An efficient approach to isoindolo[2,1-b][2]benzazepines via intramolecular [4+2] cycloaddition of maleic anhydride to 4-α-furyl-4-N-benzylaminobut-1-enes

Acylation of 4-α-furyl-4-N-benzylaminobut-1-enes with maleic anhydride gave 4-oxo-3-aza-10-oxatricyclo[5.2.1.0^1,5]dec-8-ene-6-carboxylic acid via amide formation followed by intramolecular Diels-Alder reaction of furan (IMDAF). The cycloaddition proceeded under mild reaction conditions (25 °C) and provided only the exo-adduct in quantitative yield. Treatment of this compound with PPA gave isoindolo[2,1-b][2]benzazepine derivatives via ring opening, aromatization and intramolecular electrophilic alkylation. In order to extend the scope of the reaction sequence, 7-oxo-5,11b,12,13-tetrahydro-7H-isoindolo[2,1-b][2]benzazepine-8-carboxylic acids were further transformed into useful synthetic intermediates.     

Synthesis of 6-Acyl-7-aryl-4,7-dihydrotetrazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidine-5-carboxylic acids and their methyl esters

6-Acyl-7-aryl-4,7-dihydrotetrazolo[1,5-a]pyrimidine-5-carboxylic acids and methyl 6-acyl-7-aryl-4,7-dihydrotetrazolo[1,5-a]pyrimidine-5-carboxylates were synthesized by fusion of 4-aryl-2,4-dioxobutanoic acids and their methyl esters, respectively, with 1H-tetrazol-5-amine and aromatic aldehydes. The reaction of methyl 2,4-dioxopentanoate with 1H-tetrazol-5-amine and 2-fluorobenzaldehyde in boiling acetic acid gave methyl 6-acetyl-5-hydroxy-7-(2-fluorophenyl)-4,5,6,7-tetrahydrotetrazolo[1,5-a]pyrimidine-5-carboxylate.     

Cyclocondensation reactions of 5-aminopyrazoles, pyruvic acids and aldehydes. Multicomponent approaches to pyrazolopyridines and related products

The reactions of 3-substituted 5-aminopyrazoles with arylidenepyruvic acids and their synthetic precursors, pyruvic acid and aromatic aldehydes, were studied. Several different reaction pathways for these cyclocondensation reactions were established depending on the reaction conditions and building block selection. The formation of pyrazolo[3,4-b]pyridine-6-carboxylic acids as major products and related compounds was discussed from the mechanistic point of view.     

Multicomponent cyclocondensation reactions of aminoazoles, arylpyruvic acids and aldehydes with controlled chemoselectivity

The multicomponent reactions of 3-amino-1,2,4-triazoles/5-aminotetrazole with phenylpyruvic acids and aromatic aldehydes were studied using conventional thermal heating, ultrasonification and microwave dielectric heating. Two different reaction pathways for these cyclocondensations occurring under either kinetic or thermodynamic control were established depending on the temperature regime and building block selection. In case of aminotriazoles, an unprecedented reaction pathway leading to 5-aryl-7-hydroxy-6-phenyl-4,5,6,7-tetrahydro[1,2,4]triazolo[1,5-a]pyrimidine-7-carboxylic acids was found and discussed.     

Combinatorial synthesis of 4-oxo-4H-imidazo[1,5-a]quinoxalines and 4-oxo-4H-pyrazolo[1,5-a]quinoxalines

A combinatorial synthetic route yielding imidazo[1,5-a]quinoxalines and pyrazolo[1,5-a]quinoxalines is described. The use of 2-fluoroaniline and 1H-imidazole-4-carboxylic acid, respectively, 1H-pyrazole-3-carboxylic acid in the Ugi-reaction (U-4CR) followed by a nucleophilic aromatic substitution (S_NAr) affords the imidazo- as well as the pyrazolo-[1,5-a]quinoxaline moiety in good yield and high diversity.     

Reactivity of sarcosine and 1,3-thiazolidine-4-carboxylic acid towards salicylaldehyde-derived alkynes and allenes

The reaction of sarcosine and 1,3-thiazolidine-4-carboxylic acid with salicylaldehyde-derived alkynes and allenes opened the way to new chromeno[4,3-b]pyrrole and chromeno[2,3-b]pyrrole derivatives. Tetrahydro-chromeno[4,3-b]pyrroles were obtained from the reaction of these secondary amino acids with O-propargylsalicylaldehyde. Interestingly, sarcosine reacted with ethyl 4-(2-formylphenoxy)but-2-ynoate to give a monocyclic pyrrole resulting from rearrangement of the initially formed 1,3-dipolar cycloadduct. Decarboxylative condensation of ethyl 4-(2-formylphenoxy)but-2-ynoate with 1,3-thiazolidine-4-carboxylic acid afforded in a stereoselective fashion the expected chromeno-pyrrolo[1,2-c]thiazole, which structure was unambiguously established by X-ray crystallography. However, the 1H,3H-pyrrolo[1,2-c]thiazole resulting from the opening of the pyran ring was also isolated. The reaction with O-buta-2,3-dienyl salicylaldehyde afforded 3-methylene-hexahydrochromeno[4,3-b]pyrrole. O-Allenyl salicylaldehyde reacted with sarcosine and 1,3-thiazolidine-4-carboxylic acid to give a new type of chromeno-pyrroles. A mechanism proposal for the synthesis of these chromeno[2,3-b]pyrroles has been presented.     

Tandem versus single C-C bond forming reaction under palladium-copper catalysis: regioselective synthesis of α-pyrones fused with thiophene

We herein report a highly convenient protocol for rapid construction of α-pyrone fused with thiophene. This includes one-pot and regioselective synthesis of 4,5-disubstituted and 5-substituted thieno[2,3-c]pyran-7-ones, 6,7-disubstituted and 6-substituted thieno[3,2-c]pyran-4-ones. The synthesis of thieno[2,3-c]pyran-7-ones involves palladium mediated cross coupling of 3-iodothiophene-2-carboxylic acid with terminal alkynes in a simple synthetic operation. The coupling-cyclization reaction was initially studied in the presence of Pd(PPh₃)₂Cl₂ and CuI in a variety of solvents. 5-Substituted 4-alkynylthieno[2,3-c]pyran-7-ones were isolated in good yields when the reaction was performed in DMF. Similarly, 6-substituted 7-alkynylthieno[3,2-c]pyran-4-ones were synthesized via palladium-catalyzed cross coupling of 2-bromothiophene-3-carboxylic acid with terminal alkynes. A tandem C-C bond forming reaction in the presence of palladium catalyst rationalizes the formation of coupled product in this apparently three-component reaction. The cyclization step of this coupling-cyclization-coupling process occurs in a regioselective fashion to furnish products containing six-membered ring only. This sequential C-C bond forming reaction however, can be restricted to the formation of single C-C bond by using 10% Pd/C-Et₃N-CuI-PPh₃ as catalyst system in the cross coupling reaction. 5-Substituted thieno[2,3-c]pyran-7-ones were obtained in good yields when the coupling reaction was performed under this condition. Some of the compounds synthesized were tested in vitro for their anticancer activities.     

Synthesis and biological activity of 1,5-dihydropyridazino-[3,4-b]quinoxalines and a new class of quinolones

A new class of quinolones, 1,4-dihydro-4-oxopyridazino[3,4-b]quinoxaline-3-carboxylic acids and related compounds, were synthesized via oxidation of 1,5-dihydropyridazino[3,4-b]quinoxalines obtained from 2-hydrazinoquinoxaline 4-oxides. Some of the 1,5-dihydropyridazino[3,4-b]quinoxalines, 1,4-dihydro-4-oxopyridazino[3,4-b]quinoxaline-3-carboxylic acids, and related compounds showed biological activity.     

Synthesis of 2-substituted cinchoninic acid amides and their cyclization into 1,2,4-triazolo[4,3-α]-quinoline-9-and 1,2,4-triazino[4,3-a]quinoline-10-carboxylic acid amides

Substituted amides of 2-hydrazino- and 2-ethylhydrazinocinchoninic acids react with pyruvic acid and its ethyl ester to give amides of 3-methyl-4-oxo-1,2,4-triazino[4,3-a]quinoline-10-carboxylic acid. On reaction with aromatic aldehydes they are converted into amides of 2-ethyl-3-phenyl-2,3-dihydro-1,2,4-triazolo[4,3-a]quinoline-9-carboxylic acid, or, in the case of unsubstituted hydrazines, into amides of 2-arylidene-hydrazinocinchoninic acid, which was oxidized to substituted 1,2,4-triazolo[4,3-a]quinolines.Perm Pharmaceutical Academy, Perm 614600. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 701–705, May, 1977.     

Cyclopropanation of N-substituted 3-aryl-2-cyanoprop-2-enamides and derivatives of 5,5-Dimethyl-2-oxo-2,5-dihydrofuran-3-carboxylic acid and 2-oxochromene-3-carboxylic acid with bromine-containing zinc enolates

Zinc enolates derived from 1-aryl-2,2-dibromoalkanones react with N-substituted 3-aryl-2-cyanoprop-2-enamides and 5,5-dimethyl-2-oxo-2,5-dihydrofuran-3-carboxylic and 2-oxochromene-3-carboxylic acid derivatives to give, respectively, N-substituted 2-alkyl-3-aryl-2-aroyl-1-cyanocyclopropane-1-carboxamides, 6-(4-bromobenzoyl)-4,4,6-trimethyl-2-oxo-3-oxabicyclo[3.1.0]hexane-1-carboxylic acid ethyl ester and morpholide, and 1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropla[c]chromene-1a-carboxylic acids as a single geometric isomer. Treatment of 1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxylic acids with carboxylic acid anhydrides leads to the formation of the corresponding 9c-alkyl-1-aryl-3,4-dioxo-9b,9c-dihydro-2,5-dioxacyclopenta[2,3]cyclopropa[1,2-a]naphthalen-1-yl carboxylates.     

Arylidene Pyruvic Acids Motif in the Synthesis of New 2H,5H-Chromeno[4′,3′:4,5]thiopyrano[2,3-d]thiazoles via Tandem Hetero-Diels–Alder-Hemiacetal Reaction

We have developed a tandem hetero-Diels–Alder-hemiacetal reaction using arylidene pyruvic acids with 5-(ortho-hydroxybenzylidene)-substituted 4-thioxo-2-thiazolidinones, leading to 6-hydroxy-2-oxo-5-phenyl-3,5a,6,11b-tetrahydro-2H,5H-chromeno[4′,3′:4,5]thiopyrano[2,3-d][1,3]thiazole-6-carboxylic acids. The stereochemistry of cycloaddition was confirmed by NMR spectra and a single-crystal x-ray diffraction analysis.     

Heterocyclic ketones in the pfitzinger reaction

By the reaction of isatin with heterocyclic ketones (N-tert-butoxycarbonyl derivatives of pyrrolidin-3-one, piperidin-4-one, piperidin-3-one, 1,2,3,4-tetrahydroquinolin-4-one, 8-azabicyclo[3.2.1]octan-3-one, tetrahydropyran-4-one, tetrahydrobenzopyran-4-one) in the presence of KOH (the Pfitzinger reaction) were synthesized quinoline-4-carboxylic acids [4,3]fused with the respective heterocycles. These acids were involved in the reactions with diazomethane and amines at the carboxy group leading to methyl esters and amides, respectively. The esters obtained reacted with hydrazine hydrate affording the acid hydrazides, which entered in the condensation with benzaldehyde to form phenylhydrazones. The esters and amides containing N-tert-butoxycarbonyl fragment lost the tert-butoxycarbonyl group easily to form the secondary amines dihydrochlorides, the [4,3]fused quinoline-4-carboxylic acid derivatives.     

Synthesis and Reactions of 1,6-Dibenzoyl-5H,10H-diimidazo[1,5-a;1',5'-d;]pyrazine-5,10-dione

5,10-Dioxo-5H,10H-diimidazo[1,5-a;1',5'-d]pyrazine-5,10-dicarboxylic acid dichloride in Friedel-Crafts reaction conditions formed with benzene the corresponding 1,6-dibenzoyl derivative 2, which reacted with alcohols and amines to give the keto esters and keto amides of 4(5)-benzoylimidazol-5(4)-carboxylic acids. The reaction of compound 2 with hydrazine gave substituted imidazo[4,5-f]pyridazine, and with o-phenylenediamine gave a derivative of imidazo[4,5-f]-1,4-benzodiazocine - a new heterocyclic system.     

Convenient Synthesis of Some 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles and 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines Bearing 3-Methylthio{7H-1,2,4-triazolo[1,5-d]tetrazol-6-yl}moiety as Possible Antimicrobial Activity

4-Amino-4H-3-methylthio{7H-1,2,4-triazolo[1,5-d]tetrazol-6-yl}-1,2,4-triazole-5thi-ol (1) was condensed with various substituted aromatic aldehydes or acid chlorides to yield a series of arylideneamines 2 or aroylamines 3. These were easily cyclized to the corresponding 6-aryl-3-methylthio7H-1,2,4-triazolo[1,5-d]tetrazol-6-yl-1,2,4-triazolo [3,4-b]-1,3,4-thiadiazoles (4) on treatment with palladium-on-charcoal or phosphorus oxychloride. Compounds 4 were also prepared directly via the reaction of 1 with aromatic carboxylic acids in the presence of phosphorus oxychloride. Cyclocondensation of 1 with a variety of two-carbon cyclizing reagents, namely chloroacetone, pyruvic acid, benzoylformic acid, and benzoin led to the formation of 3-methylthio{7H-1,2,4-triazolo[1,5-d]tetrazol-6-yl}-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines (5?8). Some of the newly synthesized compounds were tested for their antibacterial and antifungal activity against a variety of microorganisms.     

The intramolecular Diels-Alder vinylthiophen (IMDAV) reaction: An easy approach to thieno[2,3-f]isoindole-4-carboxylic acids

The reaction of readily accessible 3-(thien-2-yl)allylamines with maleic anhydride, followed by a domino sequence involving successive acylation/[4+2] cycloaddition steps, leads to the formation of the thieno[2,3-f]isoindole core. The key step, the intramolecular Diels-Alder vinylaren (IMDAV) reaction, proceeds with high level of diastereoselectivity and with formation of a single diastereoisomer of the target product 4,4a,5,6,7,7a-hexahydro-3aH-thieno[2,3-f]isoindole-4-carboxylic acids in excellent yields. If the reaction is carried out at room temperature, it occurs in 2–3 days and the proton migration (H-shift) does not take place at the last stage. In boiling benzene, the reaction is complete after three hours, but in this case a slight impurity of byproducts bearing aromatic thiophene ring – 4a,5,6,7,7a,8-hexahydro-4H-thieno[2,3-f]isoindole-4-carboxylic acids is formed.     

Parallel iterative solution-phase synthesis of 5-amino-1-aryl-[1,2,4]triazolo[1,5-a]pyridine-7-carboxylic acid amide derivatives

The parallel iterative solution-phase synthesis of 5-amino-1-aryl-[1,2,4]triazolo[1,5-a]pyridine-7-carboxylic acid amide derivatives is described. The key intermediate 2,6-bis-aminopyridine-4-carboxylic acid methyl ester was synthesised in a two step procedure in 64% overall yield and elaborated to a variety of triazolopyridine-5-carboxylic acid methyl ester by selective pyridine-N-amination, condensation of the adduct with a wide selection of aldehydes and subsequent cyclisation and oxidation. The desired esters were obtained in yields up to 70%. The final transformation to the amide derivatives was accomplished by application of carefully optimised reaction conditions thus giving access to a library of total 500 triazolopyridine amide derivatives. Iterative synthetic cycles (12-48 library members each) allowing for maximal flexibility in chemistry and maximal efficiency in in vitro biological activity optimisation guided by molecular modelling efforts constitute a synergistic procedure for rapid lead optimisation.     

Studies on pyridonecarboxylic acids . 2. Synthesis and antibacterial activity of 8-substituted-7-fluoro-5-oxo-5H-thiazolo[3,2-a]quinoline-4-carboxylic acids

A series of 8-substituted-7-fluoro-5-oxo-5H-thiazolo[3,2-a]quinoline-4-carboxylic acids was prepared and evaluated for antibacterial activity. These compounds were synthesized from ethyl 2-mercaptoquinoline-3-carboxylates 17 which were obtained from anilines 11 by a route involving an intramolecular cyclization reaction.     

Synthesis of Condensed and Uncondensed Tetrazolo[1,5-<Emphasis Type="Italic">b</Emphasis>][1,2,4]triazines as Potential Antimicrobial Agents

Summary. Reactions of two cyclic amidrazones, the 6-methyl and 6-phenyl derivatives of 7-hydrazinotetrazolo[1,5-b][1,2,4]triazines with mono- and dicarbonyl compounds afforded various heterocyclic systems. Thus, acetic acid, benzoyl chloride, or ethyl chloroformate reacted with the former cyclic amidrazones to yield the corresponding [1,2,4]triazolo[4,3-d]tetrazolo[1,5-b][1,2,4]triazines. With pyruvic acid or ethyl pyruvate the corresponding hydrazone derivatives were obtained, which then cyclized to tetrazolo[1′,5′:2,3][1,2,4]triazino[5,4-c][1,2,4]triazines. The 9,10-dioxotetrazolo-triazinotriazine structures were synthesized by condensative cyclization of the cyclic amidrazones with diethyl oxalate, whereas the reaction of these amidrazones with acetylacetone or ethyl acetoacetate furnished pyrazolyltetrazolo[1,5-b][1,2,4]triazines through the isolable hydrazone intermediates. Some of the representative members of the prepared compounds were screened for antimicrobial activity.     

Iodine-Catalyzed,Multicomponent, One-Pot Synthesis of 5-Aryl-5,8-dihydrotetrazolo[1,5-a]pyrimidine-7-carboxylic Acids

A series of 5-aryl-5,8-dihydrotetrazolo[1,5-a]pyrimidine-7-carboxylic acids (4) were synthesized from 5-aminotetrazole, pyruvic acid, and aromatic aldehydes in one pot in the presence of I₂ with moderate to good yields. Operational simplicity, mild reaction conditions, and ecofriendly procedure make this novel protocol a promising alternative for the fusion of tetrazolopyrimidines. The structures of the products were proved by ¹H and ¹³C NMR spectroscopy, liquid chromatography–mass spectrometry, and elemental analysis.      

Fused v-triazolo-heterocycles. Part 2. Synthesis of 4H-v-triazolo[1,5-d] [1,3,4]oxadiazin-4-ones from the 1-aroylamino-v-triazole-5-carboxylic acids

The synthesis of some 4H-v-triazolo[1,5-d] [1,3,4]oxadiazin-4-ones is described. They are prepared by the reaction of the corresponding 1-aroylamino-v-triazole-5-carboxylic acids with thionyl chloride in the presence of pyridine. The spectroscopic data of these new compounds are also reported.