3-Hydroxy-2-quinolones

Indoles with dibromocarbene are ring-expanded to 3-bromoquinolines (162) and benzofurans behave analogously (Section 3.3.1.7.1). Isatins (163) with CH2N2 form 3-hydroxy-2-quinolones (164). 

According to data from other authors [170], the reaction results in the formation of a mixture of 3-hydroxy-2-quinolone (15%) and 4-hydroxy-2-quinolone (15%). 

With regard to heterocyclic compounds as coupling components, the importance of the formerly widespread pyrazolone-, aminopyrazole-, and 4-hydroxy -quinolone-based yellow azo dyes has greatly diminished with the advent of the tinctorially superior and therefore more economical pyridone azo dyes. Only a few examples have survived and then only for special applications such as for dyeing of acetate fibers. Examples are C.I. Disperse Orange 56 and C.I. Disperse Yellow5. (for structure, see Section 3.2.5). 

Extended Hiickel calculations of the (hydroxy)quinolone 145 (X = NH R = Me) showed that while the tautomer 145a is more stable in the ground state, the tautomer 145b becomes the favored one in the excited state (80IJC(B)989). A similar keto-enol tautomerism was observed in fluorescence emission spectra of (hydroxy)quinolone 146 (98TAL1065). 

The Ni(II) complex of oxine (8-hydroxy quinolone) has higher stabihty constant value of 21.8, as compared to an analogous complex with 2-methyl-8-hydroxy quinolone (17.8)... 

Recently kinetic data have become available for the nitration in sulphuric acid of some of these hydroxy compounds (table 10.3). For 4-hydroxyquinoline and 4-methoxyquinoline the results verify the early conclusions regarding the nature of the substrate being nitrated in sulphuric acid. Plots of log Q against — (Lf + logioflHao) fo " these compounds and for i-methyl-4-quinolone have slopes of i-o, i-o and 0-97 at 25 C respectively, in accord with nitration via the majority species ( 8.2) which is in each case the corresponding cation of the type (iv). At a given acidity the similarity of the observed second-order rate constants for the nitrations of the quinolones and 4-methoxy-quinoline at 25 °C supports the view that similarly constructed cations are involved. Application of the encounter criterion eliminates the possibilities of a... 

Besides AHLs (Table 1), the opportunistic human pathogen Pseudomonas aeruginosa also produces another chemically distinct QS signal molecule, 2-n-heptyl-3-hydroxy-4(lH)-quinolone (PQS 5) [18]. PQS is an integral component of the QS hierarchy and plays an important role in regulating virulence gene expression [19]. 

The cathodic dimerization of 1-hydroxy-3-carbethoxy-2-quinolone occurs at the C-4... 

Procaterol Procaterol, 5-[l-hydroxy-2-[(l-methylethyl)amino]bntyl]-8-hydroxy-2-(l//) quinolone (23.3.25), is synthesized by acylation of 8-hydroxy-2(l//)-qninolone with... 

N-Methyl-4-hydroxy-2-quinolone 183 in a three-component reaction gives spiro pyrano[3,2-c]qionoline-2-ones (02MI2), but indolones 213 with 4-hydroxy-6-methyl-2-pyridone 177 react in a complicated way (97BCJ1625). Ethoxycarbonyl-methylene indolone (Z = COOEt) forms pyrans 224, while dicyano analogs (Z = CN) yield substituted quinoline 225 (Scheme 85). 

The Gould-Jacobs sequence (Scheme 4.1) commences with an addition-elimination reaction between aniline 30 and substituted ethylenemalonate derivative 31 to yield malonic ester 32. Subsequent intramolecular cychzation delivers the 4-hydroxy-3-carboalkoxy-quinolone 33. In the presence of an alkylating agent, 33 is converted to 34. Saponfication of the ester affords quinolone core 35. 

Although hydroxyquinolines in which the hydroxy substituent is present in the benzene ring are known and show phenolic activity, 2- and 4-hydroxyquinoline exist solely as the quinolone tautomers (Box 3.2). 

Anodic cyclization of thiocarboxamides to 1,3-thiazoles is in certain cases a superior method compared to the chemical oxidation as usually performed, using an alkaline solution of potassium hexacyanoferrate(UI). Thus anodic oxidation of 3-anilinothiocarbonyl-4-hydroxycoumarin (110a X = O) and 3-anilinothiocarbonyl-4-hydroxy-2-quinolone (110b) yielded the corresponding 1,3-thiazole derivatives 111a and 111b, respectively. Chemical oxidation... 

An analogous reaction took place with some 6-substituted-2-methyl-4-quinolones and [hydroxy(tosyloxy)iodo]benzene [162] and also between 5-nitro-7-hydroxyquinoline and (diacetoxyiodo)benzene [163]. Depending on the solvent or the presence of alkali, either the iodonium salt or the 1,4-dipole could be isolated. 

The case of i-methyl-4-quinolone is puzzling. The large proportion of the 3-nitro isomer formed in the nitration (table 10.3 cf. 4-hydroxy-quinoline) might be a result of nitration via the free base but this is not substantiated by the acidity dependence of the rate of nitration or by the Arrhenius parameters. From i-methyl-4-quinolone the total yield of nitro-compounds was not high (table 10.3). 

The reduction of 2, either catalytically or with zinc in acetic acid, leads to 3-amino-4-hydroxy-2-quinolone 20 [72TH000], These amino compounds are rather unstable they dimerize with loss of ammonia to "bis-amines", which in turn are readily oxidized to dyes similar to those obtained from ninhydrin and primary amines [68M1205] [68M1543], The amino derivatives 20 are therefore conveniently converted into 0,N-diacetyl derivatives, the N-acetyl derivative 21, or its dehydrated form, the oxazolo derivative 22 [95MI000], The variety of biological activity of oxazolo-quinolines of type 22 has been detected only in recent years [94JHC1647],... 

In the reaction of the isatins 7 [154, 155], 54 [17, 154, 155], or 186 [155, 158, 159] with malonic acid in the presence of sodium acetate [155, 158] or in acetic acid [17, 154, 155, 159] the reaction products were 2-hydroxy-4-quinolinecarboxylic acids, which usually exist in the form of the 2-quinolone derivatives 187, as a result of decarboxylation of the initially formed dicarboxylic acids. Compound 187 with R = R1 = R2 = H and R3 = Me was patented as a plant growth regulator (Aureorysin) [158],... 

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