Synthesis of 3-aryl-3-hydroxypyrrolidin-2-ones and 2-benzyl-9b-hydroxy-3,3a,5,9b-tetrahydro-2H-pyrrolo[3,4-c]quinoline-1,4-dione derivatives from the Baylis-Hillman adducts of isatins

We prepared some 3-aryl-3-hydroxypyrrolidin-2-ones and tricyclic 2-benzyl-9b-hydroxy-3,3a,5,9b-tetrahydro-2H-pyrrolo[3,4-c]quinoline-1,4-diones starting from the Baylis-Hillman adducts of isatin derivatives.     

Reaction of 1-alkyl/aryl-3-amino-1H,3H-quinoline-2,4-diones with urea. Synthetic route to novel 3-(3-acylureido)-2,3-dihydro-1H-indol-2-ones, 4-alkylidene-1′H-spiro[imidazolidine-5,3′-indole]-2,2′-diones, and 3,3a-dihydro-5H-imidazo[4,5-c]quinoline-2,4-diones

1-Substituted 3-alkyl/aryl-3-amino-1H,3H-quinoline-2,4-diones react with urea in boiling acetic acid to give products depending on the type of substitution in position 3 and at the nitrogen atom of the 3-amino group. Starting compounds bearing a primary amino group in position 3 give 3-(3-acylureido)-2,3-dihydro-1H-indol-2-ones. Starting compounds bearing a secondary amino group in position 3 react according to the character of the other substituent in position 3. If there is a hydrogen atom α to the carbon atom C(3), 4-alkylidene-1′H-spiro[imidazolidine-5,3′-indole]-2,2′-diones arise. If a hydrogen atom is not present in this position, the reaction leads to 3,3a-dihydro-5H-imidazo[4,5-c]quinoline-2,4-diones. Reaction mechanisms for these transformations are proposed. All compounds were characterized by their ¹H, ¹³C, IR and atmospheric pressure chemical ionization mass spectra and some of them also by ¹⁵N NMR data.     

Reaction of 3-aminoquinoline-2,4-diones with nitrourea. Synthetic route to novel 3-ureidoquinoline-2,4-diones and imidazo[4,5-c]quinoline-2,4-diones

1-Unsubstituted 3-alkyl/aryl-3-amino-1H,3H-quinoline-2,4-diones react with 1-substituted and 1,1-disubstituted ureas in boiling acetic acid to give 2,6-dihydro-imidazo[1,5-c]quinazoline-3,5-diones. In contrast, the reaction of these amines with nitrourea in dioxane affords novel 3-alkyl/aryl-3-ureido-1H,3H-quinoline-2,4-diones or 9b-hydroxy-3a-alkyl/aryl-3,3a,5,9b-tetrahydro-1H-imidazo[4,5-c]quinoline-2,4-diones, which can smoothly be dehydrated to 3a-alkyl/aryl-3,3a-dihydro-5H-imidazo[4,5-c]quinoline-2,4-diones. All three types of products can be converted to 2,6-dihydro-imidazo[1,5-c]quinazoline-3,5-diones by refluxing in acetic acid.     

Rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones to furo[3,4-c]quinoline-3,4(1H,5H)-diones

Thermally assisted base-catalyzed rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones 1 to the corresponding furo[3,4-c]quinoline-3,4(1H,5H)-diones 2 is reported, and a mechanism of the transformation is proposed.     

Unprecedented reactivity of 3-amino-1H,3H-quinoline-2,4-diones with urea: an efficient synthesis of 2,6-dihydro-imidazo[1,5-c]quinazoline-3,5-diones

Substituted 3-amino-1H,3H-quinoline-2,4-diones react with urea in acetic acid to give novel 2,6-dihydro-imidazo[1,5-c]quinazoline-3,5-diones in high yields. The same compounds were obtained, albeit with small yields, from 3-chloro-1H,3H-quinoline-2,4-diones and urea. In the proposed reaction mechanism, a molecular rearrangement of the primarily formed mono-substituted urea takes place. The prepared 2,6-dihydro-imidazo[1,5-c]quinazoline-3,5-diones were characterized by their ¹H, ¹³C, ¹⁵N NMR and IR spectra and atmospheric pressure chemical ionisation mass spectra.     

Preparation of 2-aminosubstituted 3H-imidazo[4,5-c]quinolin-4(5H)-ones by palladium-assisted internal biaryl coupling reaction

Representatives of the 3H-imidazo[4,5-c]quinolin-4(5H)-ones have shown interesting biological activity. We have found 2-aminosubstituted 3H-imidazo[4,5-c]quinolin-4(5H)-one as a potent dipeptidyl peptidase 4 inhibitor. However effective synthesis of this nucleus with various substituents at the 6-9-positions has not been reported. We report herein the development of a novel and efficient synthesis of 2-aminosubstituted 3H-imidazo[4,5-c]quinolin-4(5H)-ones by palladium-assisted internal biaryl coupling reaction. Our optimization of the reaction conditions revealed that the most important factors for this reaction are use of silver carbonate as a base and high reaction temperature.     

Solid-phase synthesis of 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-thiones and 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-ones

An efficient approach for the synthesis of 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-thiones and 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-ones on solid phase has been developed. The reaction conditions were readily amenable and the products were obtained in good yields and purities after their cleavage from the resin.     

The first entry to pyrrolo[2,3-c]quinoline-2,4(3aH,5H)-diones

Wittig olefination of 3-aminoquinoline-2,4(1H,3H)-diones 1 with ethyl (triphenylphosphoranylidene)acetate (Ph₃PCHCO₂Et) afforded (E)-3-amino-4-ethoxycarbonylmethylene-1,2,3,4-tetrahydro-2-quinolones (E)-2 and pyrrolo[2,3-c]quinoline-2,4(3aH,5H)-diones 3. An alternative approach for the synthesis of 3 via 3-bromoacetamidoquinoline-2,4(1H,3H)-diones 7, their corresponding triphenylphosphonium salts 8, and ylides A that undergo intramolecular Wittig reaction, was investigated. Under the applied reaction conditions, the phosphonium salts 8 and ylides A are so unstable that they partly decompose to 3-acetamidoquinoline-2,4(1H,3H)-diones 9 during the synthesis of 3.     

An efficient synthesis of 4H,5H-pyrano[3,4-c]pyran-4,5-diones from a suitably functionalized 2H-pyran-2-one

An efficient synthesis of ethyl 7-aryl-2-methyl-4H,5H-pyrano[3,4-c]pyran-4,5-dione-1-carboxylate 5, and ethyl 6-aryl-3-cyano-2H-pyran-2-one-4-acetate 6 has been delineated by reaction of suitably functionalized 2H-pyran-2-ones 1 with ethyl acetoacetate 2.     

Aminol initiated Prins cyclization for the synthesis of octahydro-1H-pyrano [3,4-c]pyridine and hexahydro-1H-furo[3,4-c]pyrrole derivatives

Various aldehydes undergo smooth coupling with a branched homoallylic alcohol appended N-tosyl amine (1 & 3) in the presence of 10 mol % BF₃·OEt₂ at room temperature to afford a novel class of 1,8-disubstituted octahydropyrano[3,4-c]pyridine and 1,6-disubstituted hexahydrofuro[3,4-c]pyrrole derivatives in good yields, respectively.     

Synthesis of 2-substituted 3-ethyl-3H-imidazo[4,5-b]pyridines catalyzed by Al-exchanged K10 clay as solid acids

A series of imidazopyridine derivatives have been synthesized efficiently via intramolecular cyclization in excellent yields using Al³⁺-exchanged on K10 montmorillonite clay (Al³⁺-K10 clay) as a reusable heterogeneous catalyst. To the best of our knowledge, this is the first report to utilize Al³⁺-K10 as a catalyst for imidazopyridine synthesis. Many functional groups are tolerated during the synthesis of targeted compounds. The catalyst is reused at least five times with a slight decrease in the yield. This catalyst is environmentally benign, cost-effective, and also provides other advantages such as nontoxicity, operational/experimental simplicity, and mild reaction conditions.     

Regioselective synthesis of 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones and 12H-benzopyrano[3,2-c][1]benzopyran-5-ones by radical cyclization

5-Hydroxy uracils or 4-hydroxy[1]benzopyran-2-ones were refluxed with 2-bromobenzyl bromides in acetone in the presence of anhydrous potassium carbonate to afford a number of 5-(2′-bromobenzyloxy) pyrimidine-2,4-dione (80-92%) or 4-(2′-bromobenzyloxy) benzopyran-7-ones (70-82%) respectively. These were then refluxed with tri-n-butyltin chloride and sodium cyanoborohydride in the presence of a catalytic amount of azobisisobutyronitrile (AIBN) for 3-4 h to give 1H,3H,6H [2]benzopyrano[4,3-d]pyrimidine-2,4-diones (75-85%) or 12H-benzopyrano[3,2-c][1]benzopyran-5-ones (70-85%) respectively.     

Reaction of 3-aminoquinoline-2,4-diones with isothiocyanic acid—an easy pathway to thioxo derivatives of imidazo[1,5-c]quinazolin-5-ones and imidazo[4,5-c]quinolin-4-ones

3-Amino-1H,3H-quinoline-2,4-diones react with thiourea or potassium thiocyanate in boiling acetic acid to give novel 2,3-dihydro-3-thioxoimidazo[1,5-c]quinazolin-5(6H)-ones in high yields. However, if the starting compounds are substituted with a benzyl group at position 3, a C-debenzylation proceeds to give 2,3-dihydro-2-thioxo-1H-imidazo[4,5-c]quinolin-4(5H)-ones. According to a proposed reaction mechanism, a molecular rearrangement of the primarily formed mono-substituted thiourea takes place. All compounds were characterized by ¹H, ¹³C and ¹⁵N NMR and IR spectroscopy as well as by mass spectrometry.     

A novel synthesis of new 2-aryl-6-(arylamino)-1H-imidazo[1,2-b]pyrazole-7-carbonitrile derivatives

New 2-aryl-6-(arylamino)-1H-imidazo[1,2-b]pyrazole-7-carbonitriles are synthesized in good yields, via cyclocondensation of 5-amino-1-(2-oxo-2-arylethyl)-3-(arylamino)-1H-pyrazole-4-carbonitriles, which are prepared by the reaction of 5-amino-3-arylamino-1H-pyrazole-4-carbonitriles and α-bromoacetophenone derivatives in the presence of K₂CO₃ using acetone as the solvent.     

A reaction for the synthesis of benzimidazoles and 1H-imidazo[4,5-b]pyridines via a novel rearrangement of quinoxalinones and their aza-analogues when exposed to 1,2-arylenediamines

An efficient and one-step versatile method for the synthesis of benzimidazoles and 1H-imidazo[4,5-b]pyridines from quinoxalinones and their aza-analogues have been developed on the basis of the novel ring contractions of 3-aroyl-quinoxalinones and their aza-analogues with 1,2-arylenediamines.     

Substituent-induced regioselective synthesis of 1,2-teraryls and pyrano[3,4-c]pyran-4,5-diones from 2H-pyran-2-ones

Substituent-controlled regioselective synthesis of highly functionalized 1,2-teraryls 3a-k has been achieved through ring transformation of 6-aryl-4-(pyrrolidin-1-yl/piperidin-1-yl)-2H-pyran-2-one-3-carbonitriles 1a-g by aryl acetones 2a-c in the presence of powdered KOH in DMF in very good yield. Under similar reaction conditions, 6-aryl-4-methylsulfanyl-2H-pyran-2-ones 5a-f afforded 1,7-diaryl-2-methyl-4H,5H-pyrano[3,4-c]pyran-4,5-diones 6a-j as major products and 3,4-diaryl-2-methyl-6-methylsulfanylbenzonitriles as minor constituents 7a-j.     

An unexpected rearrangement of 3-unsubstituted-2-acyl substituted indole phenylhydrazones. A new method for benz[c]β-carboline synthesis

A new type of rearrangement of 3-unsubstituted-2-acyl substituted indole phenylhydrazones with formation of a quinoline ring under acid catalysed conditions was observed.     

Montmorillonite KSF-catalyzed one-pot synthesis of hexahydro-1H-pyrrolo[3,2-c]quinoline derivatives

Aryl amines react with endocyclic ene-carbamates such as tert-butyl 2,3-dihydro-1H-1-pyrrolecarboxylate and tert-butyl 1,2,3,4-tetrahydro-1-pyridinecarboxylate, on the surface of montmorillonite KSF clay under mild conditions to afford the corresponding 3-aminopropylhexahydropyrrolo[3,2-c]quinoline or 4-aminobutyloctahydrobenzo[h][1,6]naphthyridine derivatives in excellent yields with moderate diastereoselectivity.     

Flash vacuum pyrolysis of 2,2-dioxo-1H,3H-pyrrolo[1,2-c]thiazoles and 2-vinyl-1H-pyrroles

The flash vacuum pyrolysis of new 1,1-dimethyl- and 1-methyl-1H,3H-pyrrolo[1,2-c]thiazole-2,2-dioxides gave penta-substituted 2-vinyl-1H-pyrroles via sigmatropic [1,8]-H shift of the corresponding azafulvenium methide intermediates. In some cases these 1H-pyrroles underwent rearrangement to 2-allyl-1H-pyrroles. Di-substituted 2-vinylpyrroles have also been prepared and their reactivity studied. Under FVP N-benzyl-pyrrol-2-ylpropenoates were converted into 3H-pyrrolizin-3-ones. On the other hand, microwave-assisted reaction of 1-benzyl-2-vinyl-1H-pyrrole gave a 4,5,6,7-tetrahydro-1H-indole derivative.     

Synthesis of imidazolidin-4-one and 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-dione derivatives of primaquine: scope and limitations

The synthesis of imidazolidin-4-one derivatives of primaquine as potential antimalarial agents is described. The target compounds were synthesized in three steps: (i) condensation of (±)-primaquine with N^α-protected amino acids, (ii) removal of the N^α-protecting group, and (iii) reaction of the N-acylprimaquine with a carbonyl compound: acetone, three cyclic ketones and veratraldehyde. Using 2-formylbenzoic acid in the third step afforded 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-diones. All products were isolated in good to excellent yields. Whereas imidazolidin-4-ones were formed as mixtures of all possible diastereomers in equal amounts, 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-diones were produced in a stereoselective fashion. The compounds hydrolyse very slowly (t_1/2 5-30 d) in pH 7.4 buffer to release primaquine. These primaquine derivatives are being submitted to biological assays, and preliminary results of their antimalarial activity are quite encouraging.