Free radical 4‐nitrophenylation of thieno[2,3‐b]pyridine. Part 1: General experimental procedure and prediction of isomeric ratios of products

Thieno[2,3‐b]pyridine (1) was warmed at 45 ± 7° with diazotized 4‐nitroaniline ( 2 ) (molar ratio 1:2 = 3.6:1) in buffered (sodium acetate‐acetic acid) aqueous solution until gas evolution ceased. The reaction mixture was separated into these fractions: (a) water‐soluble (discarded), (b) acetone‐soluble (tars), (c) ether‐soluble, and (d) ether‐ and chloroform‐soluble, but acetone‐insoluble (rust‐colored solids, Y , 12% yield as 4‐nitrophenyl‐ 1 isomers, 3 ). Fractional evaporative distillations of (b) and (c) gave recovered 1 (69%) and yellow‐red sublimates (Z, 20% yield as 3 ). Y and Z were handled separately for isolation and identification of isomers [2]. Three general methods for predicting the isomeric ratios of 3 which one should obtain are presented, viz. (1) an amalgamation of reported free‐radical phenylation results for quinoline and benzo[b]thiophene, (2) calculations of Frontier Radical Densities for positions 2‐6 only, and (3) Molecular Orbital calculations for electron densities and superdelocalizabilities for free‐radical attack at positions 1‐7, as modified by a proposed rearrangement of the attacking group from the heteroatomic N and S positions to adjacent alpha positions.     

Free‐radical 4‐nitrophenylation of thieno[2,3‐b]pyridine. Part 3: Consideration of mechanistic and selectivity factors involved in the substitution process

A 1:1 geometrically oriented encounter complex between thieno[2,3‐b]pyridine (1) and 4‐nitrophenyldia‐zoacetate (2) is proposed to account for the dominant formation (ca. 64%) of the 2‐isomer in the mixture of 4‐nitrophenyl‐l isomers obtained previously. A mechanism involving one‐electron transfer from 1 to 2 plus fragmentation of 2· into 4‐nitrophenyl free radical, N₂, and acetate ion is invoked. Formation of other isomers is discussed. It is noted that there is a close correlation between orientational rules plus mechanisms of reaction for numerous free‐radical substitutions (S_R) with S_N reactions of alkyllithiums on furan, thiophene, N‐alkylpyrroles, pyridine, and their condensed aromatic molecules, including 1, as substrates. Also isomeric selectivities for S_E, S_N, and S_R substitutions into 1 were shown to be qualitatively consistent with one another. While S_E reactions occur largely at position 3 and then at 2, S_N and S_R reactions occur either at 2 or 6. Selectivity for positions 4 or 5 is small or zero.     

Synthesis of new derivatives of thieno[2,3‐b]pyridine fused with octyl ring

Derivatives of thiophene, thieno[2,3‐b]pyridine, thieno[5′,4′:4,5]pyrimido[3,2‐a]pyridine and thiepine fused with octyl ring have been synthesized and tested for antimicrobial and antifungal activities. The structure of the newly synthesized compounds have been established on the basis of their analytical and spectral data.     

An Efficient Synthesis and Fluorescent Properties of Pyrazole[3,4‐b]thieno[2,3‐e]pyridine Derivatives

A simple and efficient method for the synthesis of pyrazole[3,4‐b]thieno[2,3‐e]pyridine derivatives via the sequence of three‐component, catalyst‐free, and solvent‐free condensation and oxidation was described. The products feature a donor‐π‐conjugated acceptor fluorescent activity system, and the fluorescence emission wavelength was measured in methanol. Some products were fluorescent in solution emitting at blue light (λ_em = 430–505 nm).     

Novel synthesis of thieno[2,3‐b]pyridine and substituted 2‐thienylthiourea derivatives as antibiotic agents

Derivatives of thieno[2,3‐b]pyridine, 2‐thienylthiourea, 2‐thienylurea, 2‐thienylacetamide incorporating the 2‐phthalimidomethyl moiety have been synthesized. The synthesized compounds were then investigated for antibacterial activity against Escherichia coli, Bacillus subtilis and Staphylococcus aureus. The compounds were also investigated for antifungal activity against Aspergillus niger and Fusarium oxysporium. The structures of the newly synthesized compounds have been established on the basis of their analytical and spectral data.     

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).     

Synthesis of thieno[2,3‐b][1,5]benzoxazepine derivatives

A new series of 4‐(4‐methylpiperazin‐1‐yl)thieno[2,3‐b][1,5]benzoxazepines 1a‐k has been synthesized from 4‐bromo‐2‐methylthiophene 6 or ethyl 2‐amino‐4,5‐dimethyl‐3‐thiophencarboxylate 10 . Preparation of the key intermediate thieno[2,3‐b][1,5]benzoxazepine‐4(5H)‐ones 4a‐i, 4k were carried out by treatment of 2‐bromo‐N‐(2‐hydroxyphenyl)‐3‐thiophencarboxamides 5a‐i, 5k with potassium carbonate in DMSO. Compounds 1 are thienoanalogues of loxapine, a potent antipsychotic drug. Of these compounds, the neu‐roleptic activity of 2‐methyl‐4‐(4‐methylpiperazin‐l‐yl)thieno[2,3‐b][1,5]benzoxazepine 1a (R¹, R³=H, R²=CH₃) demonstrated potent antipsychotic activity.     

Synthesis and mutagenic potency of structural isomers of 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine

Synthesis of 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP), three structural isomers, and two desphenyl PhIP congeners has been carried out. Mutagenic potency was evaluated using S. typhimurium strain TA98 in the Ames test. Mutagenic potency increased in relation to structural features in these heterocyclic amines that allow extended resonance between the phenyl and imidazo[4,5‐b]pyridine N²‐amino substituents. By contrast, PhIP isomers, whose substitution disallows involvement of the phenyl group in their aminoimidazo resonance hybrids, and desphenyl congeners were from 86‐ to 234‐fold less mutagenic than PhIP.     

Base‐catalyzed condensation of thioglycolic ester with β‐chloropyrrolecarbaldehyde: One‐pot approach to substituted thieno[2,3‐b]pyrroles

A simple methodology has been developed for the synthesis of thieno[2,3‐b]pyrroles from N‐aryl‐diformylated‐pyrroles by base catalyzed condensation with thioglycolic ester. J. Heterocyclic Chem., 2011.     

A facile synthesis of new thieno[2,3‐b][1,4]thiazine derivatives starting from 2‐acylamino‐3,3‐dichloroacrylonitriles

Readily available 2‐acylamino‐3,3‐dichloroacrylonitriles are sequentially treated with methyl mercaptoacetate in the presence of sodium methylate and with sulfuric acid to furnish the methyl ester of 7‐amino‐2‐oxo‐3H‐thieno[2,3‐b][1,4]thiazine‐6‐carboxylic acid. Treating it first with triethyl orthoformate and then with ammonia or primary amines, the pyrimidine‐4‐one nucleus is annelated to the thienothiazine system, which is corroborated by spectroscopic methods and X‐ray diffraction analysis. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:411–415, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20232     

Synthesis and antitumor evaluation of some new derivatives and fused heterocyclic compounds derived from thieno[2,3‐b]pyridine

On the basis of the proven activity of thieno[2,3‐b]pyridines as anticancer, we have designed to synthesize a novel several heterocyclic compounds utilizing thieno[2,3‐b]pyridine as a skeleton through various chemical reactions. The synthesized compounds bear rings that are either directly attached to the thieno[2,3‐b]pyridine as in compounds 4 to 6 and 9 or connected through an amide bridge as compounds 2 , 3a ‐ b , 7 , and 8 . As well as, compounds 10 , 12 to 28 , 30 , 31 , and 33 to 36 bear fused rings to the thieno[2,3‐b]pyridine backbone. The newly synthesized compounds were screened for their antiproliferative activity in vitro against hepatocellular carcinoma (HepG‐2) and breast cancer (MCF‐7) compared with the standard drug (doxorubicin). Compounds 3b , 4 , 6 , 22 , and 28 exhibited promising growth inhibitory effect toward both HepG‐2 and MCF‐7 cell lines with IC₅₀ values ranging from 5.88 to 11.70 μg/mL and 9.64 to 15.10 μg/mL, respectively.     

Synthesis and Reactions of Some New Heterocyclic Compounds Containing Cycloalka[e]thieno[2,3‐b]pyridine Moiety

Hydrolysis of ethyl 3-amino-4-aryl-cycloalka[e]thieno[2,3-b]pyridine-2-carboxylates ( 3a-d) gave the corresponding o-aminocarboxylic acids 4a-d . Heating the latter compounds ( 4a-d) with acetic anhydride furnished the oxazinone derivatives 5a-d which, in turn, underwent recyclization reaction to give the corresponding pyrimidinones 6a-d upon treatment with ammonium acetate in acetic acid. Reaction of 3-amino-4-aryl-cycloalka[e]thieno[2,3-b]pyridine-2-carboxamides ( 3f,h ) with triethyl orthoformate gave pyrimidinone derivatives 7a,b . Reaction of 3-amino-4-phenyl-cycloalka[e]thieno[2,3-b]pyridine-2-carboxamides 3e,h with aromatic aldehydes furnished tetrahydropyridothienopyrimidinones 8a-d . Chlorination of 7a,b and 6a-d by using phosphorous oxychloride produced 4-chlorocycloalka[5′,6′]pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidine derivatives 9a-f which were used as key intermediates in the synthesis of several new cycloalkapyrido-thienopyrimidines 10a-f ˜ 14a-f . Moreover, some cycloalkapyridothienotriazinones 15a,b-17a,b were synthesized.     

A structural systematic study of three isomers of difluoro‐N‐(4‐pyridyl)benzamide

The isomers 2,3‐, (I), 2,4‐, (II), and 2,5‐difluoro‐N‐(4‐pyridyl)benzamide, (III), all with formula C₁₂H₈F₂N₂O, all exhibit intramolecular C—H...O=C and N—H...F contacts [both with S(6) motifs]. In (I), intermolecular N—H...O=C interactions form one‐dimensional chains along [010] [N...O = 3.0181 (16) Å], with weaker C—H...N interactions linking the chains into sheets parallel to the [001] plane, further linked into pairs via C—H...F contacts about inversion centres; a three‐dimensional herring‐bone network forms via C—H...π(py) (py is pyridyl) interactions. In (II), weak aromatic C—H...N(py) interactions form one‐dimensional zigzag chains along [001]; no other interactions with H...N/O/F < 2.50 Å are present, apart from long N/C—H...O=C and C—H...F contacts. In (III), N—H...N(py) interactions form one‐dimensional zigzag chains [as C(6) chains] along [010] augmented by a myriad of weak C—H...π(arene) and O=C...O=C interactions and C—H...O/N/F contacts. Compound (III) is isomorphous with the parent N‐(4‐pyridyl)benzamide [Noveron, Lah, Del Sesto, Arif, Miller & Stang (2002). J. Am. Chem. Soc. 124 , 6613–6625] and the three 2/3/4‐fluoro‐N‐(4‐pyridyl)benzamides [Donnelly, Gallagher & Lough (2008). Acta Cryst. C 64 , o335–o340]. The study expands our series of fluoro(pyridyl)benzamides and augments our understanding of the competition between strong hydrogen‐bond formation and weaker influences on crystal packing.     

Efficient one pot preparation of variously substituted thieno [2,3‐b] thiophene

An efficient one pot access to variously substituted thieno[2,3‐b]thiophene is described. The title compounds were obtained from 1,3‐dicarbonyl or equivalent compounds, carbon disulfide and halomethyl derivatives in good to high yields and fully characterized.     

Synthesis of new methylated thieno[2,3‐a] and [3,2‐b]carbazoles by reductive cyclization of 6‐(2′‐Nitrophenyl)benzo[b]thiophenes obtained by palladium‐catalyzed cross‐coupling isabel

The synthesis of new methylated thieno[2,3‐a] and [3,2‐b]carbazoles (5) (R=H) was achieved by a palladium‐catalyzed cross‐coupling, intramolecular reductive cyclization sequence of reactions. The cyclization precursors 6‐(2′‐nitrophenyl)benzo[b]thiophenes (3) were obtained by Suzuki cross‐coupling of 6‐boronated methylbenzo[b]thiophenes intermediates (2) with 2‐bromo or iodonitrobenzene. The boronated intermediates (2) were prepared via bromine‐lithium exchange followed by boron transmetalation and coupled in situ using Pd(OAc)₂ giving thus a “one‐pot” three steps reaction from the 6‐bromobenzo[b]thio‐phenes (1) to the cyclization precursors (3) . In the reductive cyclization step, N‐ethylthienocarbazoles (5) (R=Et) were also obtained. Several experiments have been made varying the amount of triethylphosphite and the time of reaction, to avoid their formation.     

A new method for the synthesis of thieno[2,3‐c]pyrazoles

A new method has been found for the synthesis of pyrazoleacetate esters from pyrazolaldehyde. By a new tandem reaction, in which methyl 4‐pyrazoleacetate was reacted with carbon disulfide and iodomethane, thieno[2,3‐c]pyrazole was synthesized. This was an easy method for the synthesis of this type of heterocycle. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 303–305, 1999     

Synthesis and antimalarial activity of ethyl 3‐amino‐4‐oxo‐9‐(phenylsubstituted)thieno[2,3‐b]quinoline‐2‐carboxylate derivatives

A series of thieno[ 2 ,3‐b]quinolone derivatives were synthesized and investigated for their abilities to inhibit β‐hematin formation, hemoglobin hydrolysis and in vivo for their efficacy in rodent Plasmodium berghei. Compound 3b was the most promising as inhibitor of hemoglobin hydrolysis, and its effects as inhibitor of β‐hematin formation was promising. When the aromatic ring was substituted in 2 (Me), in 3 (CF₃) or in 2,4 (Cl) the inhibition of hemoglobin proteolysis was maximal (88%), the rest of compounds maintained a low inhibition. The most active compound to emerge in vitro and in murine studies, was 3b suggesting an antimalarial activity via multiple mechanisms.