New strategies for the synthesis of heteroannulated 2-pyridinones, substituted 2-quinolinones and coumarins from dehydroamino acid derivatives

Several heteroannulated pyridinones were prepared from the methyl esters of N-Boc-β,β-diheteroaryldehydroalanines by treatment with acetic acid. The latter were obtained by a bis-Suzuki coupling of a β,β-dibromodehydroalanine with heteroarylboronate compounds. The products were obtained in good yields and the cyclization reaction involves the nucleophilic attack of one of the heteroaromatic rings on the carbonyl of the Boc group. The scope of this reaction was extended to the Z-isomer of N-Boc-β-heteroaryldehydrophenylalanines to give 4-phenylpyridinones. A tandem Suzuki coupling-cyclization protocol was developed for the synthesis of 2-quinolinones and coumarins. Thus, β-brominated dehydroamino acids were reacted with 2-(pinacolboronate)aniline or phenol in a one-pot Suzuki coupling followed by lactamization or lactonization to give the corresponding 3-amino-2-quinolinones or 3-aminocoumarins in good to high yields. This type of strategy was also applied to the synthesis of 2-quinolinones and coumarins linked in position-3 to amino acids, using as starting materials brominated dehydropeptides.     

Synthesis and antiproliferative activity of 6,7-aryl/hetaryl coumarins

Two different series of novel analogs of 6,7-aryl/hetaryl coumarins 4a–4h and 8i–8l have been synthesized by using Suzuki–Miyara cross coupling reaction from 4-methyl-2-oxo-2H-chromen-7-yl trifluoro-methanesulfonate and 4-methyl-2-oxo-2H-chromen-6-yl trifluoromethanesulfonate in high yields (70–90%). All synthesized compounds were elucidated by means of IR, ¹H NMR, ¹³C NMR, and MS spectra. The synthesized compounds were tested for antiproliferative activity against different human cancer cell lines (SiHa, MDAMB-231, and PANC-1) and some of products demonstrated the distinctive effect.     

Alkaloids of the flora of Siberia and Altai: XX. Synthesis of 5-aryl(hetaryl)-substituted anthranilic acid esters

Cross-coupling of methyl 2-acetylamino-5-bromobenzoate and 5′-bromolappaconitine with aryl-, furyl-, pyridyl-, and 5-acetylthiophen-2-ylboronic acids or 1-(2-fluoroquinolin-3-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane gave the corresponding 5-aryl(hetaryl)-substituted anthranilic acid derivatives. The use of the two-phase toluene-water system as reaction medium and addition of tetrabutylammonium bromide allows the cross-coupling to be accomplished under mild conditions. The catalytic system Pd(dba)₂-AsPh₃ was found to be efficient in the cross-coupling of methyl 2-acetylamino-5-bromobenzoate with furyl- and pyridylboronic acids, whereas the system Pd(OAc)₂-(o-Tol)₃P ensured good results in the reactions of 5′-bromolappaconitine with hetarylboronic acids. Facile esterification at the C⁸-OH and C⁹-OH groups of the aconitane skeleton was observed in the reactions of 5′-bromolappaconitine and 5′-phenyllappaconitine with phenylboronic acid. 5′-Bromo-8,9-O-(phenylboranediyl)lappaconitine under the Suzuki reaction conditions underwent hydrolysis of the boronic ester moiety with formation of the cross-coupling product of 5′-bromolappaconitine with phenylboronic acid.     

Dehydrogenation of 1-aryl(hetaryl)-1,2,3,4-tetrahydro-9<Emphasis Type="Italic">H</Emphasis>-β-carboline-3-carboxylic acids and their esters with dimethyl sulfoxide

Oxidative dehydrogenation of 1-aryl(hetaryl)-1,2,3,4-tetrahydro-9Н-β-carboline-3-carboxylic acids derivatives with dimethyl sulfoxide leads to the formation of 1-aryl(hetaryl)-9Н-β-carbolines. Simultaneously with the dehydrogenation decarboxylation occurs. At the oxidation with dimethyl sulfoxide of methyl 1-aryl (hetaryl)-1,2,3,4-tetrahydro-9Н-β-carboline-3-carboxylicates methyl 1-aryl(hetaryl)-9Н-β-carboline-3-carboxylates formed whose hydrolysis afforded the corresponding 1-aryl(hetaryl)-9Н-β-carboline-3-carboxylic acids.     

Plant coumarins: XI. Cross coupling reactions with 2-(tosyl)oreoselone

The reaction of a linearly fused furocoumarin, oreoselone, with p-toluenesulfonyl chloride gave 2-tosyloreoselone which showed a high reactivity in palladium-catalyzed cross-coupling reactions with formation of a new carbon-carbon bond. 2-Tosyloreoselone reacted with terminal alkynes in the presence of Pd(PPh₃)₂Cl₂ to give the corresponding 2-alkynylfuro[3,2-g]chromen-3-ones. 2-Aryl(hetaryl)alkynyloreoselones were obtained in high yield directly by palladium-catalyzed reaction of oreoselone with tosyl chloride and aryl(hetaryl)acetylenes. The reaction of 2-tosyloreoselone with aryl(hetaryl)boronic acids in the presence of palladium complexes with uni- and bidentate ligands, tetrabutylammonium bromide, and a base afforded 2-aryl(hetaryl)-substituted oreoselones. 2-Vinyloreoselone was synthesized from 2-tosyloreoselone and potassium trifluoro(vinyl)borate.     

Chemistry of iminofurans: IX. Synthesis and cyclization of (2<Emphasis Type="Italic">Z</Emphasis>)-2-{(2<Emphasis Type="Italic">Z</Emphasis>)-2-[2-(3-R-adamantan-1-yl)-2-oxoethylidene]hydrazinyl}-4-(het)aryl-4-oxobut-2-enoic acids

1-(3-R-adamantan-1-yl)-2-[(triphenyl-λ⁵-phosphanylidene)hydrazinylidene]ethanone reacted with 4-aryl(hetaryl)-2,4-dioxobutanoic acids to give 2-{2-[2-(3-R-adamantan-1-yl)-2-oxoethylidene]hydrazinyl}-4-aryl(hetaryl)-4-oxobut-2-enoic acids which were shown to exist in solution as mixtures of Z- and E-isomeric enehydrazine tautomers. The products underwent cyclization to 3-{[2-(3-R-adamantan-1-yl)-2-oxoethylidene]- hydrazinylidene}-5-aryl(hetaryl)furan-2(3H)-ones.     

Ensembles of rings with a coumarin unit 1. Synthesis of 3-(2-R-thiazol-4-yl)-and 3-(4-R-thiazol-2-yl)coumarins

We have synthesized 3-(2-R-thiazol-4-yl)coumarins (R=H, CH₃, CH₂CN, Ar) by condensation of 3-(-bromoacetyl)coumarins with thioamides. We obtained 3-(4-R-thiazol-2-yl)coumarins (R=H, Ar) by several methods. By reaction of 2-cyanomethyl-4-phenylthiazole with 2-hydroxybenzaldehydes, we synthesized 2-imino-3-(4-phenylthiazol-2-yl)coumarins, which were converted to the corresponding coumarins by acid hydrolysis. For 3-(2-R-thiazol-4-yl)coumarins (R=CH₂CN), we carried out reactions with aromatic aldehydes. We propose alternative methods for synthesis of 2-[2-aryl(hetaryl)-1-cyanoethenyl]-4-(coumarin-3-yl)thiazoles.Ukrainian Pharmaceutical Academy, Kharkov 310002. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1345–1355, October, 1997.     

A new method for the synthesis of 3-aryl-6-(2-pyrrolyl)pyridazines

A new method for the synthesis of 3-halo-6-(N-tosyl-2-pyrrolyl)pyridazine 7 was developed. Suzuki cross-coupling reactions of 7 with arylboronic acids and in situ de-tosylation gave a variety of novel 3-aryl-6-(2-pyrrolyl)pyridazines. It found that protection of the pyrrolyl moiety was necessary for efficient coupling reaction.     

Efficient synthesis of 3-aryl(hetaryl)-1,5,3-dioxazepanes involving catalysts containing Sm and Co

Efficient synthetic procedure was developed for 3-aryl(hetaryl)-1,5,3-dioxazepanes consisting in the transamination of 3-tert-butyl-1,5,3-dioxazepane with arylamines and also by the reaction of 1,2-ethanediol with N,N-bis(methoxymethyl)aryl(hetaryl)amines in the presence of catalytic amounts of Sm and Co compounds.     

Stable nitroxyl radicals with triple bonds: 4-acetylenyl-3-imidazoline-3-oxide-1-oxyls

Cross-coupling reaction of 1-hydroxy-2,2,5,5-tetramethyl-4-[2-(p-iodophenyl)vinyl]-3-imidazoline-3-oxide with copper(I) salts of 1-aryl(hetaryl)alkynes leads to the corresponding 2,2,5,5-tetramethyl-4-[2-(p-aryl(hetaryl)ethynylphenyl)vinyl]-3-imidazoline-3-oxide-1-oxyls in high yields.     

First acetylenic derivatives of stable 3-imidazoline nitroxides

The Stephens-Castro reaction of copper(I) salts of 1-aryl(hetaryl)alkynes with 2,2,5,5-tetramethyl-4-[2-(4-iodophenyl)-vinyl]imidazoline-3-oxide-1-ol proved to be a general method for the preparation of 2,2,5,5-tetramethyl-4-[2-(p-aryl(hetaryl)ethynylphenyl)]vinyl-3-imidazoline-3-oxide-1-oxyles.     

Facile intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins leading to highly fluorescent coumarin-containing polycyclic compounds

The 4-(o-propargyloxy)styrylcoumarins are prepared by the condensation of O-propargylated salicylaldehyde with substituted coumarin-4-acetic acids. The intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins, without any catalyst gives fused-ring coumarins. The reaction in boiling nitrobenzene leads to aromatization of the initial Diels–Alder adduct and these aromatized products are highly fluorescent.     

One-pot assembly of 4-methylene-3-oxa-1-azabicyclo[3.1.0]hexanes from alkyl aryl(hetaryl) ketoximes, acetylene, and aliphatic ketones: a new three-component reaction

A new three-component reaction between alkyl aryl(hetaryl)ketoximes, acetylene, and aliphatic ketones in the superbasic systems KOH/DMSO and LiOH/CsF/DMSO (70-90 °C, initial acetylene pressure 13-15 atm, 5-60 min) affords novel 4-methylene-3-oxa-1-azabicyclo[3.1.0]hexanes in yields of up to 75%. Using KOH/DMSO, the side products of the reaction are O-vinylketoximes and 2-aryl(hetaryl)pyrroles, while with LiOH/CsF/DMSO, the reaction proves to be selective, only minor amounts of the corresponding alkyl aryl(hetaryl) ketones being detectable.     

Stereoselective synthesis of substituted exo-glycals from 1-exo-methylene pyranoses

Halo-exo-glycals of the gluco-, manno- and galacto- series, readily prepared by reaction of 1-exo-methylene pyranoses with iodonium dicollidinium triflate (IDCT), undergo Suzuki or B-alkyl Suzuki cross-coupling reactions with boronic acids or alkyl boranes to yield, in a stereoselective manner, functionalized exo-glycals.     

Unusual Formation of 1,2,4-Oxadiazine Core in Reaction of Amidoximes with Maleic or Fumaric Esters

We have developed a simple and convenient method for the synthesis of 3-aryl- and 3-hetaryl-1,2,4-oxadiazin-5-ones bearing an easily functionalizable (methoxycarbonyl)methyl group at position 6 via the reaction of aryl or hetaryl amidoximes with maleates or fumarates. The conditions for this reaction were optimized. Different products can be synthesized selectively in good yields depending on the base used and the ratio of reactants: substituted (1,2,4-oxadiazin-6-yl)acetic acids, corresponding methyl esters, or hybrid 3-(aryl)-6-((3-(aryl)-1,2,4-oxadiazol-5-yl)methyl)-4H-1,2,4-oxadiazin-5(6H)-ones. The reaction is tolerant to substituents’ electronic and steric effects in amidoximes. As a result, a series of 2-(5-oxo-3-(p-tolyl)-5,6-dihydro-4H-1,2,4-oxadiazin-6-yl)acetic acids, their methyl esters, and 1,2,4-oxadiazoles based on them were prepared and characterized by HRMS, ¹H, and ¹³C NMR spectroscopy. The structures of three of them were elucidated with X-ray diffraction.     

Route selection in the synthesis of C-4 and C-6 substituted thienopyrimidines

Three different routes have been investigated for the preparation of 6-aryl-N-(1-arylethyl)thienopyrimidin-4-amines. First the possibilities of selective Suzuki reactions on 6-bromo-4-chlorothienopyrimidine were investigated. The preference for mono arylation at C-6 could be increased, in the case of Pd(PPh₃)₄ catalysis, by reducing the water content of the reaction, or by using less electron rich Pd-ligands. The highest selectivity was obtained with Pd(OAc)₂ or Pd₂(dba)₃, while reactions with the more electron rich Pd(PPh₃)₄ and especially XPhos gave a lower mono- to dicoupled product ratio. Secondly, two alternative strategies avoiding this selectivity issue were tested. Suzuki reaction on C-6 of 6-bromothienopyrimidin-4(3H)-one (three examples) proceeded in 70-89% yield using Pd(PPh₃)₄ in dioxane/water. Similar conditions on 4-amino-6-bromo-thienopyrimidine (eight examples) gave 67-95% yield. The reaction could be performed with boronic acids containing nonprotected phenolic groups in the ortho, meta and para positions. By prolonging the reaction time, coupling with sterically crowded arylboronic acids was also efficient. Diarylation of 6-bromo-4-chlorothienopyrimidine gave the corresponding 4,6-diarylated derivatives in 71-80% yield depending on the nature of the arylboronic acid.     

Addition of Nitrile Oxides to Allyl Esters of Aryl(hetaryl)carboxylic Acids

3,5-Disubstituted isoxazolines with an aryl(hetaryl)carboxymethyl group in position 5 have been synthesized. The addition reaction of nitrile oxides to allyl esters of aryl(hetaryl) carboxylic acids occurs regiospecifically with the formation of the 5-substituted isomer. Initial pharmacological screening showed that 5-(4-bromobenzoyloxy)methyl-3-(3,4-dimethoxyphenyl)isoxazoline possesses marked nootropic activity.     

Design and synthesis of condensed thienocoumarins by Suzuki–Miyaura reaction/lactonization tandem protocol

A concise and efficient approach to a series of chromen-4-ones with fused thiophene ring has been developed using the Suzuki–Miyaura reaction of bromothiophene-2- and 3-carboxylates with 2-methoxyboronic acids and subsequent cyclization of prepared alkyl (2-methoxy)aryl thiophene-2- and 3-carboxylates under the action of BBr₃/KOtBu. Starting bromothiophenes are easily obtained from corresponding commercially available aminothiophenes by diazotization/bromination reaction.     

Dehydrogenation of 4-aryl(hetaryl) spinacine derivatives with dimethyl sulfoxide

Aromatization of 4-aryl(hetaryl)tetrahydroimidazo[4,5-c]pyridine-6-carboxylic acids and their lithium salts by the action of dimethyl sulfoxide has been revealed for the first time. Heating of these compounds in DMSO for 5–7 h at 90–95°C leads to the formation of 4-aryl(hetaryl)imidazo[4,5-c]pyridine derivatives as a result of dehydrogenation and decarboxylation. Heating of the corresponding lithium salts generated in situ (DMSO, 90–95°C, 3–5 h) affords difficultly accessible 4-aryl(hetaryl)imidazo[4,5-c]pyridine-6-carboxylic acids.     

Chemistry of iminofurans: X. Synthesis and hydrolysis of 5-aryl(hetaryl)-2-[(4,5,6,7-tetrahydro-1-benzothiophen-2-yl)imino]furan-3(2<Emphasis Type="Italic">H</Emphasis>)-ones

5-Aryl(hetaryl)furan-2,3-diones reacted with N-(triphenyl-λ⁵-phosphanylidene)-4,5,6,7-tetrahydro-1-benzothiophen-2-amines to give 5-aryl(hetaryl)-2-[(4,5,6,7-tetrahydro-1-benzothiophen-2-yl)imino]furan-3(2H)-ones whose acid hydrolysis afforded 4-aryl(hetaryl)-2-hydroxy-4-oxo-N-(4,5,6,7-tetrahydro-1-benzothiophen- 2-yl)but-2-enamides.