Synthesis of novel 2‐(2‐methylsulfonyl‐1‐methyl‐1H‐imidazol‐5‐yl)‐5‐(alkylsulfonyl)‐1,3,4‐thiadiazoles

Starting from 5‐hydroxymethyl‐2‐mercapto‐1‐methyl‐1H‐imidazole (1), a series of 2‐(1‐methyl‐2‐methylsulfonyl‐1H‐imidazol‐5‐yl)‐5‐alkylthio and 5‐alkylsulfonyl‐1,3,4‐thiadiazole derivatives ( 9a , 9b , 9c , 9d and 10a , 10b , 10c , 10d ) were prepared as potential antimicrobial agents. The structure of the obtained compounds was confirmed by NMR, IR, Mass spectroscopy, and elemental analysis. J. Heterocyclic Chem., (2010)     

Synthesis of Novel Bis[(5‐cyanopyridin‐6‐yl)sulfanyl]butanes,Bis(2‐S‐alkylpyridines), and Bis(3‐aminothieno[2,3‐b]pyridines) Incorporating 2,6‐Dibromophenoxy Moiety

The synthetic precursors pyridine‐2(1H)‐thiones 2a , b and bis(pyridine‐2(1H)‐thione) derivative 4 , using aldehydes 1a , b incorporating 2,6‐dibromophenoxy moiety, were prepared and used to synthesize the novel target materials bis[(5‐cyanopyridin‐6‐yl)sulfanyl]butanes 5a , b , bis(2‐S‐alkylpyridines) 8a , b , and bis(3‐aminothieno[2,3‐b]pyridines) 13a–c through facile procedures. Characterization of the newly prepared compounds via elemental analyses and spectral data is established.     

Synthesis and Antifungal Screening of 2‐(2‐Aryl‐4‐methyl‐thiazol‐5‐yl)‐5‐((2‐aryl/benzylthiazol‐4‐yl)methyl)‐1,3,4‐oxadiazole Derivatives

A new series of synthesis and biological screening of 2‐(2‐aryl‐4‐methyl‐thiazol‐5‐yl)‐5‐((2‐aryl/benzylthiazol‐4‐yl)methyl)‐1,3,4‐oxadiazole derivatives 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i was achieved by condensation of 2‐(2‐aryl/benzylthiazol‐4‐yl)acetohydrazide 2a , 2b , 2c with 4‐methyl‐2‐arylthiazole‐5‐carbaldehyde 3a , 3b , 3c followed by oxidative cyclization of N'‐((4‐methyl‐2‐arylthiazol‐5‐yl)methylene)‐2‐(2‐aryl/benzylthiazol‐4‐yl)acetohydrazide 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i using iodobenzene diacetate as oxidizing agent. All the synthesized compounds were screened for their in vitro antifungal activity against Candida albicans, Candida tropicalis, Aspergillus niger, and Aspergillus flavus. Some of the synthesized compounds showed good antifungal activity.     

Synthesis,Cytotoxicity and Antibacterial Studies of Novel Symmetrically and Nonsymmetrically 4‐(Methoxycarbonyl)benzyl‐Substituted N‐Heterocyclic Carbene–Silver Acetate Complexes

From the reaction of 1H‐imidazole ( 1a ), 4,5‐dichloro‐1H‐imidazole ( 1b ), 1H‐benzimidazole ( 1c ), 1‐methyl‐1H‐imidazole ( 1d ), and 1‐methyl‐1H‐benzimidazole ( 1f ) with methyl 4‐(bromomethyl)benzoate ( 2 ), symmetrically and nonsymmetrically 4‐(methoxycarbonyl)benzyl‐substituted N‐heterocyclic carbene (NHC) precursors, 3a – 3f , were synthesized. These NHC precursors were then reacted with silver(I) acetate (AgOAc) to yield the NHC–silver acetate complexes (acetato‐κO){1,3‐bis[4‐(methoxycarbonyl)benzyl]imidazol‐2‐ylidene}silver ( 4a ), (acetato‐κO){4,5‐dichloro‐1,3‐bis[4‐(methoxycarbonyl)benzyl]‐2,3‐dihydro‐1H‐imidazol‐2‐yl}silver ( 4b ), (acetato‐κO){1,3‐bis[4‐(methoxycarbonyl)benzyl]‐2,3‐dihydro‐1H‐benzimidazol‐2‐yl}silver ( 4c ), (acetato‐κO){1‐[4‐(methoxycarbonyl)benzyl]‐3‐methyl‐2,3‐dihydro‐1H‐imidazol‐2‐yl}silver ( 4d ), (acetato‐κO){4,5‐dichloro‐1‐[4‐(methoxycarbonyl)benzyl]‐3‐methyl‐2,3‐dihydro‐1H‐imidazol‐2‐yl}silver ( 4e ), and (acetato‐κO){1‐[4‐(methoxycarbonyl)benzyl]‐3‐methyl‐2,3‐dihydro‐1H‐benzimidazol‐2‐yl}silver ( 4f ), respectively. The three NHC–AgOAc complexes 4a, 4c , and 4d were characterized by single‐crystal X‐ray diffraction. All compounds studied in this work were preliminarily screened for their antimicrobial activities in vitro against Gram‐positive bacteria Staphylococcus aureus, and Gram‐negative bacteria Escherichia coli using the qualitative disk‐diffusion method. All NHC–AgOAc complexes exhibited weak‐to‐medium antibacterial activity with areas of clearance ranging from 4 to 7 mm at the highest amount used, while the NHC precursors showed significantly lower activity. In addition, NHC–AgOAc complexes 4a and 4b , and 4d – 4f exhibited in preliminary cytotoxicity tests on the human renal‐cancer cell line Caki‐1 medium‐to‐high cytotoxicities with IC₅₀ values ranging from 3.3±0.4 to 68.3±1 μM .     

Synthesis and pharmacological properties of N‐substituted‐N′‐(4,6‐dimethylpyrimidin‐2‐yl)‐thiourea derivatives and related fused heterocyclic compounds

A series of new N‐Substituted‐N′‐(4,6‐dimethylpyrimidin‐2‐yl)‐thiourea derivatives ( 3a , 3b , 3c , 3d ) and related fused heterocyclic compounds ( 4a , 4b , 4c , 4d ) were synthesized using tetrabutylammonium bromide as phase transfer catalyst (PTC). N‐[(2E)‐5,7‐dimethyl‐2H‐[1,2,4] thiadiazolo [2,3‐a] pyrimidin‐2‐ylidene] derivatives ( 4a , 4b , 4c , 4d ) were prepared by oxidative cyclization of 3a , 3b , 3c , 3d . The structures of these novel compounds were characterized by IR, ¹H NMR, ¹³C NMR, mass spectrometry, and the elemental analysis. The crystal structures were determined from single crystal X‐ray diffraction data. The results indicated that the compounds possessed a broad spectrum of activity against the tested microorganisms and showed higher activity against fungi than bacteria. Compounds 3d and 3a exhibited the greatest antimicrobial activity. J. Heterocyclic Chem., 2011.     

Synthesis and Reactivity of 3‐oxoprop‐1‐en‐1‐olate Derivative as a Building Block for the Synthesis of Azole and Azine Derivatives

Several new heterocyclic compounds such as 7‐substituted pyrazolo[1,5‐a ]pyrimidine ( 5a–e ) derivatives have been synthesized by the reactions of the versatile unreported sodium 3‐(4‐methyl‐2‐(4‐methylphenylsulfonamido)thiazol‐5‐yl)‐3‐oxoprop‐1‐en‐1‐olate (2) with amino heterocyclic ( 3a–e ) derivatives. Reaction of (2) with hydrazonyl halide ( 7a–d ) and hydroximoyl chloride ( 11a,b ) derivatives followed by reaction with hydrazine hydrate afforded pyrazolo[3,4‐d ]pyridazine and isoxazolo[3,4‐d ]pyridazine derivatives, respectively incorporating a thiazole moiety have been described. All newly synthesized compounds were elucidated by considering the data of both elemental and spectral analysis.     

Synthesis and characterization of a series of 1,x‐bis‐(4‐oxo‐3,4‐dihydro‐1,2,3‐benzotriazin‐3‐yl)alkanes

Reaction of isatoic anhydride with an alkanediamine in DMF solution under mild conditions affords excellent yields of the 1,x‐bis‐{(2‐aminobenzoyl‐)amino}alkanes ( 2a‐k ), which have been characterized by IR and NMR spectroscopy, high resolution mass spectrometry and elemental analysis. Diazotization of the bis‐{(2‐aminobenzoyl‐)‐amino}alkanes in aqueous solution gives high yields of the 1,x‐bis‐(4‐oxo‐3,4‐dihydro‐1,2,3‐benzotriazin‐3‐yl)alkanes ( 1a‐k ), whch have also been characterized by IR and NMR spectroscopy, high resolution mass spectrometry and elemental analysis. The alkanediamines employed are as follows: ethylene diamine, 1,3‐propanediamine, 1,2‐propanediamine, 2‐methyl‐1,2‐propanediamine, 2,2‐dimethyl‐1,3‐propanediamine, 2‐hydroxy‐1,3‐propanediamine, 1,4‐diaminobutane, 1,5‐diaminopentane, 1,3‐diaminopentane (DYTEK® EP diamine), 1,6‐diaminohexane and 1,7‐diaminoheptane. The alternative method of synthesis of the bis‐(4‐oxo‐3,4‐dihydro‐1,2,3‐benzotriazin‐3‐yl)alkanes ( 1 ) via the diazonium salt from methyl anthranilate was explored.     

Synthesis of 5‐chloro‐2‐methyl‐3‐(5‐methylthiazol‐2‐yl)‐4(3H)‐quinazolinone and related compounds with potential biological activity

Eight new 2‐methyl‐4(3H)‐quinazolinones (8a‐8d, 9c, 9d, 10c, 10d) with one or two chlorine atoms in the benzene ring and a 5‐methyl‐1,3‐thiazol‐2‐yl, 4‐methyl‐1,3‐thiazol‐2‐yl, and 5‐ethyl‐1,3,4‐thiadiazol‐2‐yl substituent in position 3 of the heterocyclic ring were synthesized and characterized. The two step procedure (Scheme 1) utilizes chlorosubstituted anthranilic acids (3a‐3d) and acetic anhydride as the starting materials, with the respective chlorosubstituted 2‐methyl‐4H‐3,1‐benzoxazin‐4‐ones (4a‐4d) as the intermediates. The quinazoline derivatives were characterized by their melting points, elemental analyses and the mass, ultraviolet, infrared, and ¹H and ¹³C nmr spectra. The new compounds are expected to be biologically active.     

Synthesis,Characterization, and Antibacterial Activity of Novel (1H‐Benzo[d]imidazole‐2‐yl)‐6‐(diethylamino)‐3H‐one‐xanthene,Phenoxazine, and Oxazine

A series of novel (1H‐benzo[d]imidazole‐2‐yl)‐6‐(diethylamino)‐3H‐one‐xanthene, phenoxazine, and oxazine derivatives have been synthesized from 2‐(2′,4′‐dihydroxyphenyl) benzimidazole intermediate. Synthesized compounds 8a , 8b , 8c , 8d are fluorescent in solution, photophysical properties of compounds were studied and results revealed that compounds absorb and emit in UV–visible region with good fluorescence quantum yield. Synthesized compounds are thermally stable up to 300°C. The antibacterial activities of the synthesized compounds were studied by the well‐diffusion method. Escherichia coli (ATTC‐25922), Staphylococcus aureus (ATCC‐25923), Micrococcus (ATCC‐4698), and Bacillus subtilis (ATCC‐55422) were used to investigate the antibacterial activities.     

Novel Bis(2‐(5‐((5‐phenyl‐1H‐tetrazol‐1‐yl)methyl)‐4H‐1,2,4‐triazol‐3‐yl)phenoxy)Alkanes: Synthesis and Characterization

In this study, 10 different substituted aromatic bis‐benzaldehydes were synthesized by treating hydroxy benzaldehydes with various dihaloalkanes. Bis aldehydes 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j were treated with 2‐(5‐phenyl‐1H‐tetrazole‐1‐yl)acetohydrazide ( 3 ) in acidic medium and in the presence of ammonium acetate to yield a series of new isomeric bis(2‐(5‐((5‐phenyl‐1H‐tetrazol‐1‐yl)methyl)‐4H‐1,2,4‐triazol‐3‐yl)phenoxy)alkanes ( 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j ) in excellent to good yield. The newly synthesized compounds were characterized by the available spectroscopic analysis.     

Synthesis and Antimicrobial Activity of N‐[(2Z)‐3‐(4,6‐Substitutedpyrimidin‐2‐yl)‐4‐phenyl‐1,3‐thiazol‐2(3H)‐ylidene]‐3, 5‐dinitrobenzamide Analogues

In this study, we have synthesized 1‐(4,6‐disubstitutedpyrimidin‐2‐yl)‐3‐(3,5‐dinitrobenzoyl)‐thiourea derivatives ( 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h ) and N‐[(2Z)‐3‐(4,6‐disubstitutedpyrimidin‐2‐yl)‐4‐phenyl‐1,3‐thiazol‐2(3H)‐ylidene]‐3, 5‐dinitrobenzamide ( 2a‐2h ) analogues and characterized by IR spectroscopy, NMR spectroscopy, elemental analysis, and single crystal X‐ray diffraction data. The compounds ( 2a‐2h ) were screened for antimicrobial activity against Gram positive, Gram negative, and fungal species. The results of antimicrobial study indicated that compounds showed most potential and appreciable antibacterial and antifungal activities.     

A convenient synthesis of novel 7‐phosphonylbenzyl‐2‐substituted pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]‐pyrimidine derivatives

A series of pyrazolo[4,3‐e]‐1,2,4‐triazolo‐[1,5‐c]pyrimidine derivatives, bearing phosphonylbenzyl chain in position 7, were conveniently synthesized in an attempt to obtain potent and selective antagonists for the A_2A adenosine receptor or potent pesticide lead compounds. Diethyl[(5‐amino‐4‐cyano‐3‐methylsulfanyl‐pyrazol‐1‐yl)‐benzyl]phospho‐nate ( 3 ), which was prepared by the cyclization of diethyl 1‐hydrazinobenzylphosphonate ( 1 ) with 2‐[bis(methylthio)methylene]malononitrile ( 2 ), reacted with triethyl orthoformate to afford diethyl[(4‐cyano‐5‐ethoxymethyleneamino‐3‐methylsulfanyl‐pyrazol‐1‐yl)‐benzyl]phosphonate ( 4 ), which reacted with various acyl hydrazines in refluxing 2‐methoxyethanol to give the target compounds 5a–h in good yields. Their structures were confirmed by IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis. The crystal structure of 5e was determined by single crystal X‐ray diffraction © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:634–638, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20478     

Quinolone Analogs 14: Synthesis of Antimalarial 1‐Aryl‐3‐(4‐quinolon‐2‐yl)ureas and Related Compounds

The 4‐quinolone‐2‐carbohydrazide 6a was converted into 1‐aryl‐3‐(4‐quinolon‐2‐yl)ureas 5a , 5b , 5c , 5d , 5e , 1‐aryl‐3‐(4‐quinolon‐2‐yl)imidazolidine‐2,4‐diones 9a , 9b , and N‐(4‐quinolon‐2‐yl)carbamates 10a , 10b via 4‐quinolone‐2‐carbonylazide 7a . The 4‐methoxyquinoline‐2‐carbohydrazide 6b was also transformed into 1‐aryl‐3‐(4‐methoxyquinolin‐2‐yl)ureas 11a , 11b , 11c , 11d , 1‐aryl‐3‐(4‐methoxyquinolin‐2‐yl)imidazolidine‐2,4‐diones 12a , 12b , and N‐(4‐methoxyquinolin‐2‐yl)carbamates 13a , 13b via 4‐methoxyquinoline‐2‐carbonylazide 7b . Some of the 1‐aryl‐3‐(4‐quinolon‐2‐yl)ureas 5a , 5b , 5c , 5d , 5e showed the in vitro antimalarial activity to chloroquine‐resistant Plasmodium falciparum, wherein IC₅₀ was 0.93 to 4.00 μM.     

An Innovative Protocol for the Synthesis of 3‐(Pyridin‐2‐yl)‐5‐sec‐aminobiphenyl‐4‐carbonitriles and 9,10‐Dihydro‐3‐(pyridine‐2‐yl)‐1‐sec‐aminophenanthrene‐2‐carbonitriles

Herein, we present an innovative, novel, and highly convenient protocol for the synthesis of 3‐(pyridin‐2‐yl)‐5‐sec‐aminobiphenyl‐4‐carbonitriles ( 6a , 6b , 6c , 6d , 6e , 6f , 6g ) and 9,10‐dihydro‐3‐(pyridine‐2‐yl)‐1‐sec‐aminophenanthrene‐2‐carbonitriles ( 10a , 10b , 10c , 10d , 10e ), which have been delineated from the reaction of 4‐sec‐amino‐2‐oxo‐6‐aryl‐2H‐pyran‐3‐carbonitrile ( 4a , 4b , 4c , 4d , 4e , 4f , 4g ) and 4‐sec‐amino‐2‐oxo‐5,6‐dihydro‐2H‐benzo[h]chromene‐3‐carbonitriles ( 9a , 9b , 9c , 9d , 9e ) with 2‐acetylpyridine ( 5 ) through the ring transformation reaction by using KOH/DMF system at RT. The salient feature of this procedure is to provide a transition metal‐free route for the synthesis of asymmetrical 1,3‐teraryls like 3‐(pyridin‐2‐yl)‐5‐sec‐aminobiphenyl‐4‐carbonitriles ( 6a , 6b , 6c , 6d , 6e , 6f , 6g ) and 9,10‐dihydro‐3‐(pyridine‐2‐yl)‐1‐sec‐aminophenanthrene‐2‐carbonitriles ( 10a , 10b , 10c , 10d , 10e ). The novelty of the reaction lies in the creation of an aromatic ring from 2H‐pyran‐2‐ones and 2H‐benzo[h]chromene‐3‐carbonitriles via two‐carbon insertion from 2‐acetylpyridine ( 5 ) used as a source of carbanion.     

Synthesis of Novel 3‐(3‐(5‐Methylisoxazol‐3‐yl)‐7H‐[1,2,4]Triazolo [3,4‐b][1,3,4]Thiadiazin‐6‐yl)‐2H‐Chromen‐2‐Ones

A novel series of coumarin substituted triazolo‐thiadiazine derivatives were designed and synthesized by using 5‐methyl isoxazole‐3‐carboxylic acid ( 1 ), thiocarbohydrazide ( 2 ), and various substituted 3‐(2‐bromo acetyl) coumarins ( 4a , 4b , 4c , 4e , 4d , 4f , 4g , 4h , 4i , 4j ). Fusion of 5‐methyl isoxazole‐3‐carboxylic acid with thiocarbohydrazide resulted in the formation of the intermediate 4‐amino‐5‐(5‐methylisoxazol‐3‐yl)‐4H‐1,2,4‐triazole‐3‐thiol ( 3 ). This intermediate on further reaction with substituted 3‐(2‐bromo acetyl) coumarins under simple reaction conditions formed the title products 3‐(3‐(5‐methylisoxazol‐3‐yl)‐7H‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazin‐6‐yl‐2H‐chromen‐2‐ones ( 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j ) in good to excellent yields. All the synthesized compounds were well characterized by physical, analytical, and spectroscopic techniques.     

One‐Pot Syntheses of 2‐(2‐Sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic Acid Derivatives via Reactions of 3‐(2‐Isothiocyanatophenyl)prop‐2‐enoic Acid Derivatives with Thiols or Sodium Sulfide

Two efficient methods for the preparation of 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 3 under mild conditions have been developed. The first method is based on the reaction of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoates 1a – 1c with thiols in the presence of Et₃N in THF at room temperature, leading to the corresponding dithiocarbamate intermediates 2 , which underwent spontaneous cyclization at the same temperature by an attack of the S‐atom at the prop‐2‐enoyl moiety in a 1,4‐addition manner (Michael addition) to give 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetates in one pot. The second method involves treatment of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoic acid derivatives 1b – 1d with Na₂S leading to the formation of 2‐(2‐sodiosulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid intermediates 5 by a similar addition/cyclization sequence, which are then allowed to react with alkyl or aryl halides to afford derivatives 3 . 2‐(2‐Thioxo‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 6 can be obtained by omitting the addition of halides.     

Study of 1,3‐Dipolar Cycloaddition and Ring Contraction of New 1,4‐Phenylene‐bis[1,5]benzothiazepine Derivatives

Some 1,4‐phenylene‐bis[1,2,4]oxadiazolo‐[5,4‐d][1,5]benzothiazepine derivatives ( 4a , 4b , 4c ) were synthesized by 1,3‐dipolar cycloaddition reaction of benzohydroximinoyl chloride with 1,4‐phenylene‐bis(4‐aryl)‐2,3‐dihydro[1,5]benzothiazepine ( 2a , 2b , 2c ); meanwhile, compounds 2a , 2b , 2c also occurred ring contraction under acylating condition to obtain bis[2‐aryl‐2′‐(β‐1,4‐phenylenevinyl)‐3‐acetyl]‐2,3‐dihydro[1,5]benzothiazoles ( 3a , 3b , 3c ). The structures of some novel compounds were confirmed by IR, ¹H‐NMR, elemental, and X‐ray crystallographic analysis.     

Synthesis and Biological Activity of 1‐(Substituted phenoxyacetoxy)‐1‐(pyridin‐2‐yl or thien‐2‐yl)methylphosphonates

A series of novel O,O‐dimethyl 1‐(substituted phenoxyacetoxy)‐1‐(pyridin‐2‐yl or thien‐2‐yl)methylphosphonates 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j , 6k , 6l , 6m , 6n and 7a , 7b , 7c , 7d were synthesized. Their structures were confirmed by IR, ¹H NMR, mass spectroscopy, and elemental analyses. The results of preliminary bioassays show that some of the title compounds exhibit moderate to good herbicidal and fungicidal activities. For example, the title compounds 6a , 6c , 6l , 6m , and 7d possess 90–100% inhibition against most of the tested plants at the dosage of 1500 g ai/ha, whereas the title compounds 6b , 6g , 6h and 6n possess 92–100% inhibition against Fusarium oxysporum, Phyricularia grisea, Botrytis cinereapers, Gibberella zeae, Sclerotinia sclerotiorum, and Cercospora beticola at the concentration of 50 mg/L.     

Synthesis and Spectral Characterization of Novel Bis‐thiazole Derivatives via Ring Closure of Benzo[d]thiazol‐2‐amine,Various α‐Haloketones,and S‐Nucleophiles

Novel functionalized bis‐thiazole derivatives ( 4a–d , 9a , b , 13a–e , and 16a–d ) were synthesized in good to excellent yields (70–90%) via the ring closure of benzo[d ]thiazol‐2‐amine and various α‐haloketones in the presence of carbon disulfide or aryl isothiocyanates as S‐nucleophiles. The structures of newly synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, elemental analysis, and mass spectroscopy techniques.     

Synthesis and Photovoltaic Properties of Thieno[3,4‐c]pyrrole‐4,6‐dione‐based donor–acceptor Copolymers

Three donor–acceptor (D–A) 1,3‐di(thien‐2‐yl)thieno [3,4‐c]pyrrole‐4,6‐dione‐based copolymers, poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, poly{N‐(1‐octylnonyl)carbazole‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, and poly {4,8‐bis(2‐ethylhexyloxyl) benzo[1,2‐b:3,4‐b′]dithiophene‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c] pyrrole‐4,6‐dione} were synthesized by Suzuki or Stille coupling reaction. By changing the donor segment, the bandgaps and energy levels of these copolymers could be finely tuned. Cyclic voltammetric study shows that the highest occupied molecular orbital (HOMO) energy levels of the three copolymers are deep‐lying, which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open‐circuit potential when they are used in photovoltaic cells. Bulk‐heterojunction photovoltaic cells were fabricated with these polymers as the donors and PC₇₁BM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.22, 0.74, and 3.11% with large open‐circuit potential of 1.01, 0.99, and 0.90 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012