Coumarins 1a Research Articles

Substituted coumarins as ambident nucleophiles in one-pot hydrogenation/alkylation reaction

The regioselectivity of a one-pot hydrogenation/alkylation reaction of coumarins 1a and 1b with series of alkyl halides has been elucidated as a complementary work to reaction of acylation with the same coumarins. Reaction conditions have provided formation of only C-alkylation products with good to high yield. The results from the experiments are of significant importance to predict reactivity of 3-substituted coumarins in different reaction conditions.

Synthesis and antioxidant study of new polyphenolic hybrid-coumarins

The antioxidant capacity of hydroxylated coumarins and hydroxybenzoic acids has been widely described. However, there is little information on the antioxidant activity when both systems are functionalized. In this work, new hybrid compounds synthesis with a common coumarin scaffold and hydroxybenzoic acids is described. Their antioxidant capacity was evaluated against reactive oxygen species (ROS) using oxygen radical absorbance capacity-fluorescein (ORAC-FL), electron spin resonance (ESR) spin trapping, quenching of superoxide anion, cellular antioxidant activity (CAA) and a ferric reducing ability of plasma (FRAP assay). Additionally, the local reactivity indicator (Fukui index) was calculated to discriminate different reactive sites in the new molecules in which the oxidative process occurs. Likewise, the BDE values were calculated in order to obtain information about the antioxidant capacity for HAT mechanisms. The insertion of organic phenols in a simple coumarin structure produced new derivatives with an improved antioxidant capacity in relation to coumarin 1a. For compound 3c, a synergy phenomenon in ORAC-FL and the FRAP test was observed. For compound 3b, this phenomenon was observed in the superoxide scavenging test. According to the CAA assay results, the activity of the new compounds is limited to those oxidative processes in lipophilic media (e.g., bio membranes).

An Efficient Microwave‐Assisted Synthesis and Antimicrobial Activity of Novel 2‐Amino 3‐Cyano Pyridine Derivatives using Two Reusable Solid Acids as Catalysts

Two solid acids, Fe3+ K‐10 montmorillonite clay and HY‐zeolite, have been employed efficiently for synthesis of 2‐amino 3‐cyano pyridines 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l, 4m, 4n, 4o, 4p, 4q, 4r, 4s, 4t, 4u, 4v, 4w, 4x by multicomponent reaction of 3‐acetyl 4‐hydroxy coumarin 1a, 1b, 1c, 1,3‐diphenyl‐1H‐pyrazole‐4‐carbaldehyde 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, malononitrile 3, and ammonium acetate. Both the catalysts are recoverable and recyclable. The main significant of this procedure is short reaction time, high yields, easy workup procedure, and being environmentally friendly. The structures of all the compounds have been well characterized by IR, 1H NMR, 13C NMR, and mass spectral data. All the synthesized compounds were screened for their antimicrobial and antifungal activities.

Microwave assisted synthesis and biological activity of 3-aryl-furo[3,2-c]coumarins

The synthesis of various 3-aryl-furo[3,2-c]coumarins 4a–l has been carried out by employing two different methodologies under microwave irradiation condition. In the first method different 3-aryl-furo[3,2-c]coumarins 4a–l have been synthesized by reacting various 4-hydroxy coumarins 1a–d with appropriate 2-aryl-1-nitro ethenes 2a–c under Nef reaction condition, while in the second method the same target compounds have been synthesized by reacting various 4-hydroxy coumarins 1a–d with appropriate aroylmethyl bromides 3a–c under Feist–Benary reaction condition. All the synthesized compounds were characterized by elemental analysis and IR, 1H NMR, 13C NMR, DEPT-90 spectral analysis. All the synthesized compounds 4a–l were screened for their antimicrobial activity.

Synthesis of 3-Benzylcoumarins Using Suzuki Coupling Reaction

Coumarins are a structural scaffold in the numerous natural product 1 and one of well known oxygen containing heterocycles showing a variety of biological activities. 2 In addition, they have found in the technological applications 3 and used as intermediate for the synthesis of important molecules. 4 Because of their diverse applications, a variety of classical routes 5 to coumarins such as Pechmann, Knoevenagel, Perkin, Reformatsky and Wittig condensation reactions have been reported. However, these methods have their own problems such as harsh reaction conditions, multistep synthesis or low chemical yield. To overcome the problems associated with these classical methods, many strategies for the convenient and versatile synthesis of coumarin derivatives by direct ring formations 6 and by metal catalyzed coupling reactions of coumarin derivatives 7,8 have recently been developed. Among coumarin derivatives, 3-alkylcoumarins including benzylcoumarins are important building block and showed important biological activities. 9 As an example, Warfarin, a 3benzylcoumarin derivative, is the most widely used oral anticoagulant. 10 New, convenient, and versatile syntheses of 3-alkylcoumarins has been developed. 9 Wadia et al. reported the synthesis of 3-benzylcoumarins from the reaction of a complex of the amides and POCl3 with substituted salicylaldehydes. 9 Brase and his colleagues synthesized successfully the 3-benzylcoumarins from the salicylaldehydes and cinnamyl aldehydes using nucleophilic carbenes in ionic liquid in one-step. 9 Recently, 3-allylcoumarin was prepared by decarboxylative allylation of allyl ester of 3-carboxylcoumarin using palladium catalyst under mild condition. 9 But those methods have several drawbacks such as limited number of substrates, and harsh reaction condition. Palladium catalyzed cross coupling reactions have emerged as a powerful method for the carbon-carbon bond formation. Among them, Suzuki coupling is the most widely used method, because organoboronic acids are generally non-toxic and thermally, air-, and moisture-stable. The palladium catalyzed benzyl halides and allyl halide coupling with organoboronic acids are also well established 11 and the reaction has been known to proceed through η 3 -complex. 12 Here, we report the efficient cross coupling reaction of 3-(chloromethyl)coumarins prepared from salicylaldehydes 13 with arylboronic acid to give the corresponding 3-benzylcoumarins in excellent yields (Scheme 1). The reaction of 3-(chloromethyl)coumarin 1a and phenylboronic acid as a model was first examined using palladium acetate and Na2CO3 as a base in methanol.

Synthesis and antimicrobial activity of some 7‐aryl‐5,6‐dihydro‐14‐aza[1]benzopyrano[3,4‐b]phenanthren‐8H‐ones

AbstractThe title compounds, 7‐aryl‐5,6‐dihydro‐14‐aza[1]benzopyrano[3,4‐b]phenanthren‐8H‐ones 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, 3l have been synthesized by reacting various 4‐hydroxy coumarins 1a, 1b, 1c with 2‐arylidene‐1‐tetralones 2a, 2b, 2c, 2d in the presence of ammonium acetate and acetic acid under Krohnke's reaction condition. The structures of all the synthesized compounds were supported by analytical, IR, 1H‐NMR, and 13C‐NMR data. All the synthesized compounds 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, 3l have been screened for their antibacterial activities against Escherichia coli (Gram −ve bacteria), Bacillus subtilis (Gram +ve bacteria), and antifungal activity against Candida albicans (Fungi). J. Heterocyclic Chem., (2011).

ChemInform Abstract: Synthesis and Reactions of Phosphino- and Phosphono-Substituted Coumarins.

Abstract Aminophosphine-ylides 4a and 4b were prepared in high yields by treating 3-acetyl coumarins 1a and 1b with trisdimethylaminophosphine 2 . Chemical degradation reactions for the ylides 4a , b (e.g., formation of the phosphonium salt, Wittig reaction, hydrolysis) were suggested and illustrated. Reaction of trialkyl phosphites with 3-acetyl coumarins 1a and 1b yields the respective dialkyl phosphonates (1:4 addition) 12a , b . Conversely, dialkyl phosphonates react with the same species 1a , b to give the tautomeric monophosphonates 17A 17B via both 1,4- and 1,2 additions, in contrast to earlier reports.

Efficient syntheses of 6-prenylcoumarins and linear pyranocoumarins: Total synthesis of suberosin, toddaculin, O-methylapigravin (O-methylbrosiperin), O-methylbalsamiferone, dihydroxanthyletin, xanthyletin and luvangetin

Synthesis of naturally occurring 6-prenylcoumarins (1a, 2c and 3a) and their derivatives 1c, 1d, 1e, 2d and 3b–d starting from 2-prenyloxybenzaldehydes (8, 12 and 14) using tandem Claisen rearrangement and Wittig reaction is described. The coumarins 1a, 1e and 2c are converted to dihydropyranocoumarins (5a–e). The conversion of dihydroxanthyletin 5a and dihydroluvangetin 5d to the naturally occurring linear pyranocoumarins xanthyletin 6a and luvangetin 6b is also described.

Synthesis and reactions of phosphino- and phosphono substituted-coumarins

Aminophosphine-ylides 4a and 4b were prepared in high yields by treating 3-acetyl coumarins 1a and 1b with trisdimethylaminophosphine 2. Chemical degradation reactions for the ylides 4a, b (e.g., formation of the phosphonium salt, Wittig reaction, hydrolysis) were suggested and illustrated. Reaction of trialkyl phosphites with 3-acetyl coumarins 1a and 1b yields the respective dialkyl phosphonates (1:4 addition) 12a, b. Conversely, dialkyl phosphonates react with the same species 1a, b to give the tautomeric monophosphonates 17A 17B via both 1,4- and 1,2 additions, in contrast to earlier reports.

Uncoupling Behavior of the 4-Phenylcoumarins in Spinach Chloroplasts: Structure−Activity Relationships

4-Phenylcoumarins isolated from Exostema caribaeum and Hintonia latiflora (Rubiaceae) and some semisynthetic derivatives acted as uncouplers in spinach chloroplasts. The glycoside 5-O-β-d-glucopyranosyl-7-methoxy-3‘,4‘-dihydroxy-4-phenylcoumarin (3), 5,7,3‘,4‘-tetrahydroxy-4-phenylcoumarin (1a), and 7-methoxy-5,3‘,4‘-trihydroxy-4-phenylcoumarin (2a) inhibited ATP synthesis and proton uptake. On the other hand, basal and phosphorylating electron transport were enhanced by these compounds. The light-activated Mg2+-ATPase was slightly stimulated by coumarins 1a and 2a. In addition, at alkaline pH compound 1a stimulated the basal electron flow from water to methylviologen, but at the pH range from 6.0 to 7.5 the coumarin did not have any enhancing effect. Compound 1a, which possesses four free phenolic hydroxyl groups, was the most active uncoupler agent. Methylation (2b, 4), acetylation (2a), or glycosylation (1−3) of the phenolic groups at C-3‘, C-4‘, and C-5 resulted in a reduction or loss of the uncoupling activity. Therefore, the phenolate anions may be the active form responsible for the uncoupling behavior of 4-phenylcoumarins. Keywords: Exostema caribaeum; Hintonia latiflora; Rubiaceae; phenylcoumarin; photosynthesis; uncouplers

Chemical Transformations of Some Coumarin‐Enaminoester Adducts

AbstractThe adducts 4a, b, initially formed from the coumarins 1a, b and ene‐diamino ester 2, have been converted into substituted benzopyrano[3,4‐c]pyridines 5, 7, and 8. The tricyclic compound 7 is obtained by base‐catalyzed rearrangement of the decarboxylated adduct 3. The possible intermediate of this reaction is trapped as an acetate 6 upon treatment of 3 with acetic anhydride. The adduct 10 (from the acid 1a and ethyl 3‐aminocrotonate) decarboxylates spontaneously to give the dihydrocoumarin 11 which rearranges further to yield the 2‐pyridinone 12. The cyclohexenone 13 is isolated as byproduct.