Novel Rearrangement of 3‐Acylaminofuro[2,3‐b]pyridines into 3‐(oxazol‐4‐yl)pyridin‐2‐ones

3‐Acylaminofuro[2,3‐b]pyridine derivatives have been synthesized, and their behavior under acidic and basic conditions was studied. A new base‐catalyzed rearrangement of 3‐acylaminofuro[2,3‐b]pyridine derivatives into 3‐(oxazol‐4‐yl)pyridine‐2‐ones has been founded.     

Synthesis of 2,3‐Disubstituted 5‐Iodo‐1H‐Pyrrolo[2,3‐b]pyridines via Fischer Cyclization

A simple and convenient procedure for the preparation of some unknown 2,3‐disubstituted 5‐iodo‐1H‐pyrrolo[2,3‐b ]pyridines from readily available starting materials by Fischer indole cyclization in polyphosphoric acid is described. The present methodology provides an alternative synthetic approach to the synthesis of 5‐iodo‐7‐azaindole scaffold. All synthesized compounds were characterized by IR, MS, ¹H and ¹³C NMR, and elemental analysis.     

A Facile One‐Pot Synthesis of Functionalized 1,5‐Dihydro‐2H‐[1]benzopyrano[2,3‐b]pyridin‐5‐ones

The highly reactive 1 : 1 intermediate generated in the reaction between dialkyl acetylenedicarboxylate (=but‐2‐ynedioic acid dialkyl ester) 4 and triphenylphosphine was trapped by 2‐amino‐4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehydes 5 to yield highly functionalized dialkyl‐1,5‐dihydro‐5‐oxo‐1‐phenyl‐2H‐[1]benzopyrano[2,3‐b]pyridine‐2,3‐dicarboxylates in high yield.     

The Synthesis of New Benzo[h]thieno[2,3‐b]quinoline‐9‐yl(aryl)methanone Derivatives

Novel derivatives of benzo[h ]thieno[2,3‐b ]quinoline‐9‐yl(aryl)methanone were synthesized in good yield and short reaction times by reaction of 2‐mercaptobenzo[h ]quinoline‐3‐carbaldehyde with phenacyl bromides under basic conditions. All compounds were characterized using Fourier transform infrared, ¹H nuclear magnetic resonance and ¹³C nuclear magnetic resonance, spectral data, and elemental analysis.     

Synthesis of [2‐aryl‐6‐oxo‐6H‐chromeno[6,7‐d]oxazol‐8‐yl]‐acetic acid ethyl esters

A number of coumarino[6,7‐d]oxazoles (nitrogen analogs of psoralens) have been synthesized from (7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 1 . The synthetic route began with the nitration of 1 with nitric acid in acetic acid to give (6‐nitro‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 2 ; (3,6‐dinitro‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 3 and (3,6,8‐trinitro‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 4 . The reduction of 2 was accomplished with tin(II) chloride, tin, and concentrated hydrochloric acid in ethanol giving (6‐amino‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 5 . After the condensation of aminocoumarin 5 with aromatic aldehyde in glacial acetic acid medium, followed the dehydrocyclization to coumarino[6,7‐d]oxazoles 7a‐k . The intermediate Schiff's bases 6a‐k have been obtained from 5 with aromatic aldehyde in ethanol. Antibacterial and antifungal activities of the compounds have been evaluated.     

Regio‐ and stereoselective synthesis of 1‐benzopyrano[2,3‐b]pyrrolo[2,3‐d]pyridines: A microwave‐accelerated intramolecular [3+2] cycloaddition reaction of azomethine ylide

Regio‐ and stereoselective syntheses of tetracyclic compounds having chromone, pyrrolidine, and piperidine rings have been accomplished by an intramolecular [3+2] cycloaddition reaction involving azomethine ylide. The reactions were carried out thermally as well as by irradiation with microwave. The latter process accelerates the reaction. The selectivities were investigated by density functional theory computation. J. Heterocyclic Chem., (2011).     

1H‐Pyrrolo[2,3‐b]pyridine‐3‐acetic acid as a molecular probe for use in auxin physiology

The structural characterization of 1H‐pyrrolo­[2,3‐b]­pyridine‐3‐acetic acid (alternative name: 7‐aza­indole‐3‐acetic acid), C₉H₈N₂O₂, reveals similar molecular geometry, i.e. with the side chain perpendicular to the 7‐aza­indole ring, to that of the natural plant growth hormone indole‐3‐acetic acid (auxin) and its alkyl­ated and halogenated derivatives.     

Facile preparation of benzo[4,5]thieno[2,3-b]pyridines and naphtho[b-4,5]thieno[2,3-b]pyridines via the reaction of Barton esters and benzynes

Titled compounds were prepared in a one-pot synthesis by generating symmetrically substituted benzyne intermediates by the diazotization of anthranilic acids in the presence of Barton esters. Unsymmetrically substituted aryne either gave mixtures of regioisomers or failed. However, nitro and methyl derivatives of titled compounds could be obtained as single products using appropriately substituted Barton esters.     

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 substituted 3‐(5‐amino‐[1,3,4]thiadiazol‐2‐yl)‐2H‐pyrano[2,3‐c]pyridin‐2‐ones

An efficient two‐step synthesis of novel 3‐(5‐amino‐[1,3,4]thiadiazol‐2‐yl)‐2H‐pyrano[2,3‐c]pyridine‐2‐ones was developed. In the first step, a new 2H‐pyrano[2,3‐c]pyridine‐3‐carboxamide 5 was prepared by Knoevenagel condensation of pyridoxal hydrochloride with cyanoacetamide. In the second step, the reaction of carboxamide 5 with a series of N⁴‐substituted thiosemicarbazides yielded a library of 35 dis crete compounds 8 {1–35} in high yields. The intermolecular recyclization mechanism leading to these products is discussed.     

Five (1H‐pyrrol‐2‐yl)­pyridines

The title (1H‐pyrrol‐2‐yl)­pyridines, C₉H₈N₂, substituted at the ortho, meta, and para positions of the pyridine ring all have hydrogen‐bonded arrangements with geometrically similar, nearly linear, N(pyrrole)—H⋯N(pyridine) hydrogen bonds of average length. The graph sets for the ortho, meta, and three para polymorphs are R(10), C(6), C(7), C(7), and R(28), respectively.     

A convenient synthesis of 2‐Arylidene‐5H‐thiazolo[2,3‐b]quinazo‐line‐3,5[2H]‐diones and their benzoquinazoline derivatives

Various 5H‐thiazolo[2,3‐b]quinazoline‐3,5[2H]‐diones (7a,b), 2‐arylidene‐5H‐thiazolo[2,3–b]quin‐azoline‐3,5[2H]‐diones ( 9a‐o ) and 2‐arylidene‐5H‐thiazolo[2,3‐b]benzoquinazoline‐3,5[2H]‐diones ( 12a,b ) have been synthesized via simple and efficient methods.     

A convenient synthesis of 2‐(1H‐1,2,4‐triazol‐1‐yl)‐2H‐1,4‐benzothiazine derivatives

A series of 2‐(1H‐1,2,4‐triazol‐1‐yl)‐2H‐1,4‐benzothiazines were designed and synthesized by condensation of 1,2,4‐triazole‐substituted ω‐bromoacetophenones and o‐aminothiophenols with the aid of K₂CO₃ under mild conditions with moderate to high yields. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:332–336, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20434     

Synthesis of Novel 1‐(Benzo[d]thiazol‐2‐yl)‐1H‐pyrrol‐2(5H)‐ones

The titled products comprising of two mutually merged bioactive nucleuses, 2‐aminobenzo[d]thiazole and 2,5‐dihydropyrrole rings, were obtained from the reaction between dialkyl acetylenedicarboxylates and alkyl 2‐(benzo[d]thiazol‐2‐yl)amino‐2‐oxoacetates in the presence of triphenylphosphine at RT.     

2‐[2‐(Pyrrolidin‐2‐yl)propan‐2‐yl]‐1H‐pyrrole and its amide derivative 1‐{2‐[2‐(1H‐pyrrol‐2‐yl)propan‐2‐yl]pyrrolidin‐1‐yl}ethanone

In the title compounds, C₁₁H₁₈N₂, (II), and C₁₃H₂₀N₂O, (III), the pyrrolidine rings have twist conformations. Compound (II) crystallizes with two independent molecules (A and B) in the asymmetric unit. The mean planes of the pyrrole and pyrrolidine rings are inclined to one another by 89.99 (11) and 89.35 (10)° in molecules A and B, respectively. In (III), the amide derivative of (II), the same dihedral angle is much smaller, at only 13.42 (10)°. In the crystal structure of (II), the individual molecules are linked via N—H...N hydrogen bonds to form inversion dimers, each with an R²₂(12) graph‐set motif. In the crystal structure of (III), the molecules are linked via N—H...O hydrogen bonds to form inversion dimers with an R²₂(16) graph‐set motif.     

A convenient route to α-amido-β-lactams

Dedicated to Professor John C. Sheehan on the occasion of his sixty-fifth birthday. A method for the synthesis of α-amido-β-lactams without the intermediacy of an α-amino-β-lactam is described. The appropriate β-keto ester is used for preparing a vinylamino β-lactam via a “Dane salt” by a previously reported method. Oxidation with ruthenium tetroxide and periodic acid of this product leads directly to the desired “V”, or “G” or analogous α-amido side chain.     

4,6‐Dimethyl‐2‐[(4‐phenylpiperidin‐1‐yl)methyl]isothiazolo[5,4‐b]pyridin‐3(2H)‐one and 4,6‐dimethyl‐2‐[(4‐phenyl‐1,2,3,6‐tetrahydropyridin‐1‐yl)methyl]isothiazolo[5,4‐b]pyridin‐3(2H)‐one

In the crystal structures of the title compounds, C₂₀H₂₃N₃OS, (II), and C₂₀H₂₁N₃OS, (III), significant differences occur in the conformation of, respectively, the phenylpiperidine and phenyltetrahydropyridine substituents at the 2‐position of the isothiazolopyridine system. The piperidine ring adopts a chair conformation, while the tetrahydropyridine ring assumes a half‐chair form. The phenylpiperidine and phenyltetrahydropyridine fragments exhibit different conformations resulting from the steric and conjugation effects in the phenyl ring, respectively. Theoretical calculations show that both conformations are energetically stable and correspond to a minimum of energy for the analyzed systems. The molecular packing in (II) is influenced by π–π interactions of the isothiazolopyridine systems, with a shortest centroid‐to‐centroid separation of 3.5843 (11) Å between pyridine rings. In the crystal structure of (III), the molecules are linked by C—H...O hydrogen bonds and C—H...π interactions.     

A convenient route to pyridones,pyrazolo[2,3‐a]pyrimidines and pyrazolo[5,1‐c]triazines incorporating antipyrine moiety

Condensation of 4‐aminoantipyrine with ethyl acetoacetate, ethyl benzoylacetate, and ethyl cyanoacetate furnished the corresponding ethyl 3‐(1,2‐dihydro‐1,5‐dimethyl‐2‐phenyl‐3‐oxo‐3H‐pyrazol‐4‐yl)aminoacrylate and 2‐cyano‐N‐[(1,2‐dihydro‐1,5‐dimethyl‐2‐phenyl‐3‐oxo‐3H‐pyrazol‐4‐yl)]acetamide derivatives. The aminoacrylates derivatives react with acetonitrile and sodium hydride to give 2‐amino‐6‐methyl‐1‐(1,2‐dihydro‐1,5‐dimethyl‐2‐phenyl‐3‐oxo‐3H‐pyrazol‐4‐yl)‐4‐pyridone. Reaction of the cyanoacetamide derivative with dimethylformamide‐dimethylacetal (DMF‐DMA) afforded 2‐cyano‐N‐[1,2‐dihydro‐1,5‐dimethyl‐2‐phenyl‐3‐oxo‐pyrazol‐4‐yl]‐2‐(N,N‐dimethylamino)methylene acetamide in high yield. Treatment of the latter with 5‐aminopyrazole derivatives afforded the corresponding pyrazolo[2,3‐a]pyrimidines. 2‐cyano‐N‐[(1,2‐dihydro‐1,5‐dimethyl‐2‐phenyl‐3‐oxo‐3H‐pyrazol‐4‐yl)]acetamide also reacts with heterocyclic diazonium salts to give the corresponding pyrazolo[5,1‐c]‐1,2,4‐triazine derivatives. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:508–514, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20046