Quinoline-8-thiol

Quinoline 2-thiols are excellent precursors for construction of this ring system. Thus, allylation or vinylation of quinoline thiol 640 gave 2-vinylthioquinolines 641 or 2-allylthioquinolines 642 which were... 

Nitrogen nucleophiles used to diplace the 3 -acetoxy group include substituted pyridines, quinolines, pyrimidines, triazoles, pyrazoles, azide, and even aniline and methylaniline if the pH is controlled at 7.5. Sulfur nucleophiles include aLkylthiols, thiosulfate, thio and dithio acids, carbamates and carbonates, thioureas, thioamides, and most importandy, from a biological viewpoint, heterocycHc thiols. The yields of the displacement reactions vary widely. Two general approaches for improving 3 -acetoxy displacement have been reported. One approach involves initial, or in situ conversion of the acetoxy moiety to a more facile leaving group. The other approach utilizes Lewis or Brmnsted acid activation (87). 

Examples from preparative chemistry indicate the possible occurrence of special alpha-e ects in several other cases. The different reaction of 2- and 4-ethoxy quinolines with a thiol yielding carbostyril and a 4-arylthio derivative, respectively, may indicate the intervention of structures such as 17 in the transition state of the 2-isomer. 

Treatment of quinoline 2-thiol derivative 660 with 2,3-dibromopropanol gave the thiazoloquinoline 661 which upon treatment with K2CO3 gave a mixture of 662 and the rearrangement product 663. Separation, hydrolysis and reaction of 662 with A -methylpiperazine afforded 664 (93JMC3148)... 

Anodic inhibitors limit the oxidation of iron by sharing the lone pair electrons on the nitrogen with a metal ion or atom and supressing the anodic reaction. Examples are benzotriazole (at high concentrations), pyridines, thiols, and quinolines. 

The S-methyldithiocarbazates of both 2-formylquinoline, 18, and 1-formyliso-quinoline, 19, yield diamagnetic green [FeL2] complexes from iron(II) sulfate [131]. Coordination for both complexes is via the ring nitrogen, azomethine nitrogen and thiol sulfur based on infrared studies. 

The S-methyldithiocarbazates of both 2-formylquinoline, 18, and 1-formyliso-quinoline, 19, when mixed with cobalt(II) salts in ethanol-dimethoxypropane, yield [Co(L-H)2]N03 and [Co(L-H)2]2[CoA4], where A = Cl, Br, I, NCS, or NCSe [145]. Magnetic and spectral data support these stoichiometries and bonding is via the ring nitrogen, azomethine nitrogen, and thiol sulfur. More recently [146], [Co(19-H)2]2[CoCl4] has been shown to have d-d bands consistent with the presence of both cobalt centers. 

Thiol-thione tautomerism is similar to that exhibited by the oxygen analogues but with the a- and y-thiones, e.g. (129), slightly more favoured than the corresponding a- and y-oxo compounds. UV and other data have indicated the predominance of the thione forms of quinoline-2- and -4-thione, e.g. (130), isoquinoline-1- and -3-thione, e.g. (131), and acridine-9-thione (132) (76AHC(S1)144>. 

UV and pKa measurements show that pyridine-3-thiol and quinoline-3-thiol occur predominantly in the zwitterion form, e.g. (133) (76AHC(S1)144). Quinolines carrying a mercapto group on the benzo ring exist in the zwitterion or the zwitterion extended quinone form to a larger extent than do the analogous hydroxy compounds (63AHC(S1)400). 

A preparation of quinoline-3-thiol from the diazonium salt, according to prior literature, and using potassium ethyl xanthate, abnormally threw down a solid during extraction of the product into ether. This solid, filtered and dried, exploded on prodding with a metal spatula. The solid had an nmr spectrum consistent with the expected product, an 5-aryl-O-ethyl xanthate. Although the author appears aware of only the arenediazosulfide hazard, this must have been the 5 -arenediazoxanthate. A misprint renders quinoline as quinine. 

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... 

Disodium salt of 3,3 -thiodiquinoline-4-thiol when reacted with diiodomethane gives the corresponding 1,3,6-trithiocine ring system with two annulated quinoline rings (Equation 21 <1999H(51)2861>). 

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