Direct catalytic asymmetric and anti-selective vinylogous addition of butenolides to chromones

An anti-selective catalytic asymmetric Michael-type vinylogous addition of β,γ-butenolides to chromones was developed. The catalyst system developed herein is characterized by tuning of the steric and electronic effects using a proper Biphep-type chiral ligand to invert the diastereoselection, and improvement of the catalyst turnover by a coordinative phenolic additive. The catalytic protocol renders potentially biologically active natural product analogs accessible in good yield with moderate diastereoselectivity and high enantiomeric purity, mostly greater than 99% ee.

An anti-selective catalytic asymmetric Michael-type vinylogous addition of β,γ-butenolides to chromones was developed.     

Pd-catalyzed atom-economic couplings of triarylbismuth reagents with 2-bromo- and 2,6-dibromochromones and synthesis of medicinally important fisetin

Pd-catalyzed mono- and bis-arylation of chromones was demonstrated using triarylbismuths as threefold aryl transfer atom-economic reagents. This unprecedented study involving functionalized chromones afforded regio-selective mono-arylations leading to functionalized 2-arylchromones in good to high yields. Bis-arylation of 2,6-dibromochromones in one-pot operation furnished 2,6-diarylchromones in moderate to good yields. The present methodology was applied in the synthesis of naturally occurring and medicinally important fisetin molecule in high yield.     

Ruthenium(II)‐Catalyzed Synthesis of Spirobenzofuranones by a Decarbonylative Annulation Reaction

The first decarbonylative insertion of an alkyne through C?H/C?C activation of six‐membered compounds is reported. The Ru‐catalyzed reaction of 3‐hydroxy‐2‐phenyl‐chromones with alkynes works most efficiently in the presence of the ligand PPh₃ to provide spiro‐indenebenzofuranones. Unlike previously reported metal‐catalyzed decarbonylative annulation reactions, in the present decarbonylative annulation reaction, the annulation occurs before extrusion of carbon monoxide.     

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.     

Gas phase reaction between chromones and solvent in an electrospray ionization source

Chromones were measured by using electrospray ionization mass spectrometry in negative mode. Interestingly, in addition to the deprotonated ion ([M ? H]^?), unexpected [M + 17]^? and [M + 31]^? ions were observed in high intensity when water and methanol were used as the solvent. Chromones with different substitutes were tested. Compared with the deprotonated ion, [M + 17]^? and [M + 31]^? ions were observed with higher abundances when the C‐3 site of chromones was substituted by electron withdrawing groups. Based on high performance liquid chromatography‐mass spectrometry (LC‐MS), deuterium‐labeling and collisional‐induced dissociation experiments, a covalent gas‐phase nucleophilic addition reaction between chromone and water, and the formation of a noncovalent complex between chromone and methanol were proposed as the mechanism for the observed [M + 17]^? and [M + 31]^? ions, respectively. Understanding and using these unique gas phase reactions can avoid misannotation when analyzing chromones and their metabolites.     

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.     

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.     

Domino reactions of 1,3-bis-silyl enol ethers with benzopyrylium triflates: efficient synthesis of fluorescent 6H-benzo[c]chromen-6-ones, dibenzo[c,d]chromen-6-ones, and 2,3-dihydro-1H-4,6-dioxachrysen-5-ones

The condensation of 1,3-bis-silyl enol ethers with benzopyrylium triflates, generated in situ by the reaction of chromones with Me3SiOTf, afforded functionalized 2,3-dihydrobenzopyrans; treatment of the latter with NEt3 or BBr3 resulted in a domino retro-Michael-aldol-lactonization reaction and the formation of a variety of 7-hydroxy-6H-benzo[c]chromen-6-ones. The hydroxy group was functionalized by using Suzuki cross-coupling reactions. The methodology reported was applied to the synthesis of the natural product autumnariol and a new fluorescence dye, which exhibits promising optical properties. 2,3-Dihydro-1H-4,6-dioxachrysen-5-ones were prepared by condensation of chromones with 1,3-bis-silyl enol ethers containing a remote chloride group, domino retro-Michael-aldol-lactonization, and an intramolecular Williamson reaction.     

3-(2-二唑啉基)-色酮类化合物的合成研究

报道了取代的邻羟基苯乙酮(1a～1e)经Vilsmeier-Haack反应一步制得3-醛基色酮(2a～2e),2a～2e与取代的芳酰肼(3a～3c)缩合制得15个酰腙类化合物(4a～4o),4a～4o在醋酸酐作用下关环得15个3-(2-苝二唑啉基)-色酮(5a～5o),并通过元素分析,IR,~1H NMR和MS诺数据确证了上述化合物的结构。     

3-(2-卓二唑啉基) - 色酮类化合物的合成研究

报道了取代的邻羟基苯乙酮(1a～1e)经Vilsmeier-Haack反应一步制得3－醛基色酮(2a～2e),2a～2e与取代的芳酰肼(3a～3c)缩合制得15个酰腙类化合物(4a～4o),4a～4o在醋酸酐作用下关环得15个3-(2-卓二唑啉基)-色酮(5a～5o),并通过元素分析,IR,^1^HNMR和MS谱数据确证了上述化合物的结构。     

Synthesis of Bridged Benzazocines and Benzoxocines by a Titanium‐Catalyzed Double‐Reductive Umpolung Strategy

A sequence of two titanium(III)‐catalyzed reductive umpolung reactions is reported that allows the rapid construction of benzazo‐ and benzoxozine building blocks. The first step is a reductive cross‐coupling of quinolones or chromones with Michael acceptors. This reaction proceeds with complete syn‐selectivity for the quinolone functionalization while the anti‐diastereomers are obtained as the major products from chromones. With different reaction conditions, the stereochemical outcome can be altered to afford the syn‐chromanone products as well. A subsequent reductive ketyl radical cyclization forges the tricyclic title compounds in good yields. A stereochemical model explaining the observed stereoselectivities is provided and the product configurations were unambiguously verified by X‐ray analyses and 2D NMR spectroscopic experiments.     

Ultra‐performance convergence chromatography method for the determination of four chromones and quality control of Saposhnikovia divaricata (Turcz.) Schischk.

Ultra‐performance convergence chromatography is an environmentally friendly analytical technique that employs dramatically reduced amounts of organic solvents compared to conventional chromatographic methods. In this study, a rapid, sensitive, and environmentally friendly method based on ultra‐performance convergence chromatography was developed for the quantification of four major chromones present in the roots of Saposhnikovia divaricata (Turcz.) Schischk. Using this method, the analysis time was significantly shortened compared to conventional high‐performance liquid chromatography techniques. In addition, the influence of cosolvent type, cosolvent ratio, column temperature, system pressure, and flow rate on the peak resolution was investigated. The proposed method was validated in terms of its limits of detection, limits of quantitation, linearity, precision, and accuracy. More specifically, the limits of detection of the four chromones ranged from 0.006 to 0.033 μg/mL, while the limits of quantitation ranged from 0.019 to 0.101 μg/mL. Our method also exhibited a good regression (r² > 0.999), excellent precision (RSD < 0.60%), and acceptable recoveries (99.48–102.89%). Finally, the quantities of these four chromones present in 20 commercial samples from Korea and China were successfully evaluated using the developed method, indicating that the proposed method is suitable for the rapid and accurate quality control of Saposhnikovia divaricata.     

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.     

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.     

Analgesic components of saposhnikovia root (Saposhnikovia divaricata)

By activity-oriented separation using the writhing method in mice, the analgesic components of Saposhnikovia root (Saposhnikovia divaricata Schischkin; Umbelliferae) were identified to be chromones, coumarins, polyacetylenes and 1-acylglycerols. Two new components, divaricatol and (3'S)-hydroxydeltoin, were also isolated. The most potent analgesia was observed in chromones such as divaricatol, ledebouriellol and hamaudol, which inhibited writhing inhibition at an oral dose of 1 mg/kg in mice. Acylglycerols also showed inhibition significantly at a dose of 5 mg/kg. In some pharmacological tests using sec-O-glucosylhamaudol, the compound showed analgesia by the tail pressure and the Randall & Selitto methods, and its writhing inhibition was not reversed by naloxone.     

Diversity-oriented synthesis of 3-iodochromones and heteroatom analogues via ICl-induced cyclization

The ICl-induced cyclization of heteroatom-substituted alkynones provides a simple, highly efficient approach to various 3-iodochromones and analogues. This process is run under mild conditions, tolerates various functional groups, and generally provides chromones in good to excellent yields. Subsequent palladium-catalyzed transformations afford a rapid increase in molecular complexity and a convenient preparation of a wide range of functionally substituted chromones, furans, and polycyclic compounds. Iodothiochromenones and iodoquinolinones are also prepared by similar ICl-induced cyclizations.     

Aloe djiboutiensis: Antioxidant Activity,Molecular Networking-Based Approach and In Vivo Toxicity of This Endemic Species in Djibouti

For the first time, the study of the antioxidant activity, the characterization of the phytoconstituants, and the evaluation of in vitro and in vivo toxicity of A. djiboutiensis leave and latex are performed. The antioxidant activity of both latex (ADL) and the methanolic extract of leaves (ADM) is determined using 1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) scavenging radical methods and ferric reducing/antioxidant power (FRAP) assay. The phytochemical study of latex is done using Liquid Chromatography-Mass Spectrometry (LC-MS/MS) and a molecular networking-based approach. The evaluation of in vivo toxicity is performed on mice by oral gavage with a suspension of ADL. Our results show that weak antioxidant activity of ADL and ADM in opposition to their high polyphenol, 83.01 mg and 46.4 mg expressed in gallic acid equivalent (GAE)/g of dry weight (DW), respectively, and flavonoid contents 13.12 mg and 4.25 mg expressed in quercetin equivalent (QE)/g dry weight (DW), respectively. Using the Global Natural Products Social Molecular Networking (GNPS) website, nine (9) anthraquinones derivatives, ten (10) chromones derivatives, two (2) flavonols/ chromones isomers are annotated in the molecular network. The treated mice do not display abnormalities in their general physical appearance and biochemistry parameters, compared to the controls. Only glucose and calcium levels are slightly higher in male treated mice compared to the vehicles.     

含苯并三唑色酮及1,3,4-噁二唑啉类化合物的合成

研究了一种简便的合成2位含氮杂环色酮类化合物的方法。1H-苯并三唑与ClCH~2COOH反应制得1H-苯并三唑-1-乙酸(1),以此为原料合成了一系列2位含1H-苯并三唑-1-甲基色酮(5)和相关的1,3,4-噁二唑衍生物(8)。     

Screening for metal ligands by liquid chromatography--ligand-exchange--electrospray mass spectrometry

Electrospray ionization mass spectrometry is applied for the selective detection of metal ligands after a post-column continuous-flow ligand-exchange reaction. The detection is based on the specific release of a reporter ligand from a metal-reporter ligand complex by a high affinity ligand. Constant infusion and direct-injection experiments are performed to optimize the method. The on-line coupling of a liquid chromatographic separation prior to the continuous flow ligand-exchange reaction enables the screening for high affinity ligands in complex samples. The feasibility of the method is demonstrated by using several ligands with a different affinity for either Cu(II) or Zn(II) ions. The selectivity of the ligand-exchange detection method can be tuned by the choice of the reporter ligand. This is demonstrated by using either 2,2'-bipyridyl or 5-methyl-1,10-phenanthroline as reporter ligands.     

Synthesis of chromones

A general procedure for the preparation of chromones from the boron difluoride complex of o-hydroxyaryl methyl ketones is described. One of the best methods used for the preparation of chromones and benzochromones is the treatment of o-hydroxyaryl methyl ketones with the dimethylacetal of dimethylformamide followed by treatment with sulfuric acid (1). We previously had shown (2) that benzochromone 4 was prepared in reasonable yield by the following reaction sequence.