3- coumarin, reaction with

Coumarin, reaction with ArNJ 243 Coupling components... 

Cycloaddition of COj with the dimethyl-substituted methylenecyclopropane 75 proceeds smoothly above 100 °C under pressure, yielding the five-membered ring lactone 76. The regiocheraistry of this reaction is different from that of above-mentioned diphenyl-substituted methylenecyclopropanes 66 and 67[61], This allylic lactone 76 is another source of trimethylenemethane when it is treated with Pd(0) catalyst coordinated by dppe in refluxing toluene to generate 77, and its reaction with aldehydes or ketones affords the 3-methylenetetrahy-drofuran derivative 78 as expected for this intermediate. Also, the lactone 76 reacts with a, /3-unsaturated carbonyl compounds. The reaction of coumarin (79) with 76 to give the chroman-2-one derivative 80 is an example[62]. 

Weak to moderate chemiluminescence has been reported from a large number of other Hquid-phase oxidation reactions (1,128,136). The Hst includes reactions of carbenes with oxygen (137), phenanthrene quinone with oxygen in alkaline ethanol (138), coumarin derivatives with hydrogen peroxide in acetic acid (139), nitriles with alkaline hydrogen peroxide (140), and reactions that produce electron-accepting radicals such as HO in the presence of carbonate ions (141). In the latter, exemplified by the reaction of h on(II) with H2O2 and KHCO, the carbonate radical anion is probably a key intermediate and may account for many observations of weak chemiluminescence in oxidation reactions. 

Reduction. Coumarin is reduced to o-hydroxycinnamyl alcohol by reaction with lithium aluminum hydride (21). By reaction with diborane coumarin gives o-aUylphenol [1745-81 -9] (22). 

Halogenation. Coumarin reacts with bromine under moderate conditions to give 3,4-dibromocoumarin [42974-18-5] (24). The 3-bromocoumarin [939-18-4] and 3,6-dibromocoumarin [58309-97-0] are formed under more drastic conditions (25). 3-Chlorocoumarin [92-45-5] is formed by reaction with chlorine in dichloroethane (26) or without solvent (27). 

Coumarin can also be formed by the reaction of phenol with diketene (40). Similarly, diphenols can react with hydroxycarboxyUc acids or beta-ketoesters to give hydroxycoumaria derivatives. The reaction of resorciaol with malic acid produces umbeUiferone (7-hydroxycoumaria) and its reaction with ethyl acetoacetate gives beta-methylumbeUiferone (7-hydroxy-4-methylcoumaria). 

The conversion of c>-hydroxyaryl ketones la to chromones 2a and/or coumarins 3a with aliphatic acid anhydrides in the presence of the sodium or potassium salt of the corresponding acid and the reaction between lb and aromatic acid anhydrides and the salt of the corresponding acid to form flavones 2b (Allan-Robinson) is called the Kostanecki-Robinson (K-R) reaction. ... 

It is notable that flavone and its derivatives are substituted predominantly in the phenyl group at positions 3 and 4 whereas reaction with Fenton s reagent gives mainly the S-hydroxy isomer." " Similarly, comparison of the distribution of products from coumarin obtained with Udenfriend s system with that given by Fenton s reagent re-... 

The Knoevenagel reaction between o-hydroxyaryl aldehydes and ketones and substituted acetonitriles affords high yields of 3-substituted coumarins in aqueous alkaline media <96H(43)1257>, whilst 4-hydroxycoumarins have been elaborated to pyrano [3,2-c]benzopyran-5-ones by reaction with aromatic aldehydes and malononitiile <96P148>. The imine (10) resulting from the complex reaction of o-hydroxyacetophenone with malononitrile undergoes a 1,5-tautomeric shift in solution <96JCS(P1)1067>. 

It is known that certain coumarins are transformed into 5-(2-hydroxy-phenyl)-3H-pyrazol-3-ones by reaction with hydrazines [10]. Upon appUca-tion of this method, the expected pyrazolones 25 were synthesized starting from 3-nitrocoumarins [11] as known in (Scheme 6). 

The 2,2-dialkylchromenes can easily be obtained from the reaction of coumarin 27 with a Grignard reagent.48 This method has been known for a long time and has not been modified much. The parent chromene 28 has been prepared by reduction and dehydration of 4-chromanone.63 Elimin-... 

In the Diels-Alder reaction with inverse electron demand, the overlap of the LUMO of the 1-oxa-l,3-butadiene with the HOMO of the dienophile is dominant. Since the electron-withdrawing group at the oxabutadiene at the 3-position lowers its LUMO dramatically, the cycloaddition as well as the condensation usually take place at room or slightly elevated temperature. There is actually no restriction for the aldehydes. Thus, aromatic, heteroaromatic, saturated aliphatic and unsaturated aliphatic aldehydes may be used. For example, a-oxocarbocylic esters or 1,2-dike-tones for instance have been employed as ketones. Furthermore, 1,3-dicarbonyl compounds cyclic and acyclic substances such as Meldmm s acid, barbituric acid and derivates, coumarins, any type of cycloalkane-1,3-dione, (1-ketoesters, and 1,3-diones as well as their phosphorus, nitrogen and sulfur analogues, can also be ap-... 

The adipoylated film was washed several times with anhydrous toluene and dioxane, followed by reaction with 7-hydroxycoumarin in dioxane containing sodium hydride for 2 hrs at room temperature. After coupling the coumarin, the film was extracted with methanol in a Soxhlet apparatus, rinsed with water, and dried under vacuum... 

Methylcoumarins bearing hydroxy and other electron-donating groups can be synthesized from the corresponding phenols by reaction with ethyl acetoacetate in the presence of sulfuric acid. Hydrolysis of the ester group in the product then allows the lactone ring of the coumarin to form (Scheme 5.6). 

The Pechmann and Knoevenagel reactions have been widely used to synthesise coumarins and developments in both have been reported. Activated phenols react rapidly with ethyl acetoacetate, propenoic acid and propynoic acid under microwave irradiation using cation-exchange resins as catalyst <99SL608>. Similarly, salicylaldehydes are converted into coumarin-3-carboxylic acids when the reaction with malonic acid is catalysed by the montmorillonite KSF <99JOC1033>. In both cases the use of a solid catalyst has environmentally friendly benefits. Methyl 3-(3-coumarinyl)propenoate 44, prepared from dimethyl glutaconate and salicylaldehyde, is a stable electron deficient diene which reacts with enamines to form benzo[c]coumarins. An inverse electron demand Diels-Alder reaction is followed by elimination of a secondary amine and aromatisation (Scheme 26) <99SL477>. 

Various crown ethers have been constucted onto the 3- and 4- positions of coumarin by way of 3-diazo-2ff-lbenzopyran-2,4(3ff)-dione. Cafbenoid generation under Rh-catalysis is followed by formation of an oxonium ion by reaction with the ether solvent and a sigmatropic rearrangement completes the sequence <99T6577>. 

The 3-position of coumarin is the most susceptible to attack by radicals and reaction with 1,3-diphenyltriazene gives 3-phenylcoumarin (79JHC97). The reaction of sulfuryl... 

A number of natural flavonoids, coumarins and chromones have a prenyl (3-methylbut-2-enyl) side chain which is capable of cyclization on to an oxygen atom to form a pyran ring (77HC(31)633). Prenylation is effected by reaction with either 3-methylbut-2-enyl (prenyl) bromide or 2-methylbut-3-en-2-ol in the presence of a base or a Lewis acid. When this reaction is applied to flavonoids, the prenyl group has a choice of two benzene rings and... 

Both fumaric and maleic acid give rise to coumarins on reaction with phenols. Initially, this route was considered different from the Pechmann reaction, but experimental evidence has been accumulated which suggests that it is simply a variant (73AJC899). Under the acidic conditions, the unsaturated acid could well produce some malic acid, which would then lose carbon monoxide and water as usual. Generally yields in the two approaches to coumarins are much the same. 

The derivatization of DCCH to a carboxylic acid required conversion of the acid to acid chloride using thionyl chloride before reaction with the carbohydrazide group. To evaluate the chemiluminescent characteristics of this coumarin compound, the amide derivative of DCCH was isolated by preparative TLC. Although CL was observed from this product, detection limits were not determined because of the difficulty in quantitative transfer from TLC plates. 

As a general procedure these sensitive fluorescent SAMs are prepared via a three-step procedure. First, a monolayer of N-[3-(trimethoxysilyl)propyl]-ethylenediamine is formed on a glass substrate (Fig. 2) [59]. This layer is converted into the fluorescent SAM by reaction with an amino-reactive fluorescent probe (such as lissamine, dansyl or coumarin) [24], Then the residual amino groups (the steric hindrance renders imposible the reaction of every... 

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