diffraction (XRD). Thin films were implemented as active layers into organic thin-film transistors (OTFT) in top contact configuration to evaluate the charge transport properties.     

Effect of spacer insertion in a commonly used dithienosilole/benzothiadiazole-based low band gap copolymer for polymer solar cells

Dithienosilole-benzothiadiazole based low bandgap copolymers remain promising material for organic photovoltaics. A new copolymer, poly[(4,4′-dioctyldithieno[3,2-b:2′,3′-d]silole-2,6-diyl)-alt-{4,7-bis[2-(3-hexyl)thienyl]-2,1,3-benzothiadiazole-5,5′-diyl}] (PDTSDTBT) was designed by introducing a thiophene spacer bearing a hexyl chain at β-position in the main backbone and compared to its analog poly[(4,4′-dioctyldithieno[3,2-b:2′,3′-d]silole-2,6-diyl)-alt-(2,1,3-benzothiadiazole-4,7-diyl)] (PDTSBT). In PDTSDTBT, linear alkyl chains on silicon were chosen due to facile and cheap access and the inserted 3-hexylthiophene units were chosen to increase solubility and molar mass, a weak point with PDTSBT. The two parameters are important to optimize photovoltaic performances. To compare characteristics, PDTSDTBT of molar masses greater than, and equal to a sample of PDTSBT, were prepared. Pd-catalyzed Stille cross-coupling reactions in a micro-wave reactor to promote an efficient copolymerisations. A strong absorption ranging from 370 nm to 800 nm and a good thermal stability were observed. PDTSDTBT showed better solubility and higher degree of crystallinity. Facile synthesis of high molar masses meant that higher efficiencies, around 40% greater, could be obtained with PDTSDTBT. The polymer was demonstrated to be susceptible to improvement through the use of device-additives. For example, under initial optimisations using PDTSDTBT:PC₆₀BM blend at a ratio of 1:1 delivered a power conversion efficiency of 2.13% with J_SC = 7.73 (mA/cm²), under AM 1.5 (100 mW/cm²) illumination.     

One-pot synthesis of novel spiro 2,3,7,8-tetrahydro-benzo[1,2-b:5,4-b′]dipyran-4,6-dione and 2,3,8,9-tetrahydro-benzo[1,2-b:4,3-b′]dipyran-4,10-dione derivatives

An efficient synthesis of novel spiro 2,3,7,8-tetrahydro-benzo[1,2-b:5,4-b′]dipyran-4,6-dione and 2,3,8,9-tetrahydro-benzo[1,2-b:4,3-b′]dipyran-4,10-dione derivatives in high yields under microwave irradiation is described. The reaction was also studied under conventional heating conditions.     

Facile synthesis of regio-isomeric naphthofurans and benzodifurans

Naphtho[1,2-b]furans 1a-f, naphtho[2,1-b]furans 2a-f, benzo[1,2-b:5,4-b′]difurans 3a-b, benzo[1,2-b:4,5-b′]difurans 4a-b, and benzo[1,2-b:4,3-b′]difurans 5a-b were synthesized by base-catalyzed cyclization reaction of the corresponding o-alkoxybenzoylarene derivatives. The o-alkoxybenzoylarenes were obtained from the etherification reaction of the o-hydroxybenzoylarenes, which were prepared either by the reaction of methoxyarenes with benzoyl chloride in the presence of aluminum chloride or by photo-Fries rearrangement of aryl benzoates.     

Fluorescent cyclopentadithiophene derivatives having phenyl-substituted silyl moieties

4,4-Dimethylcyclopenta[2,1-b:3,4-b′]dithiophene derivatives bearing trimethyl-, dimethylphenyl-, diphenylmethyl-, or triphenyl-silyl moieties were synthesized. The introduction of the silyl moieties onto cyclopenta[2,1-b:3,4-b′]dithiophene induced fluorescent emission as well as the bathochromic shift of wavelength at the maximum absorption and fluorescence. It was found that the larger number of phenyl group on silyl moiety resulted in the higher fluorescence quantum yield.     

SnCl4-mediated oxidative biaryl coupling reaction of 1-naphthol and subsequent ring closure of 2,2′-binaphthol to the dinaphthofuran framework

A simple method for the direct synthesis of 2,2′-binaphthols 2 and dinaphtho[1,2-b;2′,1′-d]furans 3 under mild conditions was developed, utilizing a biaryl coupling reaction via electron donor-acceptor complexes of 1-naphthols with SnCl₄. Heating of the complex in a sealed tube for (18-24 h) afforded the corresponding o-o coupled product 2 in excellent yield. Prolonged reaction (56-65 h) under the same conditions afforded 3 in high yield in one step. We also found that in the case of α-naphthol without substituents other than a hydroxyl group at the C-1 position, regioselective o-o coupling reaction proceeded. The products 2a, 2b and 2g should be useful as synthetic intermediates for naturally occurring 3,3′-bijuglone, 3,3′-biplumbagin and elliptinone.