Coumarin reduction

BMI intermediate synthesis [COMPOSITE MATERIALS - POLYTffiR-MATRLO - THERMOSETS] (Vol 7) -coumarin reduction [COUMARIN] (Vol 7)... 

The establishment of equilibria (7), in some cases requires a considerable time. The wave corresponding to coumarin reduction after a time such that the wave shows no further decrease (11) can be utilized to calculate the equilibrium constants Kq and the effect of R1, R2 = alkyl or aryl can be shown (10). The linear dependence found between the half-wave potentials of coumarin and the 6-values indicates that the relative... 

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). 

Coumarin, 4-methyl-7-methoxy-mass spectra, 3, 608 Coumarin, 4-methylsulfonylmethyl-synthesis, 3, 805 Coumarin, nitro-reduction, 3, 691 Coumarin, 3-nitro methylation, 3, 682 Coumarin, 3-phenoxy-synthesis, 3, 807... 

Coumarin-3-carboxylic acid, 6-nitro-ethyl ester reduction, 3, 691 Coumarinic acid synthesis, 3, 685 Coumarinoisocoumarin synthesis, 3, 834 Coumarins acetoxylation, 3, 680 acylation, 3, 689 annelated... 

Asymmetric syntheses of warfarin <96TL8321> and the axially chiral bicoumarin, isokotanin A <96TL3015> have been reported. The former is based on a Rh-catalysed asymmetric hydrogenation of a 3-(a,P-unsaturated ketone) substituted coumarin, whilst the key steps of the latter are an asymmetric Ullmann coupling and a selective demethylation. The stereochemistry of the fused dihydrocoumarin resulting from Li/NHs reduction of... 

The present study reports the anti-inflammatory activity of vanilhn ethers, benzofuranyl coumarins, and unsaturated cyanoesters of 4-aryloxymethyl coumarins 36. When compared with the control all the compounds showed reduction in edema volume. 

Method B involves the preparation of precursor of 2-alkyl-l-benzo-pyrylium salts, as shown in Scheme ll.50 2-Alkylbenzopyrylium salts have been prepared by condensation of salicylaldehyde with appropriate ketone in acetic acid or by alkylation or reduction of coumarin or chromone derivatives. Reaction of 2-alkylbenzopyrylium salts with salicylaldehyde gives directly a spirodibenzopyran or 2-vinynologue benzopyrylium salt 17 which then can be converted into the spirodibenzopyran by piperidine or pyridine. 

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-... 

Harle and Lyons isolated a mixture of dl and meso hydrodimers from the electrochemical reduction of coumarin (146) at pH 6.8 14t Archer and Grim-shaw, on the other hand, isolated a single diastereomer in high yield upon electrolytic reduction of 3-phenylcoumarin (147) in methanolic hydrogen chloride 141), Interpretation of the difference between the behavior of 146 and 147... 

Coumarin (7.88) is a well-known 6-lactone (six-membered ring) of natural origin found in various preparations such as some tobaccos, alcoholic beverages, and cosmetics. Besides reactions of oxidation, reduction, and conjugation, coumarin is also subject to lactone hydration in vivo and in the presence of microsomes [170-174], The resulting metabolites include ortho-coumaric acid (7.89) formed directly from coumarin, 3-(2-hydroxyphenyl)-propionic acid (7.91) formed following reduction of coumarin to dihydrocou-... 

The cathodic reduction of 4-carboethoxy-coumarin in the presence of a catalytic amount of various chiral alkaloids can afford 4-carboethoxydihydrocoumarin in low enantiomeric excess (ee < 20%) (Scheme 140) [253]. In the... 

An asymmetric induction can be performed during the cathodic reduction of various substituted coumarins in the presence of chiral alkaloids. A mixture of dimers and dihydrocoumarins is obtained in various yields according to the nature of the alkaloids (31-89% of dimer and 5-67% of dihydrocoumarin with unsubstituted coumarin) [273]. 

Electroreduction of Coumarin. The principal cathodic reaction of coumarin is the reduction to melilotic acid (Fig. 10.18). A second reduction product is an approximately equimolar mixture of o-hydroxyphenylpropanol and o-propylphenol (Fig. 10.18). Hence, there are three reactions involving coumarin. 

Incorporation of Carbon from Coumarin in Deposits. Incorporation of carbon from coumarin was studied by Rogers and Taylor (36) and Edwards and LeWett (34) using a radiotracer technique with C-labeled coumarin. They found that the consumption of coumarin by incorporation into nickel deposits is small compared with consumption by reduction reaction, by a factor of about 10. 

Vitamin K (phylloquinone) and similar substances with modified side chains are involved in carboxylating glutamate residues of coagulation factors in the liver (see p. 290). The form that acts as a cofactor for carboxylase is derived from the vitamin by enzymatic reduction. Vitamin K antagonists (e. g., coumarin derivatives) inhibit this reduction and consequently carboxylation as well. This fact is used to inhibit blood coagulation in prophylactic treatment against thrombosis. Vitamin K deficiency occurs only rarely, as the vitamin is formed by bacteria of the intestinal flora. 

Coumarin shows a one-electron wave on polarography in aqueous buffers and the half-wave potential is independent of pH [136]. Reduction at a mercury cathode affords the meso- and ( )-isomers of the 4-coupled hydrodimer. Reduction of... 

Reduction of coumarin in aqueous methanol, pH 5-6, in the presence of alkaloids yields an increased amount of dihydrocoumarin. Tliis is also the case for reduction of 4-methylcoumarin and now the 4-methyldihydrocoumarin isolated is optically active [137]. Tlie enantiomeric excess and yield of diliydrocompound both depend on the alkaloid used (Table 3.9) and Low concentrations of alkaloid are effective in achieving asynunetric induction. Concentrations of codeine above 4 mM do not further influence either the yield of dihydrocompound or the degree of induction. 

While this reaction to form coumarin derivatives can be completed in mineral acids, research shows that the reaction was much faster in ILs even at room temperature. The same group used l-butyl-3-methylimidazolium hexafluoro-phosphate IL at high temperatures without employing any acid catalyst. The yields were comparable to chloroaluminate ILs with catalytic amounts of acid at room temperature. They also concluded that Bronsted acidity (produced by HF when [bmimJIPF ] contacts water) was not responsible for the observed activity. Singh et al have used l-butyl-3-methylimidazolium hydrogen sulfate IL in combination with microwave irradiation. They were able to synthesize coumarins in quantitative yields with drastic reduction in reaction times. Soares et al have used [bmim][NbCl6] IL to perform the Pechmann reaction using various phenols with ethyl acetoacetate to produce coumarin in moderate yields (-35%). 

Groups of 26-30 female NMRI mice were fed diets containing 0, 0.05, 0.1 and 0.25% coumarin on days 6-17 of gestation. There was no effect on the total number of implantations or on the proportions that were resorptions or fetal deaths, nor any reduction in fetal weight (Roll Bar, 1967). 

The C=0 stretching frequency of a number of 4-hydroxy- and 4-alkoxy-coumarins, including several anticoagulant drugs, has been identified by isotopic replacement of the carbonyl carbon atom by 3C as the highest frequency band in the 1750-1550 cm-1 region. Introduction of the isotopic atom causes a reduction in the C=0 frequency of ca. 30 cm-1 (82JHC475). 

Many methods have been described for the reduction of coumarins (B-77MI22301) but undesired byproducts are frequently formed. A thorough study of the catalytic reduction of several coumarins has recently shown that careful choice of conditions can lead to high yields of either the 3,4-dihydrocoumarin (306) or the ring opened product (305) which can be cyclized efficiently (Scheme 18) (80JHC1597). 

---