Palladium-catalyzed cascade reactions of coumarins with alkynes: synthesis of highly substituted cyclopentadiene fused chromones

The coupling of coumarins with alkynes is described, which proceeds through a palladium-catalyzed cascade sequence. This process provides a new route to the synthesis of highly substituted cyclopentadiene fused chromones.     

Synthesis of 2-substituted chromones,chromanones, and their thio analogues using organocopper reagents

Improved use of organocopper reagents provides a general route to unsymmetrical 2,2-dialkylchomanones and thiochromanones from chromones and thiochromones via a simple addition - oxidation - addition sequence     

Palladium catalyzed three component coupling reaction between chromones, alcohols, and allylic acetates: diversity-oriented synthesis of highly substituted chromones

This paper describes the palladium catalyzed highly efficient three component coupling (TCC) reactions between chromones, allylic acetates, and alcohols, which lead to a library of multiply substituted chromones. The activity of various palladium catalysts, such as Pd(PPh₃)₄ and Pd₂dba₃·CHCl₃ and their combination with various bisphosphine ligands, was investigated by using THF as a solvent, which revealed that Pd(PPh₃)₄ catalyst was the best one. The reaction most probably proceeds via the formation of benzopyrilium cation, generated from the reaction between chromones and allyl acetate, in the presence of palladium catalyst. The subsequent trapping of the benzopyrilium cation by alcohols would give the corresponding products in excellent yields. This alkoxy-allylation reaction was highly diastereoselective and only one diastereomer was obtained in all the cases.     

Palladium(II)-catalyzed direct intermolecular alkenylation of chromones

A new efficient method for the direct alkenylation of chromones via a palladium(II)-catalyzed C-H functionalization reaction was developed. The use of pivalic acid with Cu(OAc)(3)/Ag(2)CO(3) provided superior reactivity in the cross-coupling of chromones with alkene partners. This approach represents a significant advance over the existing two-step method and afforded various 3-vinylchromone derivatives, which are privileged structures in many biologically active compounds and versatile synthetic building blocks.     

A facile route to isoflavone quinones via the direct cross-coupling of chromones and quinones

A straightforward and efficient method for the palladium-catalyzed direct cross-coupling of chromones with various quinones has been developed to rapidly construct isoflavone quinone structural motifs.     

Synthesis of functionalized chromones via organocatalysis

A facile and versatile organocatalytic approach to access 2-substituted and 2,3-disubstituted chromone derivatives under mild conditions was developed, which was effectively catalyzed by novel proline phenylsulphonylhydrazide or pyrrolidine. As a result, diversely functionalized chromones were obtained in up to 99% yield. In addition, further modification of the corresponding chromones afforded novel polycyclic chromones.     

Synthesis of 2-(4-Quinolyl) and 2-(3-Quinolyl) Chromone Derivatives

In continuing search of the structure-activity relationship of heterocyclic chromones, 4-quinolyl and 3-quinolyl moieties were each introduced to the C-2 position of chromones. A total of 12 quinolyl chromones were synthesized. 4-Quinolinecarboxaldehyde was condensed with 2-hydroxyacetophenones to provide the chalcones. These intermediates were then subjected to selenium dioxide dehydrogenation to yield the 6 new 4-quinolyl chromones. 3-Quinolinecarboxaldehyde was condensed with 2-hydroxyacetophenones in the presence of dilute alkali to give aldol compounds of chalcones (dehydration products of aldols). Ring cyclization of the chalcones yielded the other 6 new 3-quinolyl chromones.     

Expedient synthesis of xanthones and multi-functionalized chromones from 1,1-diacyl cyclopropanes

We report the rapid synthesis of various cycloheptane-fused chromones and an oxepine fused flavone in 5 steps from the corresponding 2-hydroxy acetophenone. Furthermore, we describe the synthesis of xanthones, in moderate to good yield, from 2,3-disubstituted flavones using a Friedel Crafts alkylation strategy.     

Epoxidation of homoisoflavones

A comparative study of the epoxidation of homoisoflavones (3‐benzyl‐4‐chromones) 1–4 has been performed by various oxidizing agents, víz. Epoxidation with isolated dimethyldioxirane (Method A), with alkaline hydrogen peroxide (Method B), and with sodium hypochlorite (Method C) to obtain the epoxides 4–8 . Compounds 2 and 3 have also been oxidized with a combination of dimethyldioxirane and Jacobsen's Mn(III)salen catalysts (R,R)‐11 and (S,S)‐ 11 to afford 3‐benzoyl‐4‐chromones 9 and 10 . Structures of all new compounds have been elucidated by microanalyses, ir and nmr spectroscopic measurements.     

Electrophilic carbon transfer in gold catalysis: synthesis of substituted chromones

Using easily accessible aromatic alkoxy-arylalkynones, we have investigated the gold-catalyzed intramolecular addition of ethers to alkynes, to give easy access to various substituted chromones. This reaction involves the transfer of the ether substituent via a carbodemetallation process. We also noticed a competing isomerization of several starting materials for which we propose a second gold catalyzed mechanism.     

Lewis Acid-triggered selective zincation of chromones, quinolones, and thiochromones: application to the preparation of natural flavones and isoflavones

A Lewis acid-triggered zincation allows the regioselective metalation of various chromones and quinolones. In the absence of MgCl(2), a C(3) zincation is observed, whereas in the presence of MgCl(2) or a related Lewis acid, C(2) zincation occurs. Applications to a natural flavone, isoflavone, and quinolone are shown.     

Applications of Baylis-Hillman adducts: a simple, convenient, and one-pot synthesis of 3-benzoylquinolines

A simple and convenient synthesis of 3-(2-hydroxybenzoyl)quinoline derivatives via the treatment of 3-[hydroxy(2-nitroaryl)methyl]-4H-chromen-4-ones, derived from chromones and various 2-nitrobenzaldehydes, with Fe/AcOH, in a one-pot operation, is described.     

Synthesis of 2‐Dihydrooxadiazolinyl Chromones

Reactions of the substituted 2‐formyl chromones with aroylhydrazines gave corresponding 2‐(aroylhydrazonomethylidyne) chromones. Then 2‐(3′‐acetyl‐5′‐aryl‐2′,3′‐dihydro‐1′,3′,4′‐oxadiazol‐2′‐yl) chromones were prepared by these 2‐(aroylhydrazonomethylidyne) chromones under refluxing with Ac₂O. All target compounds were characterized through elemental analysis and IR, ¹H NMR, MS.     

A very simple solvent-free method for the synthesis of 2-arylchromones using KHSO4 as a recyclable catalyst

An efficient and solvent-free procedure for the synthesis of flavones using KHSO₄ as a recyclable catalyst is described. The methodology represents an environmentally friendly process in comprehensive consideration compared with other catalytic systems listed in publications. This method provides a clean, simple, solvent-free reaction and useful alternatives to prepare flavones and chromones. The use of KHSO₄ catalyst provides excellent yields, also leading to an easy separation and recovery of the catalysts, which allows both low environmental impact and low cost. Other green advantages of the method are the low formation of wastes and the replacement of corrosive, soluble mineral acids.     

Base-Promoted Difunctionalization of Alkynes: One-Pot Synthesis of Polysubstituted Chromones

A transition-metal-free one-pot procedure for the difunctionalization of alkynes by C−C triple bond oxidation and transformation towards chromone derivatives has been developed. It involves cascade reactions for carbonylation of alkynes, base-promoted C−C σ-bond cleavage, and intramolecular cyclization. This procedure provides an efficient protocol for the synthesis of polysubstituted chromones from readily available starting materials.     

SYNTHESIS OF α-AZIDO-2′-HYDROXYCHALCONES FROM CHALCONE DIBROMIDES WITH AZIDE ION

ABSTRACT

The reaction of the 2′-hydroxychalcone dibromides with azide ion was found to afford various products such as α-azido-2′-hydroxychalcones, flavones, aurones, isoxazoles or the parent chalcones depending on the substituent pattern of the substrate. Efficient transformation of α-azido-2′-hydroxychalcones to 3-amino-2-substituted chromones was also demonstrated.     

Chemistry of the hetero analogs of isoflavones. 22. Mannich reaction in the benzimidazole and benzothiazole analogs of isoflavones

New 3-(2-benzothiazolyl)chromones were obtained by the reaction of 2-(2,4-dihydroxy-5-ethylphenacyl)-benzothiazole with triethyl orthoformate or carboxylic acid anhydrides. Aminomethylation of the chromones and also of familiar 3-(2-benzimidazolyl)chromones by substituted 1,1-diaminomethanes gave Mannich bases.For Communication 21, see [1].Taras Shevchenko Kiev University, Kiev, Ukraine. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1072–1078, August, 1998.     

Reactions of 3-(polyfluoroacyl)chromones with hydroxylamine. The first synthesis of 3-cyano-2-(polyfluoroalkyl)chromones

Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine proceeds via nucleophilic 1,4-addition followed by opening of the pyrone ring and subsequent cyclization to 4-(polyfluoroalkyl)-4H-chromeno[3,4-d]isoxazol-4-ols in good yields. On treatment with trifluoroacetic acid, the isoxazole ring of this annulated heterocyclic system opens to give 3-cyano-2-(polyfluoroalkyl)chromones. Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine hydrochloride occurs only at the carbonyl carbon atom connected to the R^F group to give the corresponding oximes in low yields.     

Hypervalent Iodine‐Mediated Selective Oxidative Functionalization of (Thio)chromones with Alkanes

C?C bond formation is the most fundamental way for the chain propagation in organic molecules. This achievement through tandem oxidation of two different C?H bonds represents the state of the art in organic synthesis. Selective functionalization of the ubiquitous aliphatic C?H bonds offers an attractive option for this oxidative cross‐coupling methodology. To develop such a methodology under mild and “metal‐free” conditions remains challenging. Herein, we report hypervalent iodine‐mediated selective oxidative functionalization of aliphatic C?H bonds of alkanes with chromones and (thio)chromones. A wide range of alkanes, both cyclic and acyclic, has been found to react selectively and predictably in good yields. The developed methodology is also the first report of a direct oxidative functionalization of the C‐2 position of (thio)chromones with alkanes to access bioactive compounds.     

Synthesis and biological activity of chromones annelated at the C(7)–C(8) bond with heterocycles (review)

Published data on the synthesis of chromones annelated at the C(7)–C(8) bond with nitrogen-, oxygen-, and sulfur-containing heterocycles of various sizes, including those with two and three heteroatoms, are discussed. Data on the biological activity of chromone derivatives isolated from natural sources and obtained synthetically are presented.