Synthesis of through‐space conjugated polymers containing [2.2]paracyclophane and thieno[3,4‐b]pyrazine in the main chain

We synthesized through‐space conjugated polymers with [2.2]paracyclophane and thieno[3,4‐b]pyrazine units in the main chain by the Sonogashira–Hagihara coupling reaction. The obtained polymers were soluble in common organic solvents, and homogeneous thin films were readily obtained from the polymer solutions by spin‐coating techniques. The polymers exhibited the extension of the conjugation length via the through‐space interaction. The polymers showed orangish‐red emission with peak maxima of around 610 nm in diluted solutions and their thin films, which were derived from the thieno[3,4‐b]pyrazine moieties. The optical and electrochemical behaviors of the polymers containing pseudo‐para‐ and pseudo‐ortho‐linked [2.2]paracyclophane were identical. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Syntheses of New Unsymmetrical 2,5‐Disubstituted‐1,3,4‐oxadiazoles and 1,2,4‐Triazolo[3,4‐b]‐1,3,4‐thiadiazoles Bearing Thieno[2,3‐c]pyrazolo Moiety

New series of (thieno[2,3‐c]pyrazolo‐5‐yl)‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazoles 10a , 10b , 10c and (thieno[2,3‐c]pyrazol‐5‐yl)‐1,3,4‐oxadiazol‐3(2H)‐yl)ethanones 6a , 6b , 6c has been synthesized from thieno[2,3‐c]pyrazole‐5‐carbohydrazide 3 by multistep reaction sequence. (5‐Aryl‐1,3,4‐oxadiazol‐2‐yl)‐1H‐thieno[2,3‐c]pyrazoles 4a , 4b , 4c were also synthesized from thieno[2,3‐c]pyrazole‐5‐carbohydrazide 3 by cyclization with various aromatic carboxylic acids. The hydrazide 3 was obtained by reaction of thieno[2,3‐c]pyrazole‐5‐carboxylate 2 with hydrazine hydrate in good yield, and compound 2 was obtained by the reaction of 5‐chloro‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde 1 and 2‐ethyl thioglycolate in presence of sodium alcoholate in good yield.     

Pyridine‐2(1H)‐thiones: Versatile Precursors for Novel Pyrazolo[3,4‐b]pyridine,Thieno[2,3‐b]pyridines,and Their Fused Azines

Pyridine‐2(1H)‐thiones were prepared and reacted with several active halogenated reagents to afford novel thieno[2,3‐b]pyridines in excellent yields. Thieno[2,3‐b]pyridine‐2‐carbohydrazide derivative was prepared by the reaction of either ethyl 2‐((3‐cyanopyridin‐2‐yl)thio)acetate derivative or thieno[2,3‐b]pyridine‐2‐carboxylate derivative with hydrazine hydrate. On the other hand, the reaction of either pyridine‐2(1H)‐thione or ethyl 2‐((pyridin‐2‐yl)thio)acetate derivative with hydrazine hydrate afforded the corresponding 1H‐pyrazolo[3,4‐b]pyridine derivative. Thieno[2,3‐b]pyridine derivatives reacted with several reagents to afford the corresponding pyrimidine‐4(3H)‐ones and [1,2,3]triazin‐4‐(3H)‐one. Moreover, 2‐carbohydrazide derivative reacted with β‐dicarbonyl reagents to give 2‐((3‐methyl‐1H‐pyrazol‐1‐yl)carbonyl)thienopyridines. The structure of the target molecules is elucidated using elemental analyses and spectral data.     

Selective Synthesis of 1,2‐Diarylpyrrolo[3,4‐b]pyridine‐5,7‐diones via Cyclization Reaction of β‐Enamino Imides with Cinnamaldehydes

The novel 1,2‐diaryl substituted pyrrolo[3,4‐b]pyridine‐5,7‐diones were selectively synthesized in high yields by the base catalyzed cyclization reaction of 3‐arylamino‐1‐methyl‐1H‐pyrrole‐2,5‐diones with cinnamaldehyde and its derivatives in acetonitrile at room temperature. However, when piperidinium trifluoroacetate was employed as catalyst, the reaction afforded a mixture of 1,2‐diaryl and 1,4‐diaryl substituted pyrrolo[3,4‐b]pyridine‐5,7‐diones in comparable yields.     

Reactions of hydrazonoyl halides 43 : Synthesis of some new 2,3‐dihydro‐1,3,4‐thiadiazoles,pyrazoles, pyrazolo[3,4‐d]‐pyridazines,thieno[2,3‐b]pyridines,pyrimidino[4′,5′:4,5]thieno[2,3‐b]‐pyridines and pyrrolo[3,4‐d]pyrazoles

2,3‐Dihydro‐1,3,4‐thiadiazoles, pyrazoles, pyrazolo[3,4‐d]pyridazines, thieno[2,3‐b]pyridines, pyrim‐idino[4′,5′:4,5]thieno[2,3‐b]pyridines and pyrrolo[3,4‐d]pyrazoles were obtained in a good yields by treatment of hydrazonoyl halides with each of alkyl carbodithioates, 3‐(dimethylamino)‐1‐naphtho[1,2‐d]furan‐2‐ylprop‐2‐en‐1‐one and N‐arylmalemides.     

Synthesis of some new bipyridines,thieno[2,3‐b]pyridines,and pyrazolo[3,4‐b]pyridines

Cyclocondensation of cyanoacetamide and cyanothioacetamide with sodium salt of 3‐hydroxy‐1‐(pyridin‐3‐yl)prop‐2‐en‐1‐one gave 6‐oxo‐[2,3′]bipyridine 5a and 6‐thioxo‐[2,3′]bipyridine 5b derivatives, respectively. Compound 5b upon treatment with different methylenes 8 gave thieno[2,3‐b]pyridines 10 . Treatment of 5b with iodomethane gave bipyridine derivative 7 , which cyclocondensed with hydrazines 11 to give pyrazolo[3,4‐b]pyridines 13 . J. Heterocyclic Chem., (2012).     

One‐Pot Synthesis of 1,4‐Oxathiino[2,3‐b]quinoxalines or ‐pyrazines from 2,3‐Dichloroquinoxaline or ‐pyrazine and 1‐Aryl‐2‐bromoalkan‐1‐ones

An efficient one‐pot synthesis of novel heterocyclic derivatives, 2‐aryl‐1,4‐oxathiino[2,3‐b]quinoxalines or ‐pyrazines 5 , via the reaction of 2,3‐dichloroquinoxaline or ‐pyrazine with Na₂S?9 H₂O, and subsequent treatment of the resulting 2‐chloro‐3‐sodiosulfanylquinoxaline or ‐pyrazine 2 with 1‐aryl‐2‐bromo‐1‐alkanones and then NaH under mild conditions is described.     

Three‐Step Synthesis of 3‐Aryl‐2‐sulfanylthieno[2,3‐b]‐, ‐[2,3‐c]‐, or ‐[3,2‐c]pyridines from the Corresponding Aryl(halopyridinyl)methanones

A convenient three‐step procedure for the synthesis of three types of 3‐aryl‐2‐sulfanylthienopyridines 4, 8 , and 12 has been developed. The first step of the synthesis of thieno[2,3‐b]pyridine derivatives 4 is the replacement of the halo with a (sulfanylmethyl)sulfanyl group in aryl(2‐halopyridin‐3‐yl)methanones 1 by successive treatment with Na₂S?9 H₂O and chloromethyl sulfides to give aryl{2‐[(sulfanylmethyl)sulfanyl]pyridin‐3‐yl}methanones 2 . In the second step, these were treated with LDA (LiNⁱPr₂) to give 3‐aryl‐2,3‐dihydro‐2‐sulfanylthieno[2,3‐b]pyridin‐3‐ols 3 , which were dehydrated in the last step with SOCl₂ in the presence of pyridine to give the desired products. Similarly, thieno[2,3‐c]pyridine and thieno[3,2‐c]pyridine derivatives, 8 and 12 , respectively, can be prepared from aryl(3‐chloropyridin‐4‐yl)methanones 5 and aryl(4‐chloropyridin‐3‐yl)methanones 9 , respectively.     

Synthesis and photovoltaic performance of donor–acceptor polymers containing benzo[1,2‐b:4,5‐b′]dithiophene with thienyl substituents

Three alternating donor–acceptor copolymers have been synthesized by Stille coupling polymerization of 2,6‐(trimethyltin)?4,8‐bis(5‐dodecylthiophene‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene with 1,3‐dibromo‐5‐hexylthieno[3,4‐c]pyrrole‐4,6‐dione, 4,7‐dibromo‐1,3‐benzothiadiazole, and 5,7‐dibromo‐2,3‐didodecylthieno[3,4‐b]pyrazine, respectively. The synthesized polymers were tested in bulk heterojunction solar cells as blends with the acceptor [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM). The thienopyrroledione copolymer displayed a power conversion efficiency of 3.00% which was increased to 3.86% by application of the additive 1,8‐diiodooctane (DIO). Tapping mode atomic force microscopy analysis indicated that there was an increase in the phase separation between polymer and PCBM, leading to an improvement in the performance upon the addition of DIO. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2622–2630     

Stacking patterns of thieno[3,2‐b]thiophenes functionalized by sequential palladium‐catalyzed Suzuki and Heck cross‐coupling reactions

The crystal structures of three 5‐alkenyl‐2‐arylthieno[3,2‐b]thiophenes, namely 3,6‐dibromo‐5‐(4‐tert‐butylstyryl)‐2‐(naphthalen‐1‐yl)thieno[3,2‐b]thiophene, C₂₈H₂₂Br₂S₂, (I), 3,6‐dibromo‐5‐(4‐methylstyryl)‐2‐(naphthalen‐1‐yl)thieno[3,2‐b]thiophene, C₂₅H₁₆Br₂S₂, (II), and 3,6‐dibromo‐2‐(4‐tert‐butylphenyl)‐5‐(4‐methylstyryl)thieno[3,2‐b]thiophene, C₂₅H₂₂Br₂S₂, (III), have been determined in order to evaluate the geometry of the molecules. The π‐conjugated system containing the thieno[3,2‐b]thiophene skeleton, the ethylene bridge and the phenyl rings is almost planar. The aromatic ring directly attached to the thieno[3,2‐b]thiophene moiety is not coplanar with the thieno[3,2‐b]thiophene moiety itself due to steric hindrance of the bromo substituent. The crystal packings are characterized by π–π stacking [only for (II)] and C—Br...π interactions. The long axes of the molecules in (I) are oriented in two directions; for the two other structures the long axis is oriented in one direction only.     

A New Four‐Component Reaction for the Synthesis of Spiro[4H‐indeno[1,2‐b]pyridine‐4,3′‐[3H]indoles]

A new four‐component synthesis of spiro[4H‐indeno[1,2‐b]pyridine‐4,3′‐[3H]indoles] and spiro[acenaphthylene‐1(2H),4′‐[4H‐indeno[1,2‐b]pyridines] by the reaction of indane‐1,3‐dione, 1,3‐dicarbonyl compounds, isatins (=1H‐indole‐2,3‐diones) or acenaphthylene‐1,2‐dione, and AcONH₄ in refluxing toluene in the presence of a catalytic amount of pyridine is reported.     

Synthesis of oxazolo[3,2‐b]hetero[1,2,4]thiadiazine S,S‐dioxides

Six bromomethyl derivatives of the new 2,3‐dihydrooxazolo[3,2‐b]thieno[3,4‐e][1,2,4]thiadiazine 5,5‐dioxides, 2,3‐dihydrooxazolo[3,2‐b]thieno[2,3‐e][1,2,4]thiadiazine 5,5‐dioxides and 6,7‐dihydrooxazolo‐[3,2‐b]pyrazolo[4,3‐e][1,2,4]thiadiazine 9,9‐dioxides heterocyclic ring systems were synthesized. These compounds are good intermediates for the preparation and development of promising antiviral and psy‐chotropic drugs. The structures of the products are supported by different nmr spectroscopic methods and mass spectrometry.     

Using Calcium Carbide as an Acetylene Source for Cascade Synthesis of Pyrrolo[2,3‐b]quinoxalines via Copper‐Free Sonogashira Coupling Reaction

A palladium‐catalyzed cascade protocol has been established for the synthesis of 4‐methyl‐1‐(1H‐pyrrolo[2,3‐b]‐quinoxalin‐2‐yl)cyclohexanols and 2‐phenyl‐1‐(1H‐pyrrolo[2,3‐b]quinoxalin‐2‐yl)propan‐1‐ols through the reaction of N‐alkyl(aryl)‐3‐chloroquinoxalin‐2‐amines with calcium carbide and cyclohexanones or 2‐phenylpropanal. This one‐pot process, carried out without any copper salt in the key step of the Sonogashira coupling reaction, provides an efficient method for the synthesis of 2,3‐disubstituted pyrrolo[2,3‐b]quinoxalines in the presence of catalytic amounts of Pd(PPh₃)₂Cl₂ in DMSO/H₂O with high yields. The benefit of this strategy is the use of a commercially available, inexpensive, and less hazardous primary chemical feedstock, calcium carbide, as an acetylene source in a wet solvent.     

Unexpected Approach to the Synthesis of 2‐Phenylquinoxalines and Pyrido[2,3‐b]pyrazines via a Regioselective Reaction

An unexpected approach to the preparation of quinoxaline and pyrido[2,3‐b]pyrazine derivatives 5 is described. The reaction between 1H‐indole‐2,3‐diones 1 , 1‐phenyl‐2‐(triphenylphosphoranylidene)ethanone ( 2 ), and benzene‐1,2‐ or pyridine‐2,3‐diamines 3 proceeds in MeOH under reflux in good to excellent yields (Scheme 1 and Table). No co‐catalyst or activator is required for this multi‐component reaction (MCR), and the reaction is, from an experimental point of view, simple to perform. The structures of 5, 5′ , and 6 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS) and were confirmed by comparison with reference compounds. A plausible mechanism for this type of reaction is proposed (Scheme 2).     

Tuning photovoltaic performance of 9,9‐dioctylfluorene‐alt‐5,7‐bis(thiophen‐2‐yl)‐2,3‐biphenylthieno[3,4‐b]pyrazine copolymeric derivatives by attaching additional donor units in pendant phenyl ring

A class of the 9,9‐dioctylfluorene‐alt‐5,7‐bis(thiophen‐2‐yl)‐2,3‐biphenylthieno [3,4‐b]pyrazine copolymeric derivatives (PFO‐3ThPz‐D) attaching additional donor (D) units in the pendant phenyl ring with a D‐A D structure was synthesized and investigated, where the additional D unit is a substituent group of fluorene, carbazole, and triphenylamine (Tpa). Their photovoltaic properties were significantly tuned by these pending donor units. Among these copolymers, the PFO‐3ThPz‐Tpa exhibited the best photovoltaic properties in the bulk heterojunction polymeric solar cells (BHJ‐PSC). The maximum power conversion efficiency (PCE) of 2.09% and the highest circuit current density (J_sc) of 7.91 mA/cm² were obtained in the cell using a blend of PFO‐3ThPz‐Tpa and PC₆₀BM (1:3, w/w) as active layer, which are 2.5 and 1.8 times higher than those corresponding levels in the other cell using the parent PFO‐3ThPz‐Ph copolymer instead of PFO‐3ThPz‐Tpa as donor, respectively. While PC₆₀BM was replaced by PC₇₀BM, the PFO‐3ThPz‐Tpa‐based BHJ‐PSC exhibited better photovoltaic properties with PCE of 3.08% and J_sc of 10.3 mA/cm². This work demonstrated that attaching donor units into the D‐A‐based copolymeric side‐chain is a simple and effective method to improve the photovoltaic properties for the resulting copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of new hetero[1,2,4]thiadiazin‐3‐one S,S‐dioxides and oxazolo[3,2‐b]hetero[1,2,4]thiadiazine S,S‐dioxides as potential psychotropic drugs

A series of 2‐substituted 2H‐thieno[3,4‐e][1,2,4]thiadiazin‐3(4H)‐one 1,1‐dioxides ( 2 ), 2‐substituted 2H‐thieno[2,3‐e][1,2,4]thiadiazin‐3(4H)‐one 1,1‐dioxides ( 3 ), 2‐substituted 4,6‐dihydropyrazolo[4,3‐e]‐[1,2,4]thiadiazin‐3(2H)‐one 1,1‐dioxides ( 4 ), 2‐substituted 2,3‐dihydrooxazolo[3,2‐b]thieno[3,4‐e]‐[1,2,4]thiadiazine 5,5‐dioxides, ( 5 ), 6‐substituted 6,7‐dihydro‐2H‐oxazolo[3,2‐b]pyrazolo[4,3‐e][1,2,4]thia‐diazine 9,9‐dioxides ( 6 ) and 7‐substituted 6,7‐dihydro‐2H‐oxazolo[3,2‐b]pyrazolo[4,3‐e][1,2,4]thiadiazine 9,9‐dioxides ( 7 ) were synthesized as potential psychotropic agents.     

A Facile Synthesis of Aryl‐Substituted Hydrazono‐Pyrazolyl[1,2,4]triazolo[3,4‐b][1,3,4][thiadiazol]‐coumarin Derivatives

Some inimitable and therapeutic coumarin‐substituted fused[1,2,4]triazolo‐[3,4‐b][1,3,4]thiadizole derivatives were synthesized by the cyclocondensation reaction of 2‐oxo‐2H‐chromene‐3‐carboxylic acid ( 1 ) and 4‐amino‐5‐hydrazinyl‐4H‐[1,2,4]‐triazole‐3‐thiol ( 2 ) by using phosphorous oxychloride as a cyclizing agent. This cyclized intermediate 3‐(3‐hydrazino‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazol‐6‐yl)‐chromen‐2‐one ( 3 ) later condensation with various ethyl 2‐(2‐arylhydrazono)‐3‐oxobutanoates ( 4 ) in NaOAc/MeOH under reflux conditions afforded the corresponding new series of aryl‐substituted hydrazono‐pyrazolyl‐[1,2,4]triazolo[3,4‐b][1,3,4][thiadiazol]‐coumarin derivatives ( 5 ) in good to excellent yields. The structures of newly synthesized compounds were established on the basis of elemental analysis, IR, ¹H NMR and mass spectroscopic studies.     

Synthesis of novel pyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidines,pyrido[3″,2″:4′,5′]thieno[3′,2′:4,5]pyrimido[l,6‐a]benzimidazoles and related fused systems

3‐Amino‐4‐aryl‐5‐ethoxycarbonyl‐6‐methylthieno[2,3‐b]pyridine‐2‐carboxamides 3a‐c were prepared from ethyl 4‐aryl‐3‐cyano‐6‐methyl‐2‐thioxo‐1,2‐dihydropyridine‐5‐carbonylates 1a‐c and reacted with some carbonyl compounds to give tetrahydropyridothienopyrimidine derivatives 6a‐c, 7a‐c and 8a‐c , respectively. Treatment of compound 3c with chloroacetyl chloride led to the formation of a next key compound, ethyl 2‐chloromethyl‐4‐oxo‐3,4‐dihydropyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidine‐8‐carboxylate 9 . Also, 3‐amino‐2‐benzimidazolylthieno[2,3‐b]pyridine‐5‐carboxylate 5 and 2‐(3′‐aminothieno [2,3‐b]pyridin‐2′‐yl)‐4‐oxo‐3,4‐dihydropyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidine‐8‐carboxylate 17 were prepared from 1c. The compounds 5, 9 and 17 were used as good synthons for other pyridothienopyrimidines and pyridothienopyrimidobenzimidazoles as well as for related fused polyheterocyclic systems.     

Synthesis of Functionalized H‐[1]Benzopyrano[2,3‐b]pyridines by the Friedländer Approach: Antimycobacterial and Antimicrobial Profile

A series of functionalized H‐[1]benzopyrano[2,3‐b]pyridine derivatives were synthesized by the Friedländer reaction of 2‐amino‐4‐oxo‐4H‐chromene‐3‐carbonitriles 1 with malononitrile, ethyl cyanoacetate, or acetophenone (Scheme). The synthesized compounds 2 – 4 were screened for their in vitro activity against antitubercular, antibacterial, and antifungal species (Fig., Table). Among the synthesized compounds, 3c and 4f were the most active with 99% inhibition against Mycobacterium tuberculosis H₃₇Rv, while compounds 2f, 3f , and 4d exhibited 69%, 63%, and 61% inhibition, respectively. The 4‐amino‐7,9‐dibromo‐1,5‐dihydro‐2,5‐dioxo‐2H‐chromeno[2,3‐b]pyridine‐3‐carbonitrile ( 3b ) showed the most potent antibacterial activity against Escherichia coli and Pseudomonas aeruginosa. Several chromeno[2,3‐b]pyridine derivatives showed equal or more potency against Staphylococcus aureus and Candida albicans.     

Aromatic Heterocycle 1,3,4‐Oxadiazole‐Substituted Thieno[3,4‐b]thiophene to Build Low‐Bandgap Polymer for Photovoltaic Application

Electron‐deficient heterocycle 1,3,4‐oxadiazole is first introduced to the 2‐position of thieno[3,4‐b]thiophene (TT) to construct a new building block 2‐(thieno[3,4‐b]thiophen‐2‐yl)‐5‐(alkylthio)‐1,3,4‐oxadiazole (TTSO) with alkylthio chain. The polymer PBDT–TTSO based on TTSO and benzodithiophene (BDT) exhibits a deep lying highest occupied molecular orbital (HOMO) energy level of −5.32 eV and low‐bandgap of 1.62 eV. The power conversion efficiency (PCE) of 5.86% is obtained with a relatively high V _OC of 0.74 V, a J _SC of 13.1 mA cm⁻², and FF of 60.5%. Furthermore, as S atom in thioether can be oxidized easily, the optoelectronic properties of PBDT–TTSO treated with different oxidants are preliminary investigated. Interestingly, the oxidation products still maintain high PCE with reduction less than 30%. This work demonstrates a new method to regulate HOMO energy levels by introducing electron‐deficient aromatic heterocyclic moiety.