Quinoline-like

Quinoline,like pyridine, and the ester give a 1 2 molar labile adduct (117) which is not basic and isomerizes on heating or with acids to a stable isomer (118) as in the pyridine series. It has been... 

Sulfur Heterocyclics. Sulfur containing compounds (thiols, thiophenes, thiazoles,. .. etc.) play a major role in the flavor of raw and processed foods. These compounds have characteristic flavor notes and the flavor thresholds are mostly low. Several reviews (ill, 112, 113) demonstrate the important role of sulfur compounds in food flavors. Organoleptic properties of these compounds may be pleasant, strong nut-like odor of U-methyl-5-vinylthiazole which is present in cocoa (llU) objectionable pyridine-like odor of thiazole (115) quinoline-like odor of benzothia-zole (ll6) strong tomato leaf-like odor of isobutylthiazole (117) and bread crust flavor of acetyl-2-thiazoline (ll8). A mixture of oxazoles, thiazoles, thiazolines, imidazoles, trithiolanes and... 

Quinolines, like pyridines, are susceptible to attack at both the 2- and 4-position however, they are more reactive, quinoline (15 R = H) forming a mixture of 1,2-dihydroquinoline (16 R = H) and 1,2,3,4-tetrahydroquinollne (17 R = H) when reacted in hot ethanol or diglyme. Electron-withdrawing groups... 

Properties Oily liquid quinoline-like odor. Turns red-brown on exposure to light. D 1.086, bp 266C, solidifies at about 0C, soluble in alcohol, ether, and benzene. Slightly soluble in water. 

It was discovered for the first time in a sterilized milk concentrate (Arnold et al., 1966). It has a burnt, phenolic, gassy flavor (Chemisis, 1965). As benzothiazole seems to be met in numerous flavor extracts and as its formation had never been rationalized, Ferretti and Flanagan (1973) were of the opinion that it could be a contaminant from rubber tubing (even with very short connections) and confirmed it with a blank experiment. The authors stated also that benzothiazole could contribute to stale flavor. Maga (1975c) described it as having a quinoline-like, rubbery odor. 

The methano-bridged aza[10]annulene 20 [9], a 10 r-analogue of pyridine, is a stable, yellow compound with a quinoline-like odour and a flattened perimeter (UV Amax 364 nm). The NMR data confirm the aromatic character of 20. The perimeter protons combine the features of a-substituted 1,6-methano[10]annulenes and quinoline (see p 318) the upheld shift of the bridge H-atoms (< ch2 = -0.40 / +0.65) is characteristic. It is caused by the shielding effect of the diatropic heteroarene system. The heteroannulene 20 is less basis (pX = 3.20) than pyridine (pX = 5.23) or quinoline pKa = 4.94). 

An alternative biosynthetic pathway originating from tetrahydrobenzyliso-quinolines like 112 has been proposed to explain the formation of quettamines (113), a new class of isoquinoline alkaloid (67, 71). In laboratory synthesis, the... 

The methano-bridged aza[10]annulene 20 [9], a lOrt-analog of pyridine, is a stable, yellow compound with a quinoline-like odor and a flattened perimeter (UV =... 

The wide variety of ketomethylene and amino ketone monomers that could be synthesized, and the abiUty of the quinoline-forming reaction to generate high molar mass polymers under relatively mild conditions, allow the synthesis of a series of polyquinolines with a wide stmctural variety. Thus polyquinolines with a range of chain stiffness from a semirigid chain to rod-like macromolecules have been synthesized. Polyquinolines are most often prepared by solution polymerization of bis(i9-amino aryl ketone) and bis (ketomethylene) monomers, where R = H or C H, in y -cresol with di-y -cresyl phosphate at 135—140°C for a period of 24—48 h (92). 

Qu tern iy S Its. The ring nitrogen of quinoline reacts with a wide variety of alkylating and acylating agents to produce useful intermediates like A/-benzoylquinolinium chloride [4903-36-0] (8). The quinoline 1,2-adducts, eg, A/-benzyl-2-cyano-l,2-dihydroquinoline [13721 -17-0] (9), or Reissert compounds (28), formed with potassium cyanide can produce 2-carboxyquinoline [93-10-7] (10) or 2-cyanoquinoline [11436-43-7] (11). 

FrielA,nderSynthesis. The methods cited thus far all suffer from the mixtures which usually result with meta-substituted anilines. The use of an ortho-disubstituted benzene for the subsequent constmction of the quinoline avoids the problem. In the FrieWider synthesis (52) a starting material like 2-aminoben2aldehyde reacts with an CX-methyleneketone ia the presence of base. The difficulty of preparing the required anilines is a limitation ia this approach, but 2-nitrocarbonyl compounds and the subsequent reduction of the nitro group present a usehil modification (53). 

Imides (e.g. phthalimide) can be purified by conversion to their potassium salts by reaction in ethanol with ethanolic potassium hydroxide. Hie imides are regenerated when the salts are hydrolysed with dilute acid. Like amides, imides readily crystallise from alcohols and, in some cases (e.g. quinolinic imide), from glacial acetic acid. 

Trachelantamine, according to Syrneva, has a weak atropine-like action and also produces local anaesthesia. Its hydrolytic product, trache-lantamidine, which is structurally identical with tsoretronecanol, yields a p-aminobenzoyl derivative of -which the crystalline hydrochloride, m.p. 230-2°, is said to be as potent a local anaesthetic as cocaine hydrochloride. The chloro- -heliotridane (p. 606) formed by the aetion of thionyl ehloride on trachelantamidine reacts with 6-methoxy-8-aminoquinoline to form 6-methoxy-8-(pseMdoheliotridylamino)-quinoline,... 

In view of the strychnine-like pharmacological action recorded for gelsemine, Janot and Berton have compared the ultra-violet absorption spectra of the two alkaloids, which proved to be remarkably similar. That of sempervirine was quite different and also unlike those of indole, quinoline and cinchonamine, with which it was also compared. 

Just as there are heterocyclic analogs of benzene, there are also many heterocyclic analogs of naphthalene. Among the most common are quinoline, iso-quinoline, indole, and purine. Quinoline, isoquinoline, and purine all contain pyridine-like nitrogens that are part of a double bond and contribute one electron to the aromatic it system. Indole and purine both contain pyrrole-like nitrogens that contribute two - r electrons. 

The chemistry of these polycyclic heterocycles is just what you miglu expect from a knowledge of the simpler heterocycles pyridine and pyrrole Quinoline and isoquinoline both have basic, pyridine-like nitrogen atoms, anc both undergo electrophilic substitutions, although less easily than benzene Reaction occurs on the benzene ring rather than on the pyridine ring, and r mixture of substitution products is obtained. 

Like other carboxylic acids, 2-nit rodibenz[b,/]oxepin-10-carboxylic acid can be decarboxylated in the presence of copper and quinoline to give 2-nitrodibenz[/ ,/]oxepin (2) in 45% yield.101... 

Sometimes lateral chlorination can occur on a methyl or alkylthio substituent, especially when phosphorus pentachloride or its mixtures with phosphoryl chloride are used (91JHC1549). Reactions of 2-methyl-4(I//)-quinoline (67) exemplify this behavior (81CPB1069) (Scheme 31) 2-chloro-3- and -4-methyquinolines are also subject to methyl chlorinations by similar reagents (91JHC1549). Sulfuryl chloride and NCS are also likely to induce a proportion of lateral chlorination (83KFZ1055 86S835). 

The site of dihydroxylation in heterocycles depends on the nature of the heteroaromatic system (Scheme 9.31) usually, electron-rich heterocycles like thiophene are readily biooxidized but give conformationally labile products, vhich may undergo concomitant sulfoxidation [241]. Electron deficient systems are not accepted only pyridone derivatives give corresponding cis-diols [242]. Such a differentiated behavior is also observed for benzo-fused compounds biotransformation of benzo[b] thiophene gives dihydroxylation at the heterocyclic core as major product, while quinoline and other electron-poor systems are oxidized at the homoaromatic core, predominantly [243,244]. 

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