Pyridine-2-thione, 3-amino

Several 2,3-dihydrooxazolo pyridine-2-thiones have been prepared by reacting pyridines, having amino and hydroxy groups in ortho position to one another, with carbon disulfide in alcoholic potassium hydroxide. A hsting of these substances is given in Table 13. 

The reaction of 6-amino[l,2,4]triazin-5(2//)-ones or its thione derivatives 680 with acetic anhydride gave the 6-acetamido derivatives 681 and 682, respectively. Treatment with phosphorus pentasulfide in pyridine gave thiazolo[5,4-e][l,2,4]triazines 683 (84LA283 87AJC491) (Scheme 142). 

Similar studies have recently been extended to aminopyridones and thiones and to aminopyrimidones (Barlin jmd Pfleiderer, 1971 Barlin, 1972). Protonation of 3- and 5-amino-2-hydroxypyridine and 3,4-diamino-2-hydroxypyridine occurs first at the 3- (or 5-) amino-group, but 4- and 6-amino-2-hydroxypyridine and 2- and 3-amino-4-hydroxypyridine first protonate at the oxygen atom, because the amino-group is involved in conjugation with the partially positively charged ring nitrogen. Similar results are found for the amino-pyridine-2(and 4)-thiones (Barlin, 1972). 

Reaction of 4-arylidene-2-phenyl-5(4//)-oxazolones 593 with A-phenacylpyri-dinium bromide proceeds by the same sequence to give oxazolo[5,4-/>]pyridines 594 (Scheme 7.188) while the reaction of 4-(aminomethylene)-2-phenyl-5(4//)-oxazolone 418 and phenyl isothiocyanate gives pyrimidin-2-thiones 595 (Scheme 7.189). In this latter case initial attack of the exocylic amino group produces an intermediate thiourea (not shown) that subsequently cyclizes to 595. 

Brassilexin 48 and sinalexin 49 are among the most potent phytoalexins produced by economically important cruciferous plants. The most efficient preparation of brassilexin 48, sinalexin 49, and analogues 52 reported uses a Vilsmeier formylation-amination of readily available indoline-2-thiones 50 followed by an aqueous ammonia work-up procedure with subsequent oxidation of the 3-(amino)methyleneindoline-2-thione intermediates 51 using iodine in pyridine (Scheme 10) <20010L1213, 2005JOC1828>. The reaction yields are dictated by the efficiency of the... 

A Thorpe-Ziegler intramolecular cyclization starting with 3-cyanopyridine-2-thione derivatives leads to the formation of 3-amino-2-(organylsulfinyl)thieno[2,3- ]pyridines in high yields <2006RCB529>. 

A similar series of nucleophilic substitutions has been performed on 4-chloro[l,2,3]triazolo[4,5-c]pyridine (246) and some of its simple substituted derivatives. On compound 246 itself formic acid gives the triazolo-pyridin-4-one,192 ammonia gives the 4-amino compound,192 and hydrazine the 4-hydrazino derivative 245 hydrosulfide gives the 4-thione192 and thiourea in propanol, at first reported151 to give the 4-thione, has subsequently been... 

Reactions of 5f/-2-methyl-l,2,4-triazepino[2,3- ]benzimidazol-4-one 71, prepared by reaction of 1,2-diaminobenz-imidazole 72 with acetoacetic ester 73, with different reagents was described, in the search of new heterocycles with biological activity <2002CHE598>. When lactam 71 was treated with aromatic aldehydes in boiling 1-BuOH with addition of piperidine 74, 577-3-arylidene-2-methyl-l,2,4-triazepino[2,3- ]benzimidazol-4-ones 75a-c were obtained (Scheme 7). Coupling lactam 71 with phenyldiazonium chloride 76 in dioxane afforded the 3-phenylazo-substituted tricycle 77. When 71 was treated with phosphorus pentasulfide 78 in boiling dioxane or pyridine, its thio analog 79 was obtained. The reaction proceeded most efficiently when lactam 71 was refluxed with twofold excess of 78 in dry dioxane. These thiones 79 react with ammonia and amines by nucleophilic substitution. When 79 was refluxed with ammonia, benzylamine, piperidine, or morpholine, the 4-amino-substituted tricycles 80a-d were obtained. All the described compounds were identified by NMR, mass spectrometry, and IR spectroscopy. 

Publications on other types of rearrangements involving tetrazoles are cited at length in a review <2004SOS(13)861> in particular, the Smiles rearrangement of 2-[(l-alkyl/aryl-17/-tetrazol-5-yl)sulfanyl]pyridine-3-amines 208 to 3-[(l-alkyl/aryl-l/7-tetrazol-5-yl)amino]pyridine-2(l/f)-thiones 209 under acidic conditions and Smiles rearrangement of 5-sulfanyl/sulfone-substituted tetrazoles 210 to tetrazol-5-amines 211 under basic conditions (Scheme 19) <2004SOS(13)861>. 

The tautomerism between 2-pyridinethione and 2-pyridine thiol has also been examined using variable temperature IR spectroscopy <2002JOC9061>. No evidence for the S-H stretch was observed in a range of solvents and this was determined computationally to be a solvent effect the thiol form is more stable in the gas phase but the thione is more stable in solution. (The effect of phase on the tautomers of 2-hydroxy, 2-amino-, and 2-thiopyridine has also been studied by infrared spectroscopy <2001SAA2659>.) Dimerization is also observed, with the indication that the thione dimer predominates, in contrast with the computational studies described above. 

Diazotization of 3-amino-2-thiolpyridine (556) gave thiadiazolo[5,4-fi]pyridine (557) which on treatment with carbon disulfide at 220 °C furnished 1,3-dithiolo[4,5-fi]pyridine-2-thione (558) (46%) (Scheme 71) <78PJC2039>. 

Similarly, treatment of 5-amino-7-chloro-l//-[l,2,3]triazolo[4,5-6]pyridine (254) with sodium hydrosulfide-butanol affords 5-amino-l,4-dihydro-7//-[l,2,3]triazolo[4,5-6]pyridine-7-thione (1-deaza-8-aza-6-thioguanine) (255b) which isomerizes to 4,6-diamino[l,2,3]thiadiazole[4,5-c]pyridine (257b) in A,A-dimethylacetamide (125°C) <76JOC3784>. 

A reversible Dimroth rearrangement is observed between 1,4-dihydro-7if-w-triazolo[4,5-f>]pyridine-7-thione (655) and 4-amino[l,2,3]thiadiazolo[4,5-c]pyridine (657) on heating... 

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